llvm/docs/AMDGPUUsage.rst

=============================
User Guide for AMDGPU Backend
=============================

.. contents::
   :local:

Introduction
============

The AMDGPU backend provides ISA code generation for AMD GPUs, starting with the
R600 family up until the current GCN families. It lives in the
``lib/Target/AMDGPU`` directory.

LLVM
====

.. _amdgpu-target-triples:

Target Triples
--------------

Use the ``clang -target <Architecture>-<Vendor>-<OS>-<Environment>`` option to
specify the target triple:

  .. table:: AMDGPU Architectures
     :name: amdgpu-architecture-table

     ============ ==============================================================
     Architecture Description
     ============ ==============================================================
     ``r600``     AMD GPUs HD2XXX-HD6XXX for graphics and compute shaders.
     ``amdgcn``   AMD GPUs GCN GFX6 onwards for graphics and compute shaders.
     ============ ==============================================================

  .. table:: AMDGPU Vendors
     :name: amdgpu-vendor-table

     ============ ==============================================================
     Vendor       Description
     ============ ==============================================================
     ``amd``      Can be used for all AMD GPU usage.
     ``mesa3d``   Can be used if the OS is ``mesa3d``.
     ============ ==============================================================

  .. table:: AMDGPU Operating Systems
     :name: amdgpu-os-table

     ============== ============================================================
     OS             Description
     ============== ============================================================
     *<empty>*      Defaults to the *unknown* OS.
     ``amdhsa``     Compute kernels executed on HSA [HSA]_ compatible runtimes
                    such as AMD's ROCm [AMD-ROCm]_.
     ``amdpal``     Graphic shaders and compute kernels executed on AMD PAL
                    runtime.
     ``mesa3d``     Graphic shaders and compute kernels executed on Mesa 3D
                    runtime.
     ============== ============================================================

  .. table:: AMDGPU Environments
     :name: amdgpu-environment-table

     ============ ==============================================================
     Environment  Description
     ============ ==============================================================
     *<empty>*    Defaults to ``opencl``.
     ``opencl``   OpenCL compute kernel (see :ref:`amdgpu-opencl`).
     ``amdgizcl`` Same as ``opencl`` except a different address space mapping is
                  used (see :ref:`amdgpu-address-spaces`).
     ``amdgiz``   Same as ``opencl`` except a different address space mapping is
                  used (see :ref:`amdgpu-address-spaces`).
     ``hcc``      AMD HC language compute kernel (see :ref:`amdgpu-hcc`).
     ============ ==============================================================

.. _amdgpu-processors:

Processors
----------

Use the ``clang -mcpu <Processor>`` option to specify the AMD GPU processor. The
names from both the *Processor* and *Alternative Processor* can be used.

  .. table:: AMDGPU Processors
     :name: amdgpu-processor-table

     =========== =============== ============ ===== ========= ======= ==================
     Processor   Alternative     Target       dGPU/ Target    ROCm    Example
                 Processor       Triple       APU   Features  Support Products
                                 Architecture       Supported
                                                    [Default]
     =========== =============== ============ ===== ========= ======= ==================
     **Radeon HD 2000/3000 Series (R600)** [AMD-RADEON-HD-2000-3000]_
     -----------------------------------------------------------------------------------
     ``r600``                    ``r600``     dGPU
     ``r630``                    ``r600``     dGPU
     ``rs880``                   ``r600``     dGPU
     ``rv670``                   ``r600``     dGPU
     **Radeon HD 4000 Series (R700)** [AMD-RADEON-HD-4000]_
     -----------------------------------------------------------------------------------
     ``rv710``                   ``r600``     dGPU
     ``rv730``                   ``r600``     dGPU
     ``rv770``                   ``r600``     dGPU
     **Radeon HD 5000 Series (Evergreen)** [AMD-RADEON-HD-5000]_
     -----------------------------------------------------------------------------------
     ``cedar``                   ``r600``     dGPU
     ``redwood``                 ``r600``     dGPU
     ``sumo``                    ``r600``     dGPU
     ``juniper``                 ``r600``     dGPU
     ``cypress``                 ``r600``     dGPU
     **Radeon HD 6000 Series (Northern Islands)** [AMD-RADEON-HD-6000]_
     -----------------------------------------------------------------------------------
     ``barts``                   ``r600``     dGPU
     ``turks``                   ``r600``     dGPU
     ``caicos``                  ``r600``     dGPU
     ``cayman``                  ``r600``     dGPU
     **GCN GFX6 (Southern Islands (SI))** [AMD-GCN-GFX6]_
     -----------------------------------------------------------------------------------
     ``gfx600``  - ``tahiti``    ``amdgcn``   dGPU
     ``gfx601``  - ``pitcairn``  ``amdgcn``   dGPU
                 - ``verde``
                 - ``oland``
                 - ``hainan``
     **GCN GFX7 (Sea Islands (CI))** [AMD-GCN-GFX7]_
     -----------------------------------------------------------------------------------
     ``gfx700``  - ``kaveri``    ``amdgcn``   APU                     - A6-7000
                                                                      - A6 Pro-7050B
                                                                      - A8-7100
                                                                      - A8 Pro-7150B
                                                                      - A10-7300
                                                                      - A10 Pro-7350B
                                                                      - FX-7500
                                                                      - A8-7200P
                                                                      - A10-7400P
                                                                      - FX-7600P
     ``gfx701``  - ``hawaii``    ``amdgcn``   dGPU            ROCm    - FirePro W8100
                                                                      - FirePro W9100
                                                                      - FirePro S9150
                                                                      - FirePro S9170
     ``gfx702``                  ``amdgcn``   dGPU            ROCm    - Radeon R9 290
                                                                      - Radeon R9 290x
                                                                      - Radeon R390
                                                                      - Radeon R390x
     ``gfx703``  - ``kabini``    ``amdgcn``   APU                     - E1-2100
                 - ``mullins``                                        - E1-2200
                                                                      - E1-2500
                                                                      - E2-3000
                                                                      - E2-3800
                                                                      - A4-5000
                                                                      - A4-5100
                                                                      - A6-5200
                                                                      - A4 Pro-3340B
     ``gfx704``  - ``bonaire``   ``amdgcn``   dGPU                    - Radeon HD 7790
                                                                      - Radeon HD 8770
                                                                      - R7 260
                                                                      - R7 260X
     **GCN GFX8 (Volcanic Islands (VI))** [AMD-GCN-GFX8]_
     -----------------------------------------------------------------------------------
     ``gfx801``  - ``carrizo``   ``amdgcn``   APU   - xnack           - A6-8500P
                                                      [on]            - Pro A6-8500B
                                                                      - A8-8600P
                                                                      - Pro A8-8600B
                                                                      - FX-8800P
                                                                      - Pro A12-8800B
     \                           ``amdgcn``   APU   - xnack   ROCm    - A10-8700P
                                                      [on]            - Pro A10-8700B
                                                                      - A10-8780P
     \                           ``amdgcn``   APU   - xnack           - A10-9600P
                                                      [on]            - A10-9630P
                                                                      - A12-9700P
                                                                      - A12-9730P
                                                                      - FX-9800P
                                                                      - FX-9830P
     \                           ``amdgcn``   APU   - xnack           - E2-9010
                                                      [on]            - A6-9210
                                                                      - A9-9410
     ``gfx802``  - ``tonga``     ``amdgcn``   dGPU  - xnack   ROCm    - FirePro S7150
                 - ``iceland``                        [off]           - FirePro S7100
                                                                      - FirePro W7100
                                                                      - Radeon R285
                                                                      - Radeon R9 380
                                                                      - Radeon R9 385
                                                                      - Mobile FirePro
                                                                        M7170
     ``gfx803``  - ``fiji``      ``amdgcn``   dGPU  - xnack   ROCm    - Radeon R9 Nano
                                                      [off]           - Radeon R9 Fury
                                                                      - Radeon R9 FuryX
                                                                      - Radeon Pro Duo
                                                                      - FirePro S9300x2
                                                                      - Radeon Instinct MI8
     \           - ``polaris10`` ``amdgcn``   dGPU  - xnack   ROCm    - Radeon RX 470
                                                      [off]           - Radeon RX 480
                                                                      - Radeon Instinct MI6
     \           - ``polaris11`` ``amdgcn``   dGPU  - xnack   ROCm    - Radeon RX 460
                                                      [off]
     ``gfx810``  - ``stoney``    ``amdgcn``   APU   - xnack
                                                      [on]
     **GCN GFX9** [AMD-GCN-GFX9]_
     -----------------------------------------------------------------------------------
     ``gfx900``                  ``amdgcn``   dGPU  - xnack   ROCm    - Radeon Vega
                                                      [off]             Frontier Edition
                                                                      - Radeon RX Vega 56
                                                                      - Radeon RX Vega 64
                                                                      - Radeon RX Vega 64
                                                                        Liquid
                                                                      - Radeon Instinct MI25
     ``gfx902``                  ``amdgcn``   APU   - xnack           *TBA*
                                                      [on]
                                                                      .. TODO
                                                                         Add product
                                                                         names.
     =========== =============== ============ ===== ========= ======= ==================

.. _amdgpu-target-features:

Target Features
---------------

Target features control how code is generated to support certain
processor specific features. Not all target features are supported by
all processors. The runtime must ensure that the features supported by
the device used to execute the code match the features enabled when
generating the code. A mismatch of features may result in incorrect
execution, or a reduction in performance.

The target features supported by each processor, and the default value
used if not specified explicitly, is listed in
:ref:`amdgpu-processor-table`.

Use the ``clang -m[no-]<TargetFeature>`` option to specify the AMD GPU
target features.

For example:

``-mxnack``
  Enable the ``xnack`` feature.
``-mno-xnack``
  Disable the ``xnack`` feature.

  .. table:: AMDGPU Target Features
     :name: amdgpu-target-feature-table

     ============== ==================================================
     Target Feature Description
     ============== ==================================================
     -m[no-]xnack   Enable/disable generating code that has
                    memory clauses that are compatible with
                    having XNACK replay enabled.

                    This is used for demand paging and page
                    migration. If XNACK replay is enabled in
                    the device, then if a page fault occurs
                    the code may execute incorrectly if the
                    ``xnack`` feature is not enabled. Executing
                    code that has the feature enabled on a
                    device that does not have XNACK replay
                    enabled will execute correctly, but may
                    be less performant than code with the
                    feature disabled.
     ============== ==================================================

.. _amdgpu-address-spaces:

Address Spaces
--------------

The AMDGPU backend uses the following address space mappings.

The memory space names used in the table, aside from the region memory space, is
from the OpenCL standard.

LLVM Address Space number is used throughout LLVM (for example, in LLVM IR).

  .. table:: Address Space Mapping
     :name: amdgpu-address-space-mapping-table

     ================== ================= ================= ================= =================
     LLVM Address Space Memory Space
     ------------------ -----------------------------------------------------------------------
     \                  Current Default   amdgiz/amdgizcl   hcc               Future Default
     ================== ================= ================= ================= =================
     0                  Private (Scratch) Generic (Flat)    Generic (Flat)    Generic (Flat)
     1                  Global            Global            Global            Global
     2                  Constant          Constant          Constant          Region (GDS)
     3                  Local (group/LDS) Local (group/LDS) Local (group/LDS) Local (group/LDS)
     4                  Generic (Flat)    Region (GDS)      Region (GDS)      Constant
     5                  Region (GDS)      Private (Scratch) Private (Scratch) Private (Scratch)
     ================== ================= ================= ================= =================

Current Default
  This is the current default address space mapping used for all languages
  except hcc. This will shortly be deprecated.

amdgiz/amdgizcl
  This is the current address space mapping used when ``amdgiz`` or ``amdgizcl``
  is specified as the target triple environment value.

hcc
  This is the current address space mapping used when ``hcc`` is specified as
  the target triple environment value.This will shortly be deprecated.

Future Default
  This will shortly be the only address space mapping for all languages using
  AMDGPU backend.

.. _amdgpu-memory-scopes:

Memory Scopes
-------------

This section provides LLVM memory synchronization scopes supported by the AMDGPU
backend memory model when the target triple OS is ``amdhsa`` (see
:ref:`amdgpu-amdhsa-memory-model` and :ref:`amdgpu-target-triples`).

The memory model supported is based on the HSA memory model [HSA]_ which is
based in turn on HRF-indirect with scope inclusion [HRF]_. The happens-before
relation is transitive over the synchonizes-with relation independent of scope,
and synchonizes-with allows the memory scope instances to be inclusive (see
table :ref:`amdgpu-amdhsa-llvm-sync-scopes-table`).

This is different to the OpenCL [OpenCL]_ memory model which does not have scope
inclusion and requires the memory scopes to exactly match. However, this
is conservatively correct for OpenCL.

  .. table:: AMDHSA LLVM Sync Scopes
     :name: amdgpu-amdhsa-llvm-sync-scopes-table

     ================ ==========================================================
     LLVM Sync Scope  Description
     ================ ==========================================================
     *none*           The default: ``system``.

                      Synchronizes with, and participates in modification and
                      seq_cst total orderings with, other operations (except
                      image operations) for all address spaces (except private,
                      or generic that accesses private) provided the other
                      operation's sync scope is:

                      - ``system``.
                      - ``agent`` and executed by a thread on the same agent.
                      - ``workgroup`` and executed by a thread in the same
                        workgroup.
                      - ``wavefront`` and executed by a thread in the same
                        wavefront.

     ``agent``        Synchronizes with, and participates in modification and
                      seq_cst total orderings with, other operations (except
                      image operations) for all address spaces (except private,
                      or generic that accesses private) provided the other
                      operation's sync scope is:

                      - ``system`` or ``agent`` and executed by a thread on the
                        same agent.
                      - ``workgroup`` and executed by a thread in the same
                        workgroup.
                      - ``wavefront`` and executed by a thread in the same
                        wavefront.

     ``workgroup``    Synchronizes with, and participates in modification and
                      seq_cst total orderings with, other operations (except
                      image operations) for all address spaces (except private,
                      or generic that accesses private) provided the other
                      operation's sync scope is:

                      - ``system``, ``agent`` or ``workgroup`` and executed by a
                        thread in the same workgroup.
                      - ``wavefront`` and executed by a thread in the same
                        wavefront.

     ``wavefront``    Synchronizes with, and participates in modification and
                      seq_cst total orderings with, other operations (except
                      image operations) for all address spaces (except private,
                      or generic that accesses private) provided the other
                      operation's sync scope is:

                      - ``system``, ``agent``, ``workgroup`` or ``wavefront``
                        and executed by a thread in the same wavefront.

     ``singlethread`` Only synchronizes with, and participates in modification
                      and seq_cst total orderings with, other operations (except
                      image operations) running in the same thread for all
                      address spaces (for example, in signal handlers).
     ================ ==========================================================

AMDGPU Intrinsics
-----------------

The AMDGPU backend implements the following intrinsics.

*This section is WIP.*

.. TODO
   List AMDGPU intrinsics

Code Object
===========

The AMDGPU backend generates a standard ELF [ELF]_ relocatable code object that
can be linked by ``lld`` to produce a standard ELF shared code object which can
be loaded and executed on an AMDGPU target.

Header
------

The AMDGPU backend uses the following ELF header:

  .. table:: AMDGPU ELF Header
     :name: amdgpu-elf-header-table

     ========================== ===============================
     Field                      Value
     ========================== ===============================
     ``e_ident[EI_CLASS]``      ``ELFCLASS64``
     ``e_ident[EI_DATA]``       ``ELFDATA2LSB``
     ``e_ident[EI_OSABI]``      - ``ELFOSABI_NONE``
                                - ``ELFOSABI_AMDGPU_HSA``
                                - ``ELFOSABI_AMDGPU_PAL``
                                - ``ELFOSABI_AMDGPU_MESA3D``
     ``e_ident[EI_ABIVERSION]`` - ``ELFABIVERSION_AMDGPU_HSA``
                                - ``ELFABIVERSION_AMDGPU_PAL``
                                - ``ELFABIVERSION_AMDGPU_MESA3D``
     ``e_type``                 - ``ET_REL``
                                - ``ET_DYN``
     ``e_machine``              ``EM_AMDGPU``
     ``e_entry``                0
     ``e_flags``                See :ref:`amdgpu-elf-header-e_flags-table`
     ========================== ===============================

..

  .. table:: AMDGPU ELF Header Enumeration Values
     :name: amdgpu-elf-header-enumeration-values-table

     =============================== =====
     Name                            Value
     =============================== =====
     ``EM_AMDGPU``                   224
     ``ELFOSABI_NONE``               0
     ``ELFOSABI_AMDGPU_HSA``         64
     ``ELFOSABI_AMDGPU_PAL``         65
     ``ELFOSABI_AMDGPU_MESA3D``      66
     ``ELFABIVERSION_AMDGPU_HSA``    1
     ``ELFABIVERSION_AMDGPU_PAL``    0
     ``ELFABIVERSION_AMDGPU_MESA3D`` 0
     =============================== =====

``e_ident[EI_CLASS]``
  The ELF class is:

  * ``ELFCLASS32`` for ``r600`` architecture.

  * ``ELFCLASS64`` for ``amdgcn`` architecture which only supports 64
    bit applications.

``e_ident[EI_DATA]``
  All AMDGPU targets use ``ELFDATA2LSB`` for little-endian byte ordering.

``e_ident[EI_OSABI]``
  One of the following AMD GPU architecture specific OS ABIs
  (see :ref:`amdgpu-os-table`):

  * ``ELFOSABI_NONE`` for *unknown* OS.

  * ``ELFOSABI_AMDGPU_HSA`` for ``amdhsa`` OS.

  * ``ELFOSABI_AMDGPU_PAL`` for ``amdpal`` OS.

  * ``ELFOSABI_AMDGPU_MESA3D`` for ``mesa3D`` OS.

``e_ident[EI_ABIVERSION]``
  The ABI version of the AMD GPU architecture specific OS ABI to which the code
  object conforms:

  * ``ELFABIVERSION_AMDGPU_HSA`` is used to specify the version of AMD HSA
    runtime ABI.

  * ``ELFABIVERSION_AMDGPU_PAL`` is used to specify the version of AMD PAL
    runtime ABI.

  * ``ELFABIVERSION_AMDGPU_MESA3D`` is used to specify the version of AMD MESA
    3D runtime ABI.

``e_type``
  Can be one of the following values:


  ``ET_REL``
    The type produced by the AMD GPU backend compiler as it is relocatable code
    object.

  ``ET_DYN``
    The type produced by the linker as it is a shared code object.

  The AMD HSA runtime loader requires a ``ET_DYN`` code object.

``e_machine``
  The value ``EM_AMDGPU`` is used for the machine for all processors supported
  by the ``r600`` and ``amdgcn`` architectures (see
  :ref:`amdgpu-processor-table`). The specific processor is specified in the
  ``EF_AMDGPU_MACH`` bit field of the ``e_flags`` (see
  :ref:`amdgpu-elf-header-e_flags-table`).

``e_entry``
  The entry point is 0 as the entry points for individual kernels must be
  selected in order to invoke them through AQL packets.

``e_flags``
  The AMDGPU backend uses the following ELF header flags:

  .. table:: AMDGPU ELF Header ``e_flags``
     :name: amdgpu-elf-header-e_flags-table

     ================================= ========== =============================
     Name                              Value      Description
     ================================= ========== =============================
     **AMDGPU Processor Flag**                    See :ref:`amdgpu-processor-table`.
     -------------------------------------------- -----------------------------
     ``EF_AMDGPU_MACH``                0x000000ff AMDGPU processor selection
                                                  mask for
                                                  ``EF_AMDGPU_MACH_xxx`` values
                                                  defined in
                                                  :ref:`amdgpu-ef-amdgpu-mach-table`.
     ``EF_AMDGPU_XNACK``               0x00000100 Indicates if the ``xnack``
                                                  target feature is
                                                  enabled for all code
                                                  contained in the code object.
                                                  See
                                                  :ref:`amdgpu-target-features`.
     ================================= ========== =============================

  .. table:: AMDGPU ``EF_AMDGPU_MACH`` Values
     :name: amdgpu-ef-amdgpu-mach-table

     ================================= ========== =============================
     Name                              Value      Description (see
                                                  :ref:`amdgpu-processor-table`)
     ================================= ========== =============================
     ``EF_AMDGPU_MACH_NONE``           0          *not specified*
     ``EF_AMDGPU_MACH_R600_R600``      1          ``r600``
     ``EF_AMDGPU_MACH_R600_R630``      2          ``r630``
     ``EF_AMDGPU_MACH_R600_RS880``     3          ``rs880``
     ``EF_AMDGPU_MACH_R600_RV670``     4          ``rv670``
     ``EF_AMDGPU_MACH_R600_RV710``     5          ``rv710``
     ``EF_AMDGPU_MACH_R600_RV730``     6          ``rv730``
     ``EF_AMDGPU_MACH_R600_RV770``     7          ``rv770``
     ``EF_AMDGPU_MACH_R600_CEDAR``     8          ``cedar``
     ``EF_AMDGPU_MACH_R600_REDWOOD``   9          ``redwood``
     ``EF_AMDGPU_MACH_R600_SUMO``      10         ``sumo``
     ``EF_AMDGPU_MACH_R600_JUNIPER``   11         ``juniper``
     ``EF_AMDGPU_MACH_R600_CYPRESS``   12         ``cypress``
     ``EF_AMDGPU_MACH_R600_BARTS``     13         ``barts``
     ``EF_AMDGPU_MACH_R600_TURKS``     14         ``turks``
     ``EF_AMDGPU_MACH_R600_CAICOS``    15         ``caicos``
     ``EF_AMDGPU_MACH_R600_CAYMAN``    16         ``cayman``
     *reserved*                        17-31      Reserved for ``r600``
                                                  architecture processors.
     ``EF_AMDGPU_MACH_AMDGCN_GFX600``  32         ``gfx600``
     ``EF_AMDGPU_MACH_AMDGCN_GFX601``  33         ``gfx601``
     ``EF_AMDGPU_MACH_AMDGCN_GFX700``  34         ``gfx700``
     ``EF_AMDGPU_MACH_AMDGCN_GFX701``  35         ``gfx701``
     ``EF_AMDGPU_MACH_AMDGCN_GFX702``  36         ``gfx702``
     ``EF_AMDGPU_MACH_AMDGCN_GFX703``  37         ``gfx703``
     ``EF_AMDGPU_MACH_AMDGCN_GFX704``  38         ``gfx704``
     *reserved*                        39         Reserved.
     ``EF_AMDGPU_MACH_AMDGCN_GFX801``  40         ``gfx801``
     ``EF_AMDGPU_MACH_AMDGCN_GFX802``  41         ``gfx802``
     ``EF_AMDGPU_MACH_AMDGCN_GFX803``  42         ``gfx803``
     ``EF_AMDGPU_MACH_AMDGCN_GFX810``  43         ``gfx810``
     ``EF_AMDGPU_MACH_AMDGCN_GFX900``  44         ``gfx900``
     ``EF_AMDGPU_MACH_AMDGCN_GFX902``  45         ``gfx902``
     ================================= ========== =============================

Sections
--------

An AMDGPU target ELF code object has the standard ELF sections which include:

  .. table:: AMDGPU ELF Sections
     :name: amdgpu-elf-sections-table

     ================== ================ =================================
     Name               Type             Attributes
     ================== ================ =================================
     ``.bss``           ``SHT_NOBITS``   ``SHF_ALLOC`` + ``SHF_WRITE``
     ``.data``          ``SHT_PROGBITS`` ``SHF_ALLOC`` + ``SHF_WRITE``
     ``.debug_``\ *\**  ``SHT_PROGBITS`` *none*
     ``.dynamic``       ``SHT_DYNAMIC``  ``SHF_ALLOC``
     ``.dynstr``        ``SHT_PROGBITS`` ``SHF_ALLOC``
     ``.dynsym``        ``SHT_PROGBITS`` ``SHF_ALLOC``
     ``.got``           ``SHT_PROGBITS`` ``SHF_ALLOC`` + ``SHF_WRITE``
     ``.hash``          ``SHT_HASH``     ``SHF_ALLOC``
     ``.note``          ``SHT_NOTE``     *none*
     ``.rela``\ *name*  ``SHT_RELA``     *none*
     ``.rela.dyn``      ``SHT_RELA``     *none*
     ``.rodata``        ``SHT_PROGBITS`` ``SHF_ALLOC``
     ``.shstrtab``      ``SHT_STRTAB``   *none*
     ``.strtab``        ``SHT_STRTAB``   *none*
     ``.symtab``        ``SHT_SYMTAB``   *none*
     ``.text``          ``SHT_PROGBITS`` ``SHF_ALLOC`` + ``SHF_EXECINSTR``
     ================== ================ =================================

These sections have their standard meanings (see [ELF]_) and are only generated
if needed.

``.debug``\ *\**
  The standard DWARF sections. See :ref:`amdgpu-dwarf` for information on the
  DWARF produced by the AMDGPU backend.

``.dynamic``, ``.dynstr``, ``.dynsym``, ``.hash``
  The standard sections used by a dynamic loader.

``.note``
  See :ref:`amdgpu-note-records` for the note records supported by the AMDGPU
  backend.

``.rela``\ *name*, ``.rela.dyn``
  For relocatable code objects, *name* is the name of the section that the
  relocation records apply. For example, ``.rela.text`` is the section name for
  relocation records associated with the ``.text`` section.

  For linked shared code objects, ``.rela.dyn`` contains all the relocation
  records from each of the relocatable code object's ``.rela``\ *name* sections.

  See :ref:`amdgpu-relocation-records` for the relocation records supported by
  the AMDGPU backend.

``.text``
  The executable machine code for the kernels and functions they call. Generated
  as position independent code. See :ref:`amdgpu-code-conventions` for
  information on conventions used in the isa generation.

.. _amdgpu-note-records:

Note Records
------------

As required by ``ELFCLASS32`` and ``ELFCLASS64``, minimal zero byte padding must
be generated after the ``name`` field to ensure the ``desc`` field is 4 byte
aligned. In addition, minimal zero byte padding must be generated to ensure the
``desc`` field size is a multiple of 4 bytes. The ``sh_addralign`` field of the
``.note`` section must be at least 4 to indicate at least 8 byte alignment.

The AMDGPU backend code object uses the following ELF note records in the
``.note`` section. The *Description* column specifies the layout of the note
record's ``desc`` field. All fields are consecutive bytes. Note records with
variable size strings have a corresponding ``*_size`` field that specifies the
number of bytes, including the terminating null character, in the string. The
string(s) come immediately after the preceding fields.

Additional note records can be present.

  .. table:: AMDGPU ELF Note Records
     :name: amdgpu-elf-note-records-table

     ===== ============================== ======================================
     Name  Type                           Description
     ===== ============================== ======================================
     "AMD" ``NT_AMD_AMDGPU_HSA_METADATA`` <metadata null terminated string>
     ===== ============================== ======================================

..

  .. table:: AMDGPU ELF Note Record Enumeration Values
     :name: amdgpu-elf-note-record-enumeration-values-table

     ============================== =====
     Name                           Value
     ============================== =====
     *reserved*                       0-9
     ``NT_AMD_AMDGPU_HSA_METADATA``    10
     *reserved*                        11
     ============================== =====

``NT_AMD_AMDGPU_HSA_METADATA``
  Specifies extensible metadata associated with the code objects executed on HSA
  [HSA]_ compatible runtimes such as AMD's ROCm [AMD-ROCm]_. It is required when
  the target triple OS is ``amdhsa`` (see :ref:`amdgpu-target-triples`). See
  :ref:`amdgpu-amdhsa-hsa-code-object-metadata` for the syntax of the code
  object metadata string.

.. _amdgpu-symbols:

Symbols
-------

Symbols include the following:

  .. table:: AMDGPU ELF Symbols
     :name: amdgpu-elf-symbols-table

     ===================== ============== ============= ==================
     Name                  Type           Section       Description
     ===================== ============== ============= ==================
     *link-name*           ``STT_OBJECT`` - ``.data``   Global variable
                                          - ``.rodata``
                                          - ``.bss``
     *link-name*\ ``@kd``  ``STT_OBJECT`` - ``.rodata`` Kernel descriptor
     *link-name*           ``STT_FUNC``   - ``.text``   Kernel entry point
     ===================== ============== ============= ==================

Global variable
  Global variables both used and defined by the compilation unit.

  If the symbol is defined in the compilation unit then it is allocated in the
  appropriate section according to if it has initialized data or is readonly.

  If the symbol is external then its section is ``STN_UNDEF`` and the loader
  will resolve relocations using the definition provided by another code object
  or explicitly defined by the runtime.

  All global symbols, whether defined in the compilation unit or external, are
  accessed by the machine code indirectly through a GOT table entry. This
  allows them to be preemptable. The GOT table is only supported when the target
  triple OS is ``amdhsa`` (see :ref:`amdgpu-target-triples`).

  .. TODO
     Add description of linked shared object symbols. Seems undefined symbols
     are marked as STT_NOTYPE.

Kernel descriptor
  Every HSA kernel has an associated kernel descriptor. It is the address of the
  kernel descriptor that is used in the AQL dispatch packet used to invoke the
  kernel, not the kernel entry point. The layout of the HSA kernel descriptor is
  defined in :ref:`amdgpu-amdhsa-kernel-descriptor`.

Kernel entry point
  Every HSA kernel also has a symbol for its machine code entry point.

.. _amdgpu-relocation-records:

Relocation Records
------------------

AMDGPU backend generates ``Elf64_Rela`` relocation records. Supported
relocatable fields are:

``word32``
  This specifies a 32-bit field occupying 4 bytes with arbitrary byte
  alignment. These values use the same byte order as other word values in the
  AMD GPU architecture.

``word64``
  This specifies a 64-bit field occupying 8 bytes with arbitrary byte
  alignment. These values use the same byte order as other word values in the
  AMD GPU architecture.

Following notations are used for specifying relocation calculations:

**A**
  Represents the addend used to compute the value of the relocatable field.

**G**
  Represents the offset into the global offset table at which the relocation
  entry's symbol will reside during execution.

**GOT**
  Represents the address of the global offset table.

**P**
  Represents the place (section offset for ``et_rel`` or address for ``et_dyn``)
  of the storage unit being relocated (computed using ``r_offset``).

**S**
  Represents the value of the symbol whose index resides in the relocation
  entry. Relocations not using this must specify a symbol index of ``STN_UNDEF``.

**B**
  Represents the base address of a loaded executable or shared object which is
  the difference between the ELF address and the actual load address. Relocations
  using this are only valid in executable or shared objects.

The following relocation types are supported:

  .. table:: AMDGPU ELF Relocation Records
     :name: amdgpu-elf-relocation-records-table

     ========================== ======= =====  ==========  ==============================
     Relocation Type            Kind    Value  Field       Calculation
     ========================== ======= =====  ==========  ==============================
     ``R_AMDGPU_NONE``                  0      *none*      *none*
     ``R_AMDGPU_ABS32_LO``      Dynamic 1      ``word32``  (S + A) & 0xFFFFFFFF
     ``R_AMDGPU_ABS32_HI``      Dynamic 2      ``word32``  (S + A) >> 32
     ``R_AMDGPU_ABS64``         Dynamic 3      ``word64``  S + A
     ``R_AMDGPU_REL32``         Static  4      ``word32``  S + A - P
     ``R_AMDGPU_REL64``         Static  5      ``word64``  S + A - P
     ``R_AMDGPU_ABS32``         Static  6      ``word32``  S + A
     ``R_AMDGPU_GOTPCREL``      Static  7      ``word32``  G + GOT + A - P
     ``R_AMDGPU_GOTPCREL32_LO`` Static  8      ``word32``  (G + GOT + A - P) & 0xFFFFFFFF
     ``R_AMDGPU_GOTPCREL32_HI`` Static  9      ``word32``  (G + GOT + A - P) >> 32
     ``R_AMDGPU_REL32_LO``      Static  10     ``word32``  (S + A - P) & 0xFFFFFFFF
     ``R_AMDGPU_REL32_HI``      Static  11     ``word32``  (S + A - P) >> 32
     *reserved*                         12
     ``R_AMDGPU_RELATIVE64``    Dynamic 13     ``word64``  B + A
     ========================== ======= =====  ==========  ==============================

.. _amdgpu-dwarf:

DWARF
-----

Standard DWARF [DWARF]_ Version 2 sections can be generated. These contain
information that maps the code object executable code and data to the source
language constructs. It can be used by tools such as debuggers and profilers.

Address Space Mapping
~~~~~~~~~~~~~~~~~~~~~

The following address space mapping is used:

  .. table:: AMDGPU DWARF Address Space Mapping
     :name: amdgpu-dwarf-address-space-mapping-table

     =================== =================
     DWARF Address Space Memory Space
     =================== =================
     1                   Private (Scratch)
     2                   Local (group/LDS)
     *omitted*           Global
     *omitted*           Constant
     *omitted*           Generic (Flat)
     *not supported*     Region (GDS)
     =================== =================

See :ref:`amdgpu-address-spaces` for information on the memory space terminology
used in the table.

An ``address_class`` attribute is generated on pointer type DIEs to specify the
DWARF address space of the value of the pointer when it is in the *private* or
*local* address space. Otherwise the attribute is omitted.

An ``XDEREF`` operation is generated in location list expressions for variables
that are allocated in the *private* and *local* address space. Otherwise no
``XDREF`` is omitted.

Register Mapping
~~~~~~~~~~~~~~~~

*This section is WIP.*

.. TODO
   Define DWARF register enumeration.

   If want to present a wavefront state then should expose vector registers as
   64 wide (rather than per work-item view that LLVM uses). Either as separate
   registers, or a 64x4 byte single register. In either case use a new LANE op
   (akin to XDREF) to select the current lane usage in a location
   expression. This would also allow scalar register spilling to vector register
   lanes to be expressed (currently no debug information is being generated for
   spilling). If choose a wide single register approach then use LANE in
   conjunction with PIECE operation to select the dword part of the register for
   the current lane. If the separate register approach then use LANE to select
   the register.

Source Text
~~~~~~~~~~~

*This section is WIP.*

.. TODO
   DWARF extension to include runtime generated source text.

.. _amdgpu-code-conventions:

Code Conventions
================

This section provides code conventions used for each supported target triple OS
(see :ref:`amdgpu-target-triples`).

AMDHSA
------

This section provides code conventions used when the target triple OS is
``amdhsa`` (see :ref:`amdgpu-target-triples`).

.. _amdgpu-amdhsa-hsa-code-object-metadata:

Code Object Metadata
~~~~~~~~~~~~~~~~~~~~

The code object metadata specifies extensible metadata associated with the code
objects executed on HSA [HSA]_ compatible runtimes such as AMD's ROCm
[AMD-ROCm]_. It is specified by the ``NT_AMD_AMDGPU_HSA_METADATA`` note record
(see :ref:`amdgpu-note-records`) and is required when the target triple OS is
``amdhsa`` (see :ref:`amdgpu-target-triples`). It must contain the minimum
information necessary to support the ROCM kernel queries. For example, the
segment sizes needed in a dispatch packet. In addition, a high level language
runtime may require other information to be included. For example, the AMD
OpenCL runtime records kernel argument information.

The metadata is specified as a YAML formatted string (see [YAML]_ and
:doc:`YamlIO`).

.. TODO
   Is the string null terminated? It probably should not if YAML allows it to
   contain null characters, otherwise it should be.

The metadata is represented as a single YAML document comprised of the mapping
defined in table :ref:`amdgpu-amdhsa-code-object-metadata-mapping-table` and
referenced tables.

For boolean values, the string values of ``false`` and ``true`` are used for
false and true respectively.

Additional information can be added to the mappings. To avoid conflicts, any
non-AMD key names should be prefixed by "*vendor-name*.".

  .. table:: AMDHSA Code Object Metadata Mapping
     :name: amdgpu-amdhsa-code-object-metadata-mapping-table

     ========== ============== ========= =======================================
     String Key Value Type     Required? Description
     ========== ============== ========= =======================================
     "Version"  sequence of    Required  - The first integer is the major
                2 integers                 version. Currently 1.
                                         - The second integer is the minor
                                           version. Currently 0.
     "Printf"   sequence of              Each string is encoded information
                strings                  about a printf function call. The
                                         encoded information is organized as
                                         fields separated by colon (':'):

                                         ``ID:N:S[0]:S[1]:...:S[N-1]:FormatString``

                                         where:

                                         ``ID``
                                           A 32 bit integer as a unique id for
                                           each printf function call

                                         ``N``
                                           A 32 bit integer equal to the number
                                           of arguments of printf function call
                                           minus 1

                                         ``S[i]`` (where i = 0, 1, ... , N-1)
                                           32 bit integers for the size in bytes
                                           of the i-th FormatString argument of
                                           the printf function call

                                         FormatString
                                           The format string passed to the
                                           printf function call.
     "Kernels"  sequence of    Required  Sequence of the mappings for each
                mapping                  kernel in the code object. See
                                         :ref:`amdgpu-amdhsa-code-object-kernel-metadata-mapping-table`
                                         for the definition of the mapping.
     ========== ============== ========= =======================================

..

  .. table:: AMDHSA Code Object Kernel Metadata Mapping
     :name: amdgpu-amdhsa-code-object-kernel-metadata-mapping-table

     ================= ============== ========= ================================
     String Key        Value Type     Required? Description
     ================= ============== ========= ================================
     "Name"            string         Required  Source name of the kernel.
     "SymbolName"      string         Required  Name of the kernel
                                                descriptor ELF symbol.
     "Language"        string                   Source language of the kernel.
                                                Values include:

                                                - "OpenCL C"
                                                - "OpenCL C++"
                                                - "HCC"
                                                - "OpenMP"

     "LanguageVersion" sequence of              - The first integer is the major
                       2 integers                 version.
                                                - The second integer is the
                                                  minor version.
     "Attrs"           mapping                  Mapping of kernel attributes.
                                                See
                                                :ref:`amdgpu-amdhsa-code-object-kernel-attribute-metadata-mapping-table`
                                                for the mapping definition.
     "Args"            sequence of              Sequence of mappings of the
                       mapping                  kernel arguments. See
                                                :ref:`amdgpu-amdhsa-code-object-kernel-argument-metadata-mapping-table`
                                                for the definition of the mapping.
     "CodeProps"       mapping                  Mapping of properties related to
                                                the kernel code. See
                                                :ref:`amdgpu-amdhsa-code-object-kernel-code-properties-metadata-mapping-table`
                                                for the mapping definition.
     ================= ============== ========= ================================

..

  .. table:: AMDHSA Code Object Kernel Attribute Metadata Mapping
     :name: amdgpu-amdhsa-code-object-kernel-attribute-metadata-mapping-table

     =================== ============== ========= ==============================
     String Key          Value Type     Required? Description
     =================== ============== ========= ==============================
     "ReqdWorkGroupSize" sequence of              If not 0, 0, 0 then all values
                         3 integers               must be >=1 and the dispatch
                                                  work-group size X, Y, Z must
                                                  correspond to the specified
                                                  values. Defaults to 0, 0, 0.

                                                  Corresponds to the OpenCL
                                                  ``reqd_work_group_size``
                                                  attribute.
     "WorkGroupSizeHint" sequence of              The dispatch work-group size
                         3 integers               X, Y, Z is likely to be the
                                                  specified values.

                                                  Corresponds to the OpenCL
                                                  ``work_group_size_hint``
                                                  attribute.
     "VecTypeHint"       string                   The name of a scalar or vector
                                                  type.

                                                  Corresponds to the OpenCL
                                                  ``vec_type_hint`` attribute.

     "RuntimeHandle"     string                   The external symbol name
                                                  associated with a kernel.
                                                  OpenCL runtime allocates a
                                                  global buffer for the symbol
                                                  and saves the kernel's address
                                                  to it, which is used for
                                                  device side enqueueing. Only
                                                  available for device side
                                                  enqueued kernels.
     =================== ============== ========= ==============================

..

  .. table:: AMDHSA Code Object Kernel Argument Metadata Mapping
     :name: amdgpu-amdhsa-code-object-kernel-argument-metadata-mapping-table

     ================= ============== ========= ================================
     String Key        Value Type     Required? Description
     ================= ============== ========= ================================
     "Name"            string                   Kernel argument name.
     "TypeName"        string                   Kernel argument type name.
     "Size"            integer        Required  Kernel argument size in bytes.
     "Align"           integer        Required  Kernel argument alignment in
                                                bytes. Must be a power of two.
     "ValueKind"       string         Required  Kernel argument kind that
                                                specifies how to set up the
                                                corresponding argument.
                                                Values include:

                                                "ByValue"
                                                  The argument is copied
                                                  directly into the kernarg.

                                                "GlobalBuffer"
                                                  A global address space pointer
                                                  to the buffer data is passed
                                                  in the kernarg.

                                                "DynamicSharedPointer"
                                                  A group address space pointer
                                                  to dynamically allocated LDS
                                                  is passed in the kernarg.

                                                "Sampler"
                                                  A global address space
                                                  pointer to a S# is passed in
                                                  the kernarg.

                                                "Image"
                                                  A global address space
                                                  pointer to a T# is passed in
                                                  the kernarg.

                                                "Pipe"
                                                  A global address space pointer
                                                  to an OpenCL pipe is passed in
                                                  the kernarg.

                                                "Queue"
                                                  A global address space pointer
                                                  to an OpenCL device enqueue
                                                  queue is passed in the
                                                  kernarg.

                                                "HiddenGlobalOffsetX"
                                                  The OpenCL grid dispatch
                                                  global offset for the X
                                                  dimension is passed in the
                                                  kernarg.

                                                "HiddenGlobalOffsetY"
                                                  The OpenCL grid dispatch
                                                  global offset for the Y
                                                  dimension is passed in the
                                                  kernarg.

                                                "HiddenGlobalOffsetZ"
                                                  The OpenCL grid dispatch
                                                  global offset for the Z
                                                  dimension is passed in the
                                                  kernarg.

                                                "HiddenNone"
                                                  An argument that is not used
                                                  by the kernel. Space needs to
                                                  be left for it, but it does
                                                  not need to be set up.

                                                "HiddenPrintfBuffer"
                                                  A global address space pointer
                                                  to the runtime printf buffer
                                                  is passed in kernarg.

                                                "HiddenDefaultQueue"
                                                  A global address space pointer
                                                  to the OpenCL device enqueue
                                                  queue that should be used by
                                                  the kernel by default is
                                                  passed in the kernarg.

                                                "HiddenCompletionAction"
                                                  A global address space pointer
                                                  to help link enqueued kernels into
                                                  the ancestor tree for determining
                                                  when the parent kernel has finished.

     "ValueType"       string         Required  Kernel argument value type. Only
                                                present if "ValueKind" is
                                                "ByValue". For vector data
                                                types, the value is for the
                                                element type. Values include:

                                                - "Struct"
                                                - "I8"
                                                - "U8"
                                                - "I16"
                                                - "U16"
                                                - "F16"
                                                - "I32"
                                                - "U32"
                                                - "F32"
                                                - "I64"
                                                - "U64"
                                                - "F64"

                                                .. TODO
                                                   How can it be determined if a
                                                   vector type, and what size
                                                   vector?
     "PointeeAlign"    integer                  Alignment in bytes of pointee
                                                type for pointer type kernel
                                                argument. Must be a power
                                                of 2. Only present if
                                                "ValueKind" is
                                                "DynamicSharedPointer".
     "AddrSpaceQual"   string                   Kernel argument address space
                                                qualifier. Only present if
                                                "ValueKind" is "GlobalBuffer" or
                                                "DynamicSharedPointer". Values
                                                are:

                                                - "Private"
                                                - "Global"
                                                - "Constant"
                                                - "Local"
                                                - "Generic"
                                                - "Region"

                                                .. TODO
                                                   Is GlobalBuffer only Global
                                                   or Constant? Is
                                                   DynamicSharedPointer always
                                                   Local? Can HCC allow Generic?
                                                   How can Private or Region
                                                   ever happen?
     "AccQual"         string                   Kernel argument access
                                                qualifier. Only present if
                                                "ValueKind" is "Image" or
                                                "Pipe". Values
                                                are:

                                                - "ReadOnly"
                                                - "WriteOnly"
                                                - "ReadWrite"

                                                .. TODO
                                                   Does this apply to
                                                   GlobalBuffer?
     "ActualAccQual"   string                   The actual memory accesses
                                                performed by the kernel on the
                                                kernel argument. Only present if
                                                "ValueKind" is "GlobalBuffer",
                                                "Image", or "Pipe". This may be
                                                more restrictive than indicated
                                                by "AccQual" to reflect what the
                                                kernel actual does. If not
                                                present then the runtime must
                                                assume what is implied by
                                                "AccQual" and "IsConst". Values
                                                are:

                                                - "ReadOnly"
                                                - "WriteOnly"
                                                - "ReadWrite"

     "IsConst"         boolean                  Indicates if the kernel argument
                                                is const qualified. Only present
                                                if "ValueKind" is
                                                "GlobalBuffer".

     "IsRestrict"      boolean                  Indicates if the kernel argument
                                                is restrict qualified. Only
                                                present if "ValueKind" is
                                                "GlobalBuffer".

     "IsVolatile"      boolean                  Indicates if the kernel argument
                                                is volatile qualified. Only
                                                present if "ValueKind" is
                                                "GlobalBuffer".

     "IsPipe"          boolean                  Indicates if the kernel argument
                                                is pipe qualified. Only present
                                                if "ValueKind" is "Pipe".

                                                .. TODO
                                                   Can GlobalBuffer be pipe
                                                   qualified?
     ================= ============== ========= ================================

..

  .. table:: AMDHSA Code Object Kernel Code Properties Metadata Mapping
     :name: amdgpu-amdhsa-code-object-kernel-code-properties-metadata-mapping-table

     ============================ ============== ========= =====================
     String Key                   Value Type     Required? Description
     ============================ ============== ========= =====================
     "KernargSegmentSize"         integer        Required  The size in bytes of
                                                           the kernarg segment
                                                           that holds the values
                                                           of the arguments to
                                                           the kernel.
     "GroupSegmentFixedSize"      integer        Required  The amount of group
                                                           segment memory
                                                           required by a
                                                           work-group in
                                                           bytes. This does not
                                                           include any
                                                           dynamically allocated
                                                           group segment memory
                                                           that may be added
                                                           when the kernel is
                                                           dispatched.
     "PrivateSegmentFixedSize"    integer        Required  The amount of fixed
                                                           private address space
                                                           memory required for a
                                                           work-item in
                                                           bytes. If the kernel
                                                           uses a dynamic call
                                                           stack then additional
                                                           space must be added
                                                           to this value for the
                                                           call stack.
     "KernargSegmentAlign"        integer        Required  The maximum byte
                                                           alignment of
                                                           arguments in the
                                                           kernarg segment. Must
                                                           be a power of 2.
     "WavefrontSize"              integer        Required  Wavefront size. Must
                                                           be a power of 2.
     "NumSGPRs"                   integer        Required  Number of scalar
                                                           registers used by a
                                                           wavefront for
                                                           GFX6-GFX9. This
                                                           includes the special
                                                           SGPRs for VCC, Flat
                                                           Scratch (GFX7-GFX9)
                                                           and XNACK (for
                                                           GFX8-GFX9). It does
                                                           not include the 16
                                                           SGPR added if a trap
                                                           handler is
                                                           enabled. It is not
                                                           rounded up to the
                                                           allocation
                                                           granularity.
     "NumVGPRs"                   integer        Required  Number of vector
                                                           registers used by
                                                           each work-item for
                                                           GFX6-GFX9
     "MaxFlatWorkGroupSize"       integer        Required  Maximum flat
                                                           work-group size
                                                           supported by the
                                                           kernel in work-items.
                                                           Must be >=1 and
                                                           consistent with
                                                           ReqdWorkGroupSize if
                                                           not 0, 0, 0.
     "NumSpilledSGPRs"            integer                  Number of stores from
                                                           a scalar register to
                                                           a register allocator
                                                           created spill
                                                           location.
     "NumSpilledVGPRs"            integer                  Number of stores from
                                                           a vector register to
                                                           a register allocator
                                                           created spill
                                                           location.
     ============================ ============== ========= =====================

..

Kernel Dispatch
~~~~~~~~~~~~~~~

The HSA architected queuing language (AQL) defines a user space memory interface
that can be used to control the dispatch of kernels, in an agent independent
way. An agent can have zero or more AQL queues created for it using the ROCm
runtime, in which AQL packets (all of which are 64 bytes) can be placed. See the
*HSA Platform System Architecture Specification* [HSA]_ for the AQL queue
mechanics and packet layouts.

The packet processor of a kernel agent is responsible for detecting and
dispatching HSA kernels from the AQL queues associated with it. For AMD GPUs the
packet processor is implemented by the hardware command processor (CP),
asynchronous dispatch controller (ADC) and shader processor input controller
(SPI).

The ROCm runtime can be used to allocate an AQL queue object. It uses the kernel
mode driver to initialize and register the AQL queue with CP.

To dispatch a kernel the following actions are performed. This can occur in the
CPU host program, or from an HSA kernel executing on a GPU.

1. A pointer to an AQL queue for the kernel agent on which the kernel is to be
   executed is obtained.
2. A pointer to the kernel descriptor (see
   :ref:`amdgpu-amdhsa-kernel-descriptor`) of the kernel to execute is
   obtained. It must be for a kernel that is contained in a code object that that
   was loaded by the ROCm runtime on the kernel agent with which the AQL queue is
   associated.
3. Space is allocated for the kernel arguments using the ROCm runtime allocator
   for a memory region with the kernarg property for the kernel agent that will
   execute the kernel. It must be at least 16 byte aligned.
4. Kernel argument values are assigned to the kernel argument memory
   allocation. The layout is defined in the *HSA Programmer's Language Reference*
   [HSA]_. For AMDGPU the kernel execution directly accesses the kernel argument
   memory in the same way constant memory is accessed. (Note that the HSA
   specification allows an implementation to copy the kernel argument contents to
   another location that is accessed by the kernel.)
5. An AQL kernel dispatch packet is created on the AQL queue. The ROCm runtime
   api uses 64 bit atomic operations to reserve space in the AQL queue for the
   packet. The packet must be set up, and the final write must use an atomic
   store release to set the packet kind to ensure the packet contents are
   visible to the kernel agent. AQL defines a doorbell signal mechanism to
   notify the kernel agent that the AQL queue has been updated. These rules, and
   the layout of the AQL queue and kernel dispatch packet is defined in the *HSA
   System Architecture Specification* [HSA]_.
6. A kernel dispatch packet includes information about the actual dispatch,
   such as grid and work-group size, together with information from the code
   object about the kernel, such as segment sizes. The ROCm runtime queries on
   the kernel symbol can be used to obtain the code object values which are
   recorded in the :ref:`amdgpu-amdhsa-hsa-code-object-metadata`.
7. CP executes micro-code and is responsible for detecting and setting up the
   GPU to execute the wavefronts of a kernel dispatch.
8. CP ensures that when the a wavefront starts executing the kernel machine
   code, the scalar general purpose registers (SGPR) and vector general purpose
   registers (VGPR) are set up as required by the machine code. The required
   setup is defined in the :ref:`amdgpu-amdhsa-kernel-descriptor`. The initial
   register state is defined in
   :ref:`amdgpu-amdhsa-initial-kernel-execution-state`.
9. The prolog of the kernel machine code (see
   :ref:`amdgpu-amdhsa-kernel-prolog`) sets up the machine state as necessary
   before continuing executing the machine code that corresponds to the kernel.
10. When the kernel dispatch has completed execution, CP signals the completion
    signal specified in the kernel dispatch packet if not 0.

.. _amdgpu-amdhsa-memory-spaces:

Memory Spaces
~~~~~~~~~~~~~

The memory space properties are:

  .. table:: AMDHSA Memory Spaces
     :name: amdgpu-amdhsa-memory-spaces-table

     ================= =========== ======== ======= ==================
     Memory Space Name HSA Segment Hardware Address NULL Value
                       Name        Name     Size
     ================= =========== ======== ======= ==================
     Private           private     scratch  32      0x00000000
     Local             group       LDS      32      0xFFFFFFFF
     Global            global      global   64      0x0000000000000000
     Constant          constant    *same as 64      0x0000000000000000
                                   global*
     Generic           flat        flat     64      0x0000000000000000
     Region            N/A         GDS      32      *not implemented
                                                    for AMDHSA*
     ================= =========== ======== ======= ==================

The global and constant memory spaces both use global virtual addresses, which
are the same virtual address space used by the CPU. However, some virtual
addresses may only be accessible to the CPU, some only accessible by the GPU,
and some by both.

Using the constant memory space indicates that the data will not change during
the execution of the kernel. This allows scalar read instructions to be
used. The vector and scalar L1 caches are invalidated of volatile data before
each kernel dispatch execution to allow constant memory to change values between
kernel dispatches.

The local memory space uses the hardware Local Data Store (LDS) which is
automatically allocated when the hardware creates work-groups of wavefronts, and
freed when all the wavefronts of a work-group have terminated. The data store
(DS) instructions can be used to access it.

The private memory space uses the hardware scratch memory support. If the kernel
uses scratch, then the hardware allocates memory that is accessed using
wavefront lane dword (4 byte) interleaving. The mapping used from private
address to physical address is:

  ``wavefront-scratch-base +
  (private-address * wavefront-size * 4) +
  (wavefront-lane-id * 4)``

There are different ways that the wavefront scratch base address is determined
by a wavefront (see :ref:`amdgpu-amdhsa-initial-kernel-execution-state`). This
memory can be accessed in an interleaved manner using buffer instruction with
the scratch buffer descriptor and per wave scratch offset, by the scratch
instructions, or by flat instructions. If each lane of a wavefront accesses the
same private address, the interleaving results in adjacent dwords being accessed
and hence requires fewer cache lines to be fetched. Multi-dword access is not
supported except by flat and scratch instructions in GFX9.

The generic address space uses the hardware flat address support available in
GFX7-GFX9. This uses two fixed ranges of virtual addresses (the private and
local appertures), that are outside the range of addressible global memory, to
map from a flat address to a private or local address.

FLAT instructions can take a flat address and access global, private (scratch)
and group (LDS) memory depending in if the address is within one of the
apperture ranges. Flat access to scratch requires hardware aperture setup and
setup in the kernel prologue (see :ref:`amdgpu-amdhsa-flat-scratch`). Flat
access to LDS requires hardware aperture setup and M0 (GFX7-GFX8) register setup
(see :ref:`amdgpu-amdhsa-m0`).

To convert between a segment address and a flat address the base address of the
appertures address can be used. For GFX7-GFX8 these are available in the
:ref:`amdgpu-amdhsa-hsa-aql-queue` the address of which can be obtained with
Queue Ptr SGPR (see :ref:`amdgpu-amdhsa-initial-kernel-execution-state`). For
GFX9 the appature base addresses are directly available as inline constant
registers ``SRC_SHARED_BASE/LIMIT`` and ``SRC_PRIVATE_BASE/LIMIT``. In 64 bit
address mode the apperture sizes are 2^32 bytes and the base is aligned to 2^32
which makes it easier to convert from flat to segment or segment to flat.

Image and Samplers
~~~~~~~~~~~~~~~~~~

Image and sample handles created by the ROCm runtime are 64 bit addresses of a
hardware 32 byte V# and 48 byte S# object respectively. In order to support the
HSA ``query_sampler`` operations two extra dwords are used to store the HSA BRIG
enumeration values for the queries that are not trivially deducible from the S#
representation.

HSA Signals
~~~~~~~~~~~

HSA signal handles created by the ROCm runtime are 64 bit addresses of a
structure allocated in memory accessible from both the CPU and GPU. The
structure is defined by the ROCm runtime and subject to change between releases
(see [AMD-ROCm-github]_).

.. _amdgpu-amdhsa-hsa-aql-queue:

HSA AQL Queue
~~~~~~~~~~~~~

The HSA AQL queue structure is defined by the ROCm runtime and subject to change
between releases (see [AMD-ROCm-github]_). For some processors it contains
fields needed to implement certain language features such as the flat address
aperture bases. It also contains fields used by CP such as managing the
allocation of scratch memory.

.. _amdgpu-amdhsa-kernel-descriptor:

Kernel Descriptor
~~~~~~~~~~~~~~~~~

A kernel descriptor consists of the information needed by CP to initiate the
execution of a kernel, including the entry point address of the machine code
that implements the kernel.

Kernel Descriptor for GFX6-GFX9
+++++++++++++++++++++++++++++++

CP microcode requires the Kernel descritor to be allocated on 64 byte alignment.

  .. table:: Kernel Descriptor for GFX6-GFX9
     :name: amdgpu-amdhsa-kernel-descriptor-gfx6-gfx9-table

     ======= ======= =============================== ============================
     Bits    Size    Field Name                      Description
     ======= ======= =============================== ============================
     31:0    4 bytes GroupSegmentFixedSize           The amount of fixed local
                                                     address space memory
                                                     required for a work-group
                                                     in bytes. This does not
                                                     include any dynamically
                                                     allocated local address
                                                     space memory that may be
                                                     added when the kernel is
                                                     dispatched.
     63:32   4 bytes PrivateSegmentFixedSize         The amount of fixed
                                                     private address space
                                                     memory required for a
                                                     work-item in bytes. If
                                                     is_dynamic_callstack is 1
                                                     then additional space must
                                                     be added to this value for
                                                     the call stack.
     127:64  8 bytes                                 Reserved, must be 0.
     191:128 8 bytes KernelCodeEntryByteOffset       Byte offset (possibly
                                                     negative) from base
                                                     address of kernel
                                                     descriptor to kernel's
                                                     entry point instruction
                                                     which must be 256 byte
                                                     aligned.
     383:192 24                                      Reserved, must be 0.
             bytes
     415:384 4 bytes ComputePgmRsrc1                 Compute Shader (CS)
                                                     program settings used by
                                                     CP to set up
                                                     ``COMPUTE_PGM_RSRC1``
                                                     configuration
                                                     register. See
                                                     :ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx9-table`.
     447:416 4 bytes ComputePgmRsrc2                 Compute Shader (CS)
                                                     program settings used by
                                                     CP to set up
                                                     ``COMPUTE_PGM_RSRC2``
                                                     configuration
                                                     register. See
                                                     :ref:`amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx9-table`.
     448     1 bit   EnableSGPRPrivateSegmentBuffer  Enable the setup of the
                                                     SGPR user data registers
                                                     (see
                                                     :ref:`amdgpu-amdhsa-initial-kernel-execution-state`).

                                                     The total number of SGPR
                                                     user data registers
                                                     requested must not exceed
                                                     16 and match value in
                                                     ``compute_pgm_rsrc2.user_sgpr.user_sgpr_count``.
                                                     Any requests beyond 16
                                                     will be ignored.
     449     1 bit   EnableSGPRDispatchPtr           *see above*
     450     1 bit   EnableSGPRQueuePtr              *see above*
     451     1 bit   EnableSGPRKernargSegmentPtr     *see above*
     452     1 bit   EnableSGPRDispatchID            *see above*
     453     1 bit   EnableSGPRFlatScratchInit       *see above*
     454     1 bit   EnableSGPRPrivateSegmentSize    *see above*
     455     1 bit   EnableSGPRGridWorkgroupCountX   Not implemented in CP and
                                                     should always be 0.
     456     1 bit   EnableSGPRGridWorkgroupCountY   Not implemented in CP and
                                                     should always be 0.
     457     1 bit   EnableSGPRGridWorkgroupCountZ   Not implemented in CP and
                                                     should always be 0.
     463:458 6 bits                                  Reserved, must be 0.
     511:464 6                                       Reserved, must be 0.
             bytes
     512     **Total size 64 bytes.**
     ======= ====================================================================

..

  .. table:: compute_pgm_rsrc1 for GFX6-GFX9
     :name: amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx9-table

     ======= ======= =============================== ===========================================================================
     Bits    Size    Field Name                      Description
     ======= ======= =============================== ===========================================================================
     5:0     6 bits  GRANULATED_WORKITEM_VGPR_COUNT  Number of vector registers
                                                     used by each work-item,
                                                     granularity is device
                                                     specific:

                                                     GFX6-GFX9
                                                       - max_vgpr 1..256
                                                       - roundup((max_vgpg + 1)
                                                         / 4) - 1

                                                     Used by CP to set up
                                                     ``COMPUTE_PGM_RSRC1.VGPRS``.
     9:6     4 bits  GRANULATED_WAVEFRONT_SGPR_COUNT Number of scalar registers
                                                     used by a wavefront,
                                                     granularity is device
                                                     specific:

                                                     GFX6-GFX8
                                                       - max_sgpr 1..112
                                                       - roundup((max_sgpg + 1)
                                                         / 8) - 1
                                                     GFX9
                                                       - max_sgpr 1..112
                                                       - roundup((max_sgpg + 1)
                                                         / 16) - 1

                                                     Includes the special SGPRs
                                                     for VCC, Flat Scratch (for
                                                     GFX7 onwards) and XNACK
                                                     (for GFX8 onwards). It does
                                                     not include the 16 SGPR
                                                     added if a trap handler is
                                                     enabled.

                                                     Used by CP to set up
                                                     ``COMPUTE_PGM_RSRC1.SGPRS``.
     11:10   2 bits  PRIORITY                        Must be 0.

                                                     Start executing wavefront
                                                     at the specified priority.

                                                     CP is responsible for
                                                     filling in
                                                     ``COMPUTE_PGM_RSRC1.PRIORITY``.
     13:12   2 bits  FLOAT_ROUND_MODE_32             Wavefront starts execution
                                                     with specified rounding
                                                     mode for single (32
                                                     bit) floating point
                                                     precision floating point
                                                     operations.

                                                     Floating point rounding
                                                     mode values are defined in
                                                     :ref:`amdgpu-amdhsa-floating-point-rounding-mode-enumeration-values-table`.

                                                     Used by CP to set up
                                                     ``COMPUTE_PGM_RSRC1.FLOAT_MODE``.
     15:14   2 bits  FLOAT_ROUND_MODE_16_64          Wavefront starts execution
                                                     with specified rounding
                                                     denorm mode for half/double (16
                                                     and 64 bit) floating point
                                                     precision floating point
                                                     operations.

                                                     Floating point rounding
                                                     mode values are defined in
                                                     :ref:`amdgpu-amdhsa-floating-point-rounding-mode-enumeration-values-table`.

                                                     Used by CP to set up
                                                     ``COMPUTE_PGM_RSRC1.FLOAT_MODE``.
     17:16   2 bits  FLOAT_DENORM_MODE_32            Wavefront starts execution
                                                     with specified denorm mode
                                                     for single (32
                                                     bit)  floating point
                                                     precision floating point
                                                     operations.

                                                     Floating point denorm mode
                                                     values are defined in
                                                     :ref:`amdgpu-amdhsa-floating-point-denorm-mode-enumeration-values-table`.

                                                     Used by CP to set up
                                                     ``COMPUTE_PGM_RSRC1.FLOAT_MODE``.
     19:18   2 bits  FLOAT_DENORM_MODE_16_64         Wavefront starts execution
                                                     with specified denorm mode
                                                     for half/double (16
                                                     and 64 bit) floating point
                                                     precision floating point
                                                     operations.

                                                     Floating point denorm mode
                                                     values are defined in
                                                     :ref:`amdgpu-amdhsa-floating-point-denorm-mode-enumeration-values-table`.

                                                     Used by CP to set up
                                                     ``COMPUTE_PGM_RSRC1.FLOAT_MODE``.
     20      1 bit   PRIV                            Must be 0.

                                                     Start executing wavefront
                                                     in privilege trap handler
                                                     mode.

                                                     CP is responsible for
                                                     filling in
                                                     ``COMPUTE_PGM_RSRC1.PRIV``.
     21      1 bit   ENABLE_DX10_CLAMP               Wavefront starts execution
                                                     with DX10 clamp mode
                                                     enabled. Used by the vector
                                                     ALU to force DX10 style
                                                     treatment of NaN's (when
                                                     set, clamp NaN to zero,
                                                     otherwise pass NaN
                                                     through).

                                                     Used by CP to set up
                                                     ``COMPUTE_PGM_RSRC1.DX10_CLAMP``.
     22      1 bit   DEBUG_MODE                      Must be 0.

                                                     Start executing wavefront
                                                     in single step mode.

                                                     CP is responsible for
                                                     filling in
                                                     ``COMPUTE_PGM_RSRC1.DEBUG_MODE``.
     23      1 bit   ENABLE_IEEE_MODE                Wavefront starts execution
                                                     with IEEE mode
                                                     enabled. Floating point
                                                     opcodes that support
                                                     exception flag gathering
                                                     will quiet and propagate
                                                     signaling-NaN inputs per
                                                     IEEE 754-2008. Min_dx10 and
                                                     max_dx10 become IEEE
                                                     754-2008 compliant due to
                                                     signaling-NaN propagation
                                                     and quieting.

                                                     Used by CP to set up
                                                     ``COMPUTE_PGM_RSRC1.IEEE_MODE``.
     24      1 bit   BULKY                           Must be 0.

                                                     Only one work-group allowed
                                                     to execute on a compute
                                                     unit.

                                                     CP is responsible for
                                                     filling in
                                                     ``COMPUTE_PGM_RSRC1.BULKY``.
     25      1 bit   CDBG_USER                       Must be 0.

                                                     Flag that can be used to
                                                     control debugging code.

                                                     CP is responsible for
                                                     filling in
                                                     ``COMPUTE_PGM_RSRC1.CDBG_USER``.
     26      1 bit   FP16_OVFL                       GFX6-GFX8
                                                       Reserved, must be 0.
                                                     GFX9
                                                       Wavefront starts execution
                                                       with specified fp16 overflow
                                                       mode.

                                                       - If 0, fp16 overflow generates
                                                         +/-INF values.
                                                       - If 1, fp16 overflow that is the
                                                         result of an +/-INF input value
                                                         or divide by 0 produces a +/-INF,
                                                         otherwise clamps computed
                                                         overflow to +/-MAX_FP16 as
                                                         appropriate.

                                                       Used by CP to set up
                                                       ``COMPUTE_PGM_RSRC1.FP16_OVFL``.
     31:27   5 bits                                  Reserved, must be 0.
     32      **Total size 4 bytes**
     ======= ===================================================================================================================

..

  .. table:: compute_pgm_rsrc2 for GFX6-GFX9
     :name: amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx9-table

     ======= ======= =============================== ===========================================================================
     Bits    Size    Field Name                      Description
     ======= ======= =============================== ===========================================================================
     0       1 bit   ENABLE_SGPR_PRIVATE_SEGMENT     Enable the setup of the
                     _WAVE_OFFSET                    SGPR wave scratch offset
                                                     system register (see
                                                     :ref:`amdgpu-amdhsa-initial-kernel-execution-state`).

                                                     Used by CP to set up
                                                     ``COMPUTE_PGM_RSRC2.SCRATCH_EN``.
     5:1     5 bits  USER_SGPR_COUNT                 The total number of SGPR
                                                     user data registers
                                                     requested. This number must
                                                     match the number of user
                                                     data registers enabled.

                                                     Used by CP to set up
                                                     ``COMPUTE_PGM_RSRC2.USER_SGPR``.
     6       1 bit   ENABLE_TRAP_HANDLER             Set to 1 if code contains a
                                                     TRAP instruction which
                                                     requires a trap handler to
                                                     be enabled.

                                                     CP sets
                                                     ``COMPUTE_PGM_RSRC2.TRAP_PRESENT``
                                                     if the runtime has
                                                     installed a trap handler
                                                     regardless of the setting
                                                     of this field.
     7       1 bit   ENABLE_SGPR_WORKGROUP_ID_X      Enable the setup of the
                                                     system SGPR register for
                                                     the work-group id in the X
                                                     dimension (see
                                                     :ref:`amdgpu-amdhsa-initial-kernel-execution-state`).

                                                     Used by CP to set up
                                                     ``COMPUTE_PGM_RSRC2.TGID_X_EN``.
     8       1 bit   ENABLE_SGPR_WORKGROUP_ID_Y      Enable the setup of the
                                                     system SGPR register for
                                                     the work-group id in the Y
                                                     dimension (see
                                                     :ref:`amdgpu-amdhsa-initial-kernel-execution-state`).

                                                     Used by CP to set up
                                                     ``COMPUTE_PGM_RSRC2.TGID_Y_EN``.
     9       1 bit   ENABLE_SGPR_WORKGROUP_ID_Z      Enable the setup of the
                                                     system SGPR register for
                                                     the work-group id in the Z
                                                     dimension (see
                                                     :ref:`amdgpu-amdhsa-initial-kernel-execution-state`).

                                                     Used by CP to set up
                                                     ``COMPUTE_PGM_RSRC2.TGID_Z_EN``.
     10      1 bit   ENABLE_SGPR_WORKGROUP_INFO      Enable the setup of the
                                                     system SGPR register for
                                                     work-group information (see
                                                     :ref:`amdgpu-amdhsa-initial-kernel-execution-state`).

                                                     Used by CP to set up
                                                     ``COMPUTE_PGM_RSRC2.TGID_SIZE_EN``.
     12:11   2 bits  ENABLE_VGPR_WORKITEM_ID         Enable the setup of the
                                                     VGPR system registers used
                                                     for the work-item ID.
                                                     :ref:`amdgpu-amdhsa-system-vgpr-work-item-id-enumeration-values-table`
                                                     defines the values.

                                                     Used by CP to set up
                                                     ``COMPUTE_PGM_RSRC2.TIDIG_CMP_CNT``.
     13      1 bit   ENABLE_EXCEPTION_ADDRESS_WATCH  Must be 0.

                                                     Wavefront starts execution
                                                     with address watch
                                                     exceptions enabled which
                                                     are generated when L1 has
                                                     witnessed a thread access
                                                     an *address of
                                                     interest*.

                                                     CP is responsible for
                                                     filling in the address
                                                     watch bit in
                                                     ``COMPUTE_PGM_RSRC2.EXCP_EN_MSB``
                                                     according to what the
                                                     runtime requests.
     14      1 bit   ENABLE_EXCEPTION_MEMORY         Must be 0.

                                                     Wavefront starts execution
                                                     with memory violation
                                                     exceptions exceptions
                                                     enabled which are generated
                                                     when a memory violation has
                                                     occurred for this wave from
                                                     L1 or LDS
                                                     (write-to-read-only-memory,
                                                     mis-aligned atomic, LDS
                                                     address out of range,
                                                     illegal address, etc.).

                                                     CP sets the memory
                                                     violation bit in
                                                     ``COMPUTE_PGM_RSRC2.EXCP_EN_MSB``
                                                     according to what the
                                                     runtime requests.
     23:15   9 bits  GRANULATED_LDS_SIZE             Must be 0.

                                                     CP uses the rounded value
                                                     from the dispatch packet,
                                                     not this value, as the
                                                     dispatch may contain
                                                     dynamically allocated group
                                                     segment memory. CP writes
                                                     directly to
                                                     ``COMPUTE_PGM_RSRC2.LDS_SIZE``.

                                                     Amount of group segment
                                                     (LDS) to allocate for each
                                                     work-group. Granularity is
                                                     device specific:

                                                     GFX6:
                                                       roundup(lds-size / (64 * 4))
                                                     GFX7-GFX9:
                                                       roundup(lds-size / (128 * 4))

     24      1 bit   ENABLE_EXCEPTION_IEEE_754_FP    Wavefront starts execution
                     _INVALID_OPERATION              with specified exceptions
                                                     enabled.

                                                     Used by CP to set up
                                                     ``COMPUTE_PGM_RSRC2.EXCP_EN``
                                                     (set from bits 0..6).

                                                     IEEE 754 FP Invalid
                                                     Operation
     25      1 bit   ENABLE_EXCEPTION_FP_DENORMAL    FP Denormal one or more
                     _SOURCE                         input operands is a
                                                     denormal number
     26      1 bit   ENABLE_EXCEPTION_IEEE_754_FP    IEEE 754 FP Division by
                     _DIVISION_BY_ZERO               Zero
     27      1 bit   ENABLE_EXCEPTION_IEEE_754_FP    IEEE 754 FP FP Overflow
                     _OVERFLOW
     28      1 bit   ENABLE_EXCEPTION_IEEE_754_FP    IEEE 754 FP Underflow
                     _UNDERFLOW
     29      1 bit   ENABLE_EXCEPTION_IEEE_754_FP    IEEE 754 FP Inexact
                     _INEXACT
     30      1 bit   ENABLE_EXCEPTION_INT_DIVIDE_BY  Integer Division by Zero
                     _ZERO                           (rcp_iflag_f32 instruction
                                                     only)
     31      1 bit                                   Reserved, must be 0.
     32      **Total size 4 bytes.**
     ======= ===================================================================================================================

..

  .. table:: Floating Point Rounding Mode Enumeration Values
     :name: amdgpu-amdhsa-floating-point-rounding-mode-enumeration-values-table

     ====================================== ===== ==============================
     Enumeration Name                       Value Description
     ====================================== ===== ==============================
     AMDGPU_FLOAT_ROUND_MODE_NEAR_EVEN      0     Round Ties To Even
     AMDGPU_FLOAT_ROUND_MODE_PLUS_INFINITY  1     Round Toward +infinity
     AMDGPU_FLOAT_ROUND_MODE_MINUS_INFINITY 2     Round Toward -infinity
     AMDGPU_FLOAT_ROUND_MODE_ZERO           3     Round Toward 0
     ====================================== ===== ==============================

..

  .. table:: Floating Point Denorm Mode Enumeration Values
     :name: amdgpu-amdhsa-floating-point-denorm-mode-enumeration-values-table

     ====================================== ===== ==============================
     Enumeration Name                       Value Description
     ====================================== ===== ==============================
     AMDGPU_FLOAT_DENORM_MODE_FLUSH_SRC_DST 0     Flush Source and Destination
                                                  Denorms
     AMDGPU_FLOAT_DENORM_MODE_FLUSH_DST     1     Flush Output Denorms
     AMDGPU_FLOAT_DENORM_MODE_FLUSH_SRC     2     Flush Source Denorms
     AMDGPU_FLOAT_DENORM_MODE_FLUSH_NONE    3     No Flush
     ====================================== ===== ==============================

..

  .. table:: System VGPR Work-Item ID Enumeration Values
     :name: amdgpu-amdhsa-system-vgpr-work-item-id-enumeration-values-table

     ======================================== ===== ============================
     Enumeration Name                         Value Description
     ======================================== ===== ============================
     AMDGPU_SYSTEM_VGPR_WORKITEM_ID_X         0     Set work-item X dimension
                                                    ID.
     AMDGPU_SYSTEM_VGPR_WORKITEM_ID_X_Y       1     Set work-item X and Y
                                                    dimensions ID.
     AMDGPU_SYSTEM_VGPR_WORKITEM_ID_X_Y_Z     2     Set work-item X, Y and Z
                                                    dimensions ID.
     AMDGPU_SYSTEM_VGPR_WORKITEM_ID_UNDEFINED 3     Undefined.
     ======================================== ===== ============================

.. _amdgpu-amdhsa-initial-kernel-execution-state:

Initial Kernel Execution State
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This section defines the register state that will be set up by the packet
processor prior to the start of execution of every wavefront. This is limited by
the constraints of the hardware controllers of CP/ADC/SPI.

The order of the SGPR registers is defined, but the compiler can specify which
ones are actually setup in the kernel descriptor using the ``enable_sgpr_*`` bit
fields (see :ref:`amdgpu-amdhsa-kernel-descriptor`). The register numbers used
for enabled registers are dense starting at SGPR0: the first enabled register is
SGPR0, the next enabled register is SGPR1 etc.; disabled registers do not have
an SGPR number.

The initial SGPRs comprise up to 16 User SRGPs that are set by CP and apply to
all waves of the grid. It is possible to specify more than 16 User SGPRs using
the ``enable_sgpr_*`` bit fields, in which case only the first 16 are actually
initialized. These are then immediately followed by the System SGPRs that are
set up by ADC/SPI and can have different values for each wave of the grid
dispatch.

SGPR register initial state is defined in
:ref:`amdgpu-amdhsa-sgpr-register-set-up-order-table`.

  .. table:: SGPR Register Set Up Order
     :name: amdgpu-amdhsa-sgpr-register-set-up-order-table

     ========== ========================== ====== ==============================
     SGPR Order Name                       Number Description
                (kernel descriptor enable  of
                field)                     SGPRs
     ========== ========================== ====== ==============================
     First      Private Segment Buffer     4      V# that can be used, together
                (enable_sgpr_private              with Scratch Wave Offset as an
                _segment_buffer)                  offset, to access the private
                                                  memory space using a segment
                                                  address.

                                                  CP uses the value provided by
                                                  the runtime.
     then       Dispatch Ptr               2      64 bit address of AQL dispatch
                (enable_sgpr_dispatch_ptr)        packet for kernel dispatch
                                                  actually executing.
     then       Queue Ptr                  2      64 bit address of amd_queue_t
                (enable_sgpr_queue_ptr)           object for AQL queue on which
                                                  the dispatch packet was
                                                  queued.
     then       Kernarg Segment Ptr        2      64 bit address of Kernarg
                (enable_sgpr_kernarg              segment. This is directly
                _segment_ptr)                     copied from the
                                                  kernarg_address in the kernel
                                                  dispatch packet.

                                                  Having CP load it once avoids
                                                  loading it at the beginning of
                                                  every wavefront.
     then       Dispatch Id                2      64 bit Dispatch ID of the
                (enable_sgpr_dispatch_id)         dispatch packet being
                                                  executed.
     then       Flat Scratch Init          2      This is 2 SGPRs:
                (enable_sgpr_flat_scratch
                _init)                            GFX6
                                                    Not supported.
                                                  GFX7-GFX8
                                                    The first SGPR is a 32 bit
                                                    byte offset from
                                                    ``SH_HIDDEN_PRIVATE_BASE_VIMID``
                                                    to per SPI base of memory
                                                    for scratch for the queue
                                                    executing the kernel
                                                    dispatch. CP obtains this
                                                    from the runtime. (The
                                                    Scratch Segment Buffer base
                                                    address is
                                                    ``SH_HIDDEN_PRIVATE_BASE_VIMID``
                                                    plus this offset.) The value
                                                    of Scratch Wave Offset must
                                                    be added to this offset by
                                                    the kernel machine code,
                                                    right shifted by 8, and
                                                    moved to the FLAT_SCRATCH_HI
                                                    SGPR register.
                                                    FLAT_SCRATCH_HI corresponds
                                                    to SGPRn-4 on GFX7, and
                                                    SGPRn-6 on GFX8 (where SGPRn
                                                    is the highest numbered SGPR
                                                    allocated to the wave).
                                                    FLAT_SCRATCH_HI is
                                                    multiplied by 256 (as it is
                                                    in units of 256 bytes) and
                                                    added to
                                                    ``SH_HIDDEN_PRIVATE_BASE_VIMID``
                                                    to calculate the per wave
                                                    FLAT SCRATCH BASE in flat
                                                    memory instructions that
                                                    access the scratch
                                                    apperture.

                                                    The second SGPR is 32 bit
                                                    byte size of a single
                                                    work-item's scratch memory
                                                    usage. CP obtains this from
                                                    the runtime, and it is
                                                    always a multiple of DWORD.
                                                    CP checks that the value in
                                                    the kernel dispatch packet
                                                    Private Segment Byte Size is
                                                    not larger, and requests the
                                                    runtime to increase the
                                                    queue's scratch size if
                                                    necessary. The kernel code
                                                    must move it to
                                                    FLAT_SCRATCH_LO which is
                                                    SGPRn-3 on GFX7 and SGPRn-5
                                                    on GFX8. FLAT_SCRATCH_LO is
                                                    used as the FLAT SCRATCH
                                                    SIZE in flat memory
                                                    instructions. Having CP load
                                                    it once avoids loading it at
                                                    the beginning of every
                                                    wavefront.
                                                  GFX9
                                                    This is the
                                                    64 bit base address of the
                                                    per SPI scratch backing
                                                    memory managed by SPI for
                                                    the queue executing the
                                                    kernel dispatch. CP obtains
                                                    this from the runtime (and
                                                    divides it if there are
                                                    multiple Shader Arrays each
                                                    with its own SPI). The value
                                                    of Scratch Wave Offset must
                                                    be added by the kernel
                                                    machine code and the result
                                                    moved to the FLAT_SCRATCH
                                                    SGPR which is SGPRn-6 and
                                                    SGPRn-5. It is used as the
                                                    FLAT SCRATCH BASE in flat
                                                    memory instructions.
     then       Private Segment Size       1      The 32 bit byte size of a
                                                  (enable_sgpr_private single
                                                  work-item's
                                                  scratch_segment_size) memory
                                                  allocation. This is the
                                                  value from the kernel
                                                  dispatch packet Private
                                                  Segment Byte Size rounded up
                                                  by CP to a multiple of
                                                  DWORD.

                                                  Having CP load it once avoids
                                                  loading it at the beginning of
                                                  every wavefront.

                                                  This is not used for
                                                  GFX7-GFX8 since it is the same
                                                  value as the second SGPR of
                                                  Flat Scratch Init. However, it
                                                  may be needed for GFX9 which
                                                  changes the meaning of the
                                                  Flat Scratch Init value.
     then       Grid Work-Group Count X    1      32 bit count of the number of
                (enable_sgpr_grid                 work-groups in the X dimension
                _workgroup_count_X)               for the grid being
                                                  executed. Computed from the
                                                  fields in the kernel dispatch
                                                  packet as ((grid_size.x +
                                                  workgroup_size.x - 1) /
                                                  workgroup_size.x).
     then       Grid Work-Group Count Y    1      32 bit count of the number of
                (enable_sgpr_grid                 work-groups in the Y dimension
                _workgroup_count_Y &&             for the grid being
                less than 16 previous             executed. Computed from the
                SGPRs)                            fields in the kernel dispatch
                                                  packet as ((grid_size.y +
                                                  workgroup_size.y - 1) /
                                                  workgroupSize.y).

                                                  Only initialized if <16
                                                  previous SGPRs initialized.
     then       Grid Work-Group Count Z    1      32 bit count of the number of
                (enable_sgpr_grid                 work-groups in the Z dimension
                _workgroup_count_Z &&             for the grid being
                less than 16 previous             executed. Computed from the
                SGPRs)                            fields in the kernel dispatch
                                                  packet as ((grid_size.z +
                                                  workgroup_size.z - 1) /
                                                  workgroupSize.z).

                                                  Only initialized if <16
                                                  previous SGPRs initialized.
     then       Work-Group Id X            1      32 bit work-group id in X
                (enable_sgpr_workgroup_id         dimension of grid for
                _X)                               wavefront.
     then       Work-Group Id Y            1      32 bit work-group id in Y
                (enable_sgpr_workgroup_id         dimension of grid for
                _Y)                               wavefront.
     then       Work-Group Id Z            1      32 bit work-group id in Z
                (enable_sgpr_workgroup_id         dimension of grid for
                _Z)                               wavefront.
     then       Work-Group Info            1      {first_wave, 14'b0000,
                (enable_sgpr_workgroup            ordered_append_term[10:0],
                _info)                            threadgroup_size_in_waves[5:0]}
     then       Scratch Wave Offset        1      32 bit byte offset from base
                (enable_sgpr_private              of scratch base of queue
                _segment_wave_offset)             executing the kernel
                                                  dispatch. Must be used as an
                                                  offset with Private
                                                  segment address when using
                                                  Scratch Segment Buffer. It
                                                  must be used to set up FLAT
                                                  SCRATCH for flat addressing
                                                  (see
                                                  :ref:`amdgpu-amdhsa-flat-scratch`).
     ========== ========================== ====== ==============================

The order of the VGPR registers is defined, but the compiler can specify which
ones are actually setup in the kernel descriptor using the ``enable_vgpr*`` bit
fields (see :ref:`amdgpu-amdhsa-kernel-descriptor`). The register numbers used
for enabled registers are dense starting at VGPR0: the first enabled register is
VGPR0, the next enabled register is VGPR1 etc.; disabled registers do not have a
VGPR number.

VGPR register initial state is defined in
:ref:`amdgpu-amdhsa-vgpr-register-set-up-order-table`.

  .. table:: VGPR Register Set Up Order
     :name: amdgpu-amdhsa-vgpr-register-set-up-order-table

     ========== ========================== ====== ==============================
     VGPR Order Name                       Number Description
                (kernel descriptor enable  of
                field)                     VGPRs
     ========== ========================== ====== ==============================
     First      Work-Item Id X             1      32 bit work item id in X
                (Always initialized)              dimension of work-group for
                                                  wavefront lane.
     then       Work-Item Id Y             1      32 bit work item id in Y
                (enable_vgpr_workitem_id          dimension of work-group for
                > 0)                              wavefront lane.
     then       Work-Item Id Z             1      32 bit work item id in Z
                (enable_vgpr_workitem_id          dimension of work-group for
                > 1)                              wavefront lane.
     ========== ========================== ====== ==============================

The setting of registers is is done by GPU CP/ADC/SPI hardware as follows:

1. SGPRs before the Work-Group Ids are set by CP using the 16 User Data
   registers.
2. Work-group Id registers X, Y, Z are set by ADC which supports any
   combination including none.
3. Scratch Wave Offset is set by SPI in a per wave basis which is why its value
   cannot included with the flat scratch init value which is per queue.
4. The VGPRs are set by SPI which only supports specifying either (X), (X, Y)
   or (X, Y, Z).

Flat Scratch register pair are adjacent SGRRs so they can be moved as a 64 bit
value to the hardware required SGPRn-3 and SGPRn-4 respectively.

The global segment can be accessed either using buffer instructions (GFX6 which
has V# 64 bit address support), flat instructions (GFX7-GFX9), or global
instructions (GFX9).

If buffer operations are used then the compiler can generate a V# with the
following properties:

* base address of 0
* no swizzle
* ATC: 1 if IOMMU present (such as APU)
* ptr64: 1
* MTYPE set to support memory coherence that matches the runtime (such as CC for
  APU and NC for dGPU).

.. _amdgpu-amdhsa-kernel-prolog:

Kernel Prolog
~~~~~~~~~~~~~

.. _amdgpu-amdhsa-m0:

M0
++

GFX6-GFX8
  The M0 register must be initialized with a value at least the total LDS size
  if the kernel may access LDS via DS or flat operations. Total LDS size is
  available in dispatch packet. For M0, it is also possible to use maximum
  possible value of LDS for given target (0x7FFF for GFX6 and 0xFFFF for
  GFX7-GFX8).
GFX9
  The M0 register is not used for range checking LDS accesses and so does not
  need to be initialized in the prolog.

.. _amdgpu-amdhsa-flat-scratch:

Flat Scratch
++++++++++++

If the kernel may use flat operations to access scratch memory, the prolog code
must set up FLAT_SCRATCH register pair (FLAT_SCRATCH_LO/FLAT_SCRATCH_HI which
are in SGPRn-4/SGPRn-3). Initialization uses Flat Scratch Init and Scratch Wave
Offset SGPR registers (see :ref:`amdgpu-amdhsa-initial-kernel-execution-state`):

GFX6
  Flat scratch is not supported.

GFX7-GFX8
  1. The low word of Flat Scratch Init is 32 bit byte offset from
     ``SH_HIDDEN_PRIVATE_BASE_VIMID`` to the base of scratch backing memory
     being managed by SPI for the queue executing the kernel dispatch. This is
     the same value used in the Scratch Segment Buffer V# base address. The
     prolog must add the value of Scratch Wave Offset to get the wave's byte
     scratch backing memory offset from ``SH_HIDDEN_PRIVATE_BASE_VIMID``. Since
     FLAT_SCRATCH_LO is in units of 256 bytes, the offset must be right shifted
     by 8 before moving into FLAT_SCRATCH_LO.
  2. The second word of Flat Scratch Init is 32 bit byte size of a single
     work-items scratch memory usage. This is directly loaded from the kernel
     dispatch packet Private Segment Byte Size and rounded up to a multiple of
     DWORD. Having CP load it once avoids loading it at the beginning of every
     wavefront. The prolog must move it to FLAT_SCRATCH_LO for use as FLAT SCRATCH
     SIZE.

GFX9
  The Flat Scratch Init is the 64 bit address of the base of scratch backing
  memory being managed by SPI for the queue executing the kernel dispatch. The
  prolog must add the value of Scratch Wave Offset and moved to the FLAT_SCRATCH
  pair for use as the flat scratch base in flat memory instructions.

.. _amdgpu-amdhsa-memory-model:

Memory Model
~~~~~~~~~~~~

This section describes the mapping of LLVM memory model onto AMDGPU machine code
(see :ref:`memmodel`). *The implementation is WIP.*

.. TODO
   Update when implementation complete.

The AMDGPU backend supports the memory synchronization scopes specified in
:ref:`amdgpu-memory-scopes`.

The code sequences used to implement the memory model are defined in table
:ref:`amdgpu-amdhsa-memory-model-code-sequences-gfx6-gfx9-table`.

The sequences specify the order of instructions that a single thread must
execute. The ``s_waitcnt`` and ``buffer_wbinvl1_vol`` are defined with respect
to other memory instructions executed by the same thread. This allows them to be
moved earlier or later which can allow them to be combined with other instances
of the same instruction, or hoisted/sunk out of loops to improve
performance. Only the instructions related to the memory model are given;
additional ``s_waitcnt`` instructions are required to ensure registers are
defined before being used. These may be able to be combined with the memory
model ``s_waitcnt`` instructions as described above.

The AMDGPU backend supports the following memory models:

  HSA Memory Model [HSA]_
    The HSA memory model uses a single happens-before relation for all address
    spaces (see :ref:`amdgpu-address-spaces`).
  OpenCL Memory Model [OpenCL]_
    The OpenCL memory model which has separate happens-before relations for the
    global and local address spaces. Only a fence specifying both global and
    local address space, and seq_cst instructions join the relationships. Since
    the LLVM ``memfence`` instruction does not allow an address space to be
    specified the OpenCL fence has to convervatively assume both local and
    global address space was specified. However, optimizations can often be
    done to eliminate the additional ``s_waitcnt`` instructions when there are
    no intervening memory instructions which access the corresponding address
    space. The code sequences in the table indicate what can be omitted for the
    OpenCL memory. The target triple environment is used to determine if the
    source language is OpenCL (see :ref:`amdgpu-opencl`).

``ds/flat_load/store/atomic`` instructions to local memory are termed LDS
operations.

``buffer/global/flat_load/store/atomic`` instructions to global memory are
termed vector memory operations.

For GFX6-GFX9:

* Each agent has multiple compute units (CU).
* Each CU has multiple SIMDs that execute wavefronts.
* The wavefronts for a single work-group are executed in the same CU but may be
  executed by different SIMDs.
* Each CU has a single LDS memory shared by the wavefronts of the work-groups
  executing on it.
* All LDS operations of a CU are performed as wavefront wide operations in a
  global order and involve no caching. Completion is reported to a wavefront in
  execution order.
* The LDS memory has multiple request queues shared by the SIMDs of a
  CU. Therefore, the LDS operations performed by different waves of a work-group
  can be reordered relative to each other, which can result in reordering the
  visibility of vector memory operations with respect to LDS operations of other
  wavefronts in the same work-group. A ``s_waitcnt lgkmcnt(0)`` is required to
  ensure synchronization between LDS operations and vector memory operations
  between waves of a work-group, but not between operations performed by the
  same wavefront.
* The vector memory operations are performed as wavefront wide operations and
  completion is reported to a wavefront in execution order. The exception is
  that for GFX7-GFX9 ``flat_load/store/atomic`` instructions can report out of
  vector memory order if they access LDS memory, and out of LDS operation order
  if they access global memory.
* The vector memory operations access a single vector L1 cache shared by all
  SIMDs a CU. Therefore, no special action is required for coherence between the
  lanes of a single wavefront, or for coherence between wavefronts in the same
  work-group. A ``buffer_wbinvl1_vol`` is required for coherence between waves
  executing in different work-groups as they may be executing on different CUs.
* The scalar memory operations access a scalar L1 cache shared by all wavefronts
  on a group of CUs. The scalar and vector L1 caches are not coherent. However,
  scalar operations are used in a restricted way so do not impact the memory
  model. See :ref:`amdgpu-amdhsa-memory-spaces`.
* The vector and scalar memory operations use an L2 cache shared by all CUs on
  the same agent.
* The L2 cache has independent channels to service disjoint ranges of virtual
  addresses.
* Each CU has a separate request queue per channel. Therefore, the vector and
  scalar memory operations performed by waves executing in different work-groups
  (which may be executing on different CUs) of an agent can be reordered
  relative to each other. A ``s_waitcnt vmcnt(0)`` is required to ensure
  synchronization between vector memory operations of different CUs. It ensures a
  previous vector memory operation has completed before executing a subsequent
  vector memory or LDS operation and so can be used to meet the requirements of
  acquire and release.
* The L2 cache can be kept coherent with other agents on some targets, or ranges
  of virtual addresses can be set up to bypass it to ensure system coherence.

Private address space uses ``buffer_load/store`` using the scratch V# (GFX6-GFX8),
or ``scratch_load/store`` (GFX9). Since only a single thread is accessing the
memory, atomic memory orderings are not meaningful and all accesses are treated
as non-atomic.

Constant address space uses ``buffer/global_load`` instructions (or equivalent
scalar memory instructions). Since the constant address space contents do not
change during the execution of a kernel dispatch it is not legal to perform
stores, and atomic memory orderings are not meaningful and all access are
treated as non-atomic.

A memory synchronization scope wider than work-group is not meaningful for the
group (LDS) address space and is treated as work-group.

The memory model does not support the region address space which is treated as
non-atomic.

Acquire memory ordering is not meaningful on store atomic instructions and is
treated as non-atomic.

Release memory ordering is not meaningful on load atomic instructions and is
treated a non-atomic.

Acquire-release memory ordering is not meaningful on load or store atomic
instructions and is treated as acquire and release respectively.

AMDGPU backend only uses scalar memory operations to access memory that is
proven to not change during the execution of the kernel dispatch. This includes
constant address space and global address space for program scope const
variables. Therefore the kernel machine code does not have to maintain the
scalar L1 cache to ensure it is coherent with the vector L1 cache. The scalar
and vector L1 caches are invalidated between kernel dispatches by CP since
constant address space data may change between kernel dispatch executions. See
:ref:`amdgpu-amdhsa-memory-spaces`.

The one execption is if scalar writes are used to spill SGPR registers. In this
case the AMDGPU backend ensures the memory location used to spill is never
accessed by vector memory operations at the same time. If scalar writes are used
then a ``s_dcache_wb`` is inserted before the ``s_endpgm`` and before a function
return since the locations may be used for vector memory instructions by a
future wave that uses the same scratch area, or a function call that creates a
frame at the same address, respectively. There is no need for a ``s_dcache_inv``
as all scalar writes are write-before-read in the same thread.

Scratch backing memory (which is used for the private address space)
is accessed with MTYPE NC_NV (non-coherenent non-volatile). Since the private
address space is only accessed by a single thread, and is always
write-before-read, there is never a need to invalidate these entries from the L1
cache. Hence all cache invalidates are done as ``*_vol`` to only invalidate the
volatile cache lines.

On dGPU the kernarg backing memory is accessed as UC (uncached) to avoid needing
to invalidate the L2 cache. This also causes it to be treated as
non-volatile and so is not invalidated by ``*_vol``. On APU it is accessed as CC
(cache coherent) and so the L2 cache will coherent with the CPU and other
agents.

  .. table:: AMDHSA Memory Model Code Sequences GFX6-GFX9
     :name: amdgpu-amdhsa-memory-model-code-sequences-gfx6-gfx9-table

     ============ ============ ============== ========== ===============================
     LLVM Instr   LLVM Memory  LLVM Memory    AMDGPU     AMDGPU Machine Code
                  Ordering     Sync Scope     Address
                                              Space
     ============ ============ ============== ========== ===============================
     **Non-Atomic**
     -----------------------------------------------------------------------------------
     load         *none*       *none*         - global   - !volatile & !nontemporal
                                              - generic
                                              - private    1. buffer/global/flat_load
                                              - constant
                                                         - volatile & !nontemporal

                                                           1. buffer/global/flat_load
                                                              glc=1

                                                         - nontemporal

                                                           1. buffer/global/flat_load
                                                              glc=1 slc=1

     load         *none*       *none*         - local    1. ds_load
     store        *none*       *none*         - global   - !nontemporal
                                              - generic
                                              - private    1. buffer/global/flat_store
                                              - constant
                                                         - nontemporal

                                                           1. buffer/global/flat_stote
                                                              glc=1 slc=1

     store        *none*       *none*         - local    1. ds_store
     **Unordered Atomic**
     -----------------------------------------------------------------------------------
     load atomic  unordered    *any*          *any*      *Same as non-atomic*.
     store atomic unordered    *any*          *any*      *Same as non-atomic*.
     atomicrmw    unordered    *any*          *any*      *Same as monotonic
                                                         atomic*.
     **Monotonic Atomic**
     -----------------------------------------------------------------------------------
     load atomic  monotonic    - singlethread - global   1. buffer/global/flat_load
                               - wavefront    - generic
                               - workgroup
     load atomic  monotonic    - singlethread - local    1. ds_load
                               - wavefront
                               - workgroup
     load atomic  monotonic    - agent        - global   1. buffer/global/flat_load
                               - system       - generic     glc=1
     store atomic monotonic    - singlethread - global   1. buffer/global/flat_store
                               - wavefront    - generic
                               - workgroup
                               - agent
                               - system
     store atomic monotonic    - singlethread - local    1. ds_store
                               - wavefront
                               - workgroup
     atomicrmw    monotonic    - singlethread - global   1. buffer/global/flat_atomic
                               - wavefront    - generic
                               - workgroup
                               - agent
                               - system
     atomicrmw    monotonic    - singlethread - local    1. ds_atomic
                               - wavefront
                               - workgroup
     **Acquire Atomic**
     -----------------------------------------------------------------------------------
     load atomic  acquire      - singlethread - global   1. buffer/global/ds/flat_load
                               - wavefront    - local
                                              - generic
     load atomic  acquire      - workgroup    - global   1. buffer/global/flat_load
     load atomic  acquire      - workgroup    - local    1. ds_load
                                                         2. s_waitcnt lgkmcnt(0)

                                                           - If OpenCL, omit.
                                                           - Must happen before
                                                             any following
                                                             global/generic
                                                             load/load
                                                             atomic/store/store
                                                             atomic/atomicrmw.
                                                           - Ensures any
                                                             following global
                                                             data read is no
                                                             older than the load
                                                             atomic value being
                                                             acquired.
     load atomic  acquire      - workgroup    - generic  1. flat_load
                                                         2. s_waitcnt lgkmcnt(0)

                                                           - If OpenCL, omit.
                                                           - Must happen before
                                                             any following
                                                             global/generic
                                                             load/load
                                                             atomic/store/store
                                                             atomic/atomicrmw.
                                                           - Ensures any
                                                             following global
                                                             data read is no
                                                             older than the load
                                                             atomic value being
                                                             acquired.
     load atomic  acquire      - agent        - global   1. buffer/global/flat_load
                               - system                     glc=1
                                                         2. s_waitcnt vmcnt(0)

                                                           - Must happen before
                                                             following
                                                             buffer_wbinvl1_vol.
                                                           - Ensures the load
                                                             has completed
                                                             before invalidating
                                                             the cache.

                                                         3. buffer_wbinvl1_vol

                                                           - Must happen before
                                                             any following
                                                             global/generic
                                                             load/load
                                                             atomic/atomicrmw.
                                                           - Ensures that
                                                             following
                                                             loads will not see
                                                             stale global data.

     load atomic  acquire      - agent        - generic  1. flat_load glc=1
                               - system                  2. s_waitcnt vmcnt(0) &
                                                            lgkmcnt(0)

                                                           - If OpenCL omit
                                                             lgkmcnt(0).
                                                           - Must happen before
                                                             following
                                                             buffer_wbinvl1_vol.
                                                           - Ensures the flat_load
                                                             has completed
                                                             before invalidating
                                                             the cache.

                                                         3. buffer_wbinvl1_vol

                                                           - Must happen before
                                                             any following
                                                             global/generic
                                                             load/load
                                                             atomic/atomicrmw.
                                                           - Ensures that
                                                             following loads
                                                             will not see stale
                                                             global data.

     atomicrmw    acquire      - singlethread - global   1. buffer/global/ds/flat_atomic
                               - wavefront    - local
                                              - generic
     atomicrmw    acquire      - workgroup    - global   1. buffer/global/flat_atomic
     atomicrmw    acquire      - workgroup    - local    1. ds_atomic
                                                         2. waitcnt lgkmcnt(0)

                                                           - If OpenCL, omit.
                                                           - Must happen before
                                                             any following
                                                             global/generic
                                                             load/load
                                                             atomic/store/store
                                                             atomic/atomicrmw.
                                                           - Ensures any
                                                             following global
                                                             data read is no
                                                             older than the
                                                             atomicrmw value
                                                             being acquired.

     atomicrmw    acquire      - workgroup    - generic  1. flat_atomic
                                                         2. waitcnt lgkmcnt(0)

                                                           - If OpenCL, omit.
                                                           - Must happen before
                                                             any following
                                                             global/generic
                                                             load/load
                                                             atomic/store/store
                                                             atomic/atomicrmw.
                                                           - Ensures any
                                                             following global
                                                             data read is no
                                                             older than the
                                                             atomicrmw value
                                                             being acquired.

     atomicrmw    acquire      - agent        - global   1. buffer/global/flat_atomic
                               - system                  2. s_waitcnt vmcnt(0)

                                                           - Must happen before
                                                             following
                                                             buffer_wbinvl1_vol.
                                                           - Ensures the
                                                             atomicrmw has
                                                             completed before
                                                             invalidating the
                                                             cache.

                                                         3. buffer_wbinvl1_vol

                                                           - Must happen before
                                                             any following
                                                             global/generic
                                                             load/load
                                                             atomic/atomicrmw.
                                                           - Ensures that
                                                             following loads
                                                             will not see stale
                                                             global data.

     atomicrmw    acquire      - agent        - generic  1. flat_atomic
                               - system                  2. s_waitcnt vmcnt(0) &
                                                            lgkmcnt(0)

                                                           - If OpenCL, omit
                                                             lgkmcnt(0).
                                                           - Must happen before
                                                             following
                                                             buffer_wbinvl1_vol.
                                                           - Ensures the
                                                             atomicrmw has
                                                             completed before
                                                             invalidating the
                                                             cache.

                                                         3. buffer_wbinvl1_vol

                                                           - Must happen before
                                                             any following
                                                             global/generic
                                                             load/load
                                                             atomic/atomicrmw.
                                                           - Ensures that
                                                             following loads
                                                             will not see stale
                                                             global data.

     fence        acquire      - singlethread *none*     *none*
                               - wavefront
     fence        acquire      - workgroup    *none*     1. s_waitcnt lgkmcnt(0)

                                                           - If OpenCL and
                                                             address space is
                                                             not generic, omit.
                                                           - However, since LLVM
                                                             currently has no
                                                             address space on
                                                             the fence need to
                                                             conservatively
                                                             always generate. If
                                                             fence had an
                                                             address space then
                                                             set to address
                                                             space of OpenCL
                                                             fence flag, or to
                                                             generic if both
                                                             local and global
                                                             flags are
                                                             specified.
                                                           - Must happen after
                                                             any preceding
                                                             local/generic load
                                                             atomic/atomicrmw
                                                             with an equal or
                                                             wider sync scope
                                                             and memory ordering
                                                             stronger than
                                                             unordered (this is
                                                             termed the
                                                             fence-paired-atomic).
                                                           - Must happen before
                                                             any following
                                                             global/generic
                                                             load/load
                                                             atomic/store/store
                                                             atomic/atomicrmw.
                                                           - Ensures any
                                                             following global
                                                             data read is no
                                                             older than the
                                                             value read by the
                                                             fence-paired-atomic.

     fence        acquire      - agent        *none*     1. s_waitcnt lgkmcnt(0) &
                               - system                     vmcnt(0)

                                                           - If OpenCL and
                                                             address space is
                                                             not generic, omit
                                                             lgkmcnt(0).
                                                           - However, since LLVM
                                                             currently has no
                                                             address space on
                                                             the fence need to
                                                             conservatively
                                                             always generate
                                                             (see comment for
                                                             previous fence).
                                                           - Could be split into
                                                             separate s_waitcnt
                                                             vmcnt(0) and
                                                             s_waitcnt
                                                             lgkmcnt(0) to allow
                                                             them to be
                                                             independently moved
                                                             according to the
                                                             following rules.
                                                           - s_waitcnt vmcnt(0)
                                                             must happen after
                                                             any preceding
                                                             global/generic load
                                                             atomic/atomicrmw
                                                             with an equal or
                                                             wider sync scope
                                                             and memory ordering
                                                             stronger than
                                                             unordered (this is
                                                             termed the
                                                             fence-paired-atomic).
                                                           - s_waitcnt lgkmcnt(0)
                                                             must happen after
                                                             any preceding
                                                             local/generic load
                                                             atomic/atomicrmw
                                                             with an equal or
                                                             wider sync scope
                                                             and memory ordering
                                                             stronger than
                                                             unordered (this is
                                                             termed the
                                                             fence-paired-atomic).
                                                           - Must happen before
                                                             the following
                                                             buffer_wbinvl1_vol.
                                                           - Ensures that the
                                                             fence-paired atomic
                                                             has completed
                                                             before invalidating
                                                             the
                                                             cache. Therefore
                                                             any following
                                                             locations read must
                                                             be no older than
                                                             the value read by
                                                             the
                                                             fence-paired-atomic.

                                                         2. buffer_wbinvl1_vol

                                                           - Must happen before any
                                                             following global/generic
                                                             load/load
                                                             atomic/store/store
                                                             atomic/atomicrmw.
                                                           - Ensures that
                                                             following loads
                                                             will not see stale
                                                             global data.

     **Release Atomic**
     -----------------------------------------------------------------------------------
     store atomic release      - singlethread - global   1. buffer/global/ds/flat_store
                               - wavefront    - local
                                              - generic
     store atomic release      - workgroup    - global   1. s_waitcnt lgkmcnt(0)

                                                           - If OpenCL, omit.
                                                           - Must happen after
                                                             any preceding
                                                             local/generic
                                                             load/store/load
                                                             atomic/store
                                                             atomic/atomicrmw.
                                                           - Must happen before
                                                             the following
                                                             store.
                                                           - Ensures that all
                                                             memory operations
                                                             to local have
                                                             completed before
                                                             performing the
                                                             store that is being
                                                             released.

                                                         2. buffer/global/flat_store
     store atomic release      - workgroup    - local    1. ds_store
     store atomic release      - workgroup    - generic  1. s_waitcnt lgkmcnt(0)

                                                           - If OpenCL, omit.
                                                           - Must happen after
                                                             any preceding
                                                             local/generic
                                                             load/store/load
                                                             atomic/store
                                                             atomic/atomicrmw.
                                                           - Must happen before
                                                             the following
                                                             store.
                                                           - Ensures that all
                                                             memory operations
                                                             to local have
                                                             completed before
                                                             performing the
                                                             store that is being
                                                             released.

                                                         2. flat_store
     store atomic release      - agent        - global   1. s_waitcnt lgkmcnt(0) &
                               - system       - generic     vmcnt(0)

                                                           - If OpenCL, omit
                                                             lgkmcnt(0).
                                                           - Could be split into
                                                             separate s_waitcnt
                                                             vmcnt(0) and
                                                             s_waitcnt
                                                             lgkmcnt(0) to allow
                                                             them to be
                                                             independently moved
                                                             according to the
                                                             following rules.
                                                           - s_waitcnt vmcnt(0)
                                                             must happen after
                                                             any preceding
                                                             global/generic
                                                             load/store/load
                                                             atomic/store
                                                             atomic/atomicrmw.
                                                           - s_waitcnt lgkmcnt(0)
                                                             must happen after
                                                             any preceding
                                                             local/generic
                                                             load/store/load
                                                             atomic/store
                                                             atomic/atomicrmw.
                                                           - Must happen before
                                                             the following
                                                             store.
                                                           - Ensures that all
                                                             memory operations
                                                             to memory have
                                                             completed before
                                                             performing the
                                                             store that is being
                                                             released.

                                                         2. buffer/global/ds/flat_store
     atomicrmw    release      - singlethread - global   1. buffer/global/ds/flat_atomic
                               - wavefront    - local
                                              - generic
     atomicrmw    release      - workgroup    - global   1. s_waitcnt lgkmcnt(0)

                                                           - If OpenCL, omit.
                                                           - Must happen after
                                                             any preceding
                                                             local/generic
                                                             load/store/load
                                                             atomic/store
                                                             atomic/atomicrmw.
                                                           - Must happen before
                                                             the following
                                                             atomicrmw.
                                                           - Ensures that all
                                                             memory operations
                                                             to local have
                                                             completed before
                                                             performing the
                                                             atomicrmw that is
                                                             being released.

                                                         2. buffer/global/flat_atomic
     atomicrmw    release      - workgroup    - local    1. ds_atomic
     atomicrmw    release      - workgroup    - generic  1. s_waitcnt lgkmcnt(0)

                                                           - If OpenCL, omit.
                                                           - Must happen after
                                                             any preceding
                                                             local/generic
                                                             load/store/load
                                                             atomic/store
                                                             atomic/atomicrmw.
                                                           - Must happen before
                                                             the following
                                                             atomicrmw.
                                                           - Ensures that all
                                                             memory operations
                                                             to local have
                                                             completed before
                                                             performing the
                                                             atomicrmw that is
                                                             being released.

                                                         2. flat_atomic
     atomicrmw    release      - agent        - global   1. s_waitcnt lgkmcnt(0) &
                               - system       - generic     vmcnt(0)

                                                           - If OpenCL, omit
                                                             lgkmcnt(0).
                                                           - Could be split into
                                                             separate s_waitcnt
                                                             vmcnt(0) and
                                                             s_waitcnt
                                                             lgkmcnt(0) to allow
                                                             them to be
                                                             independently moved
                                                             according to the
                                                             following rules.
                                                           - s_waitcnt vmcnt(0)
                                                             must happen after
                                                             any preceding
                                                             global/generic
                                                             load/store/load
                                                             atomic/store
                                                             atomic/atomicrmw.
                                                           - s_waitcnt lgkmcnt(0)
                                                             must happen after
                                                             any preceding
                                                             local/generic
                                                             load/store/load
                                                             atomic/store
                                                             atomic/atomicrmw.
                                                           - Must happen before
                                                             the following
                                                             atomicrmw.
                                                           - Ensures that all
                                                             memory operations
                                                             to global and local
                                                             have completed
                                                             before performing
                                                             the atomicrmw that
                                                             is being released.

                                                         2. buffer/global/ds/flat_atomic
     fence        release      - singlethread *none*     *none*
                               - wavefront
     fence        release      - workgroup    *none*     1. s_waitcnt lgkmcnt(0)

                                                           - If OpenCL and
                                                             address space is
                                                             not generic, omit.
                                                           - However, since LLVM
                                                             currently has no
                                                             address space on
                                                             the fence need to
                                                             conservatively
                                                             always generate. If
                                                             fence had an
                                                             address space then
                                                             set to address
                                                             space of OpenCL
                                                             fence flag, or to
                                                             generic if both
                                                             local and global
                                                             flags are
                                                             specified.
                                                           - Must happen after
                                                             any preceding
                                                             local/generic
                                                             load/load
                                                             atomic/store/store
                                                             atomic/atomicrmw.
                                                           - Must happen before
                                                             any following store
                                                             atomic/atomicrmw
                                                             with an equal or
                                                             wider sync scope
                                                             and memory ordering
                                                             stronger than
                                                             unordered (this is
                                                             termed the
                                                             fence-paired-atomic).
                                                           - Ensures that all
                                                             memory operations
                                                             to local have
                                                             completed before
                                                             performing the
                                                             following
                                                             fence-paired-atomic.

     fence        release      - agent        *none*     1. s_waitcnt lgkmcnt(0) &
                               - system                     vmcnt(0)

                                                           - If OpenCL and
                                                             address space is
                                                             not generic, omit
                                                             lgkmcnt(0).
                                                           - If OpenCL and
                                                             address space is
                                                             local, omit
                                                             vmcnt(0).
                                                           - However, since LLVM
                                                             currently has no
                                                             address space on
                                                             the fence need to
                                                             conservatively
                                                             always generate. If
                                                             fence had an
                                                             address space then
                                                             set to address
                                                             space of OpenCL
                                                             fence flag, or to
                                                             generic if both
                                                             local and global
                                                             flags are
                                                             specified.
                                                           - Could be split into
                                                             separate s_waitcnt
                                                             vmcnt(0) and
                                                             s_waitcnt
                                                             lgkmcnt(0) to allow
                                                             them to be
                                                             independently moved
                                                             according to the
                                                             following rules.
                                                           - s_waitcnt vmcnt(0)
                                                             must happen after
                                                             any preceding
                                                             global/generic
                                                             load/store/load
                                                             atomic/store
                                                             atomic/atomicrmw.
                                                           - s_waitcnt lgkmcnt(0)
                                                             must happen after
                                                             any preceding
                                                             local/generic
                                                             load/store/load
                                                             atomic/store
                                                             atomic/atomicrmw.
                                                           - Must happen before
                                                             any following store
                                                             atomic/atomicrmw
                                                             with an equal or
                                                             wider sync scope
                                                             and memory ordering
                                                             stronger than
                                                             unordered (this is
                                                             termed the
                                                             fence-paired-atomic).
                                                           - Ensures that all
                                                             memory operations
                                                             have
                                                             completed before
                                                             performing the
                                                             following
                                                             fence-paired-atomic.

     **Acquire-Release Atomic**
     -----------------------------------------------------------------------------------
     atomicrmw    acq_rel      - singlethread - global   1. buffer/global/ds/flat_atomic
                               - wavefront    - local
                                              - generic
     atomicrmw    acq_rel      - workgroup    - global   1. s_waitcnt lgkmcnt(0)

                                                           - If OpenCL, omit.
                                                           - Must happen after
                                                             any preceding
                                                             local/generic
                                                             load/store/load
                                                             atomic/store
                                                             atomic/atomicrmw.
                                                           - Must happen before
                                                             the following
                                                             atomicrmw.
                                                           - Ensures that all
                                                             memory operations
                                                             to local have
                                                             completed before
                                                             performing the
                                                             atomicrmw that is
                                                             being released.

                                                         2. buffer/global/flat_atomic
     atomicrmw    acq_rel      - workgroup    - local    1. ds_atomic
                                                         2. s_waitcnt lgkmcnt(0)

                                                           - If OpenCL, omit.
                                                           - Must happen before
                                                             any following
                                                             global/generic
                                                             load/load
                                                             atomic/store/store
                                                             atomic/atomicrmw.
                                                           - Ensures any
                                                             following global
                                                             data read is no
                                                             older than the load
                                                             atomic value being
                                                             acquired.

     atomicrmw    acq_rel      - workgroup    - generic  1. s_waitcnt lgkmcnt(0)

                                                           - If OpenCL, omit.
                                                           - Must happen after
                                                             any preceding
                                                             local/generic
                                                             load/store/load
                                                             atomic/store
                                                             atomic/atomicrmw.
                                                           - Must happen before
                                                             the following
                                                             atomicrmw.
                                                           - Ensures that all
                                                             memory operations
                                                             to local have
                                                             completed before
                                                             performing the
                                                             atomicrmw that is
                                                             being released.

                                                         2. flat_atomic
                                                         3. s_waitcnt lgkmcnt(0)

                                                           - If OpenCL, omit.
                                                           - Must happen before
                                                             any following
                                                             global/generic
                                                             load/load
                                                             atomic/store/store
                                                             atomic/atomicrmw.
                                                           - Ensures any
                                                             following global
                                                             data read is no
                                                             older than the load
                                                             atomic value being
                                                             acquired.

     atomicrmw    acq_rel      - agent        - global   1. s_waitcnt lgkmcnt(0) &
                               - system                     vmcnt(0)

                                                           - If OpenCL, omit
                                                             lgkmcnt(0).
                                                           - Could be split into
                                                             separate s_waitcnt
                                                             vmcnt(0) and
                                                             s_waitcnt
                                                             lgkmcnt(0) to allow
                                                             them to be
                                                             independently moved
                                                             according to the
                                                             following rules.
                                                           - s_waitcnt vmcnt(0)
                                                             must happen after
                                                             any preceding
                                                             global/generic
                                                             load/store/load
                                                             atomic/store
                                                             atomic/atomicrmw.
                                                           - s_waitcnt lgkmcnt(0)
                                                             must happen after
                                                             any preceding
                                                             local/generic
                                                             load/store/load
                                                             atomic/store
                                                             atomic/atomicrmw.
                                                           - Must happen before
                                                             the following
                                                             atomicrmw.
                                                           - Ensures that all
                                                             memory operations
                                                             to global have
                                                             completed before
                                                             performing the
                                                             atomicrmw that is
                                                             being released.

                                                         2. buffer/global/flat_atomic
                                                         3. s_waitcnt vmcnt(0)

                                                           - Must happen before
                                                             following
                                                             buffer_wbinvl1_vol.
                                                           - Ensures the
                                                             atomicrmw has
                                                             completed before
                                                             invalidating the
                                                             cache.

                                                         4. buffer_wbinvl1_vol

                                                           - Must happen before
                                                             any following
                                                             global/generic
                                                             load/load
                                                             atomic/atomicrmw.
                                                           - Ensures that
                                                             following loads
                                                             will not see stale
                                                             global data.

     atomicrmw    acq_rel      - agent        - generic  1. s_waitcnt lgkmcnt(0) &
                               - system                     vmcnt(0)

                                                           - If OpenCL, omit
                                                             lgkmcnt(0).
                                                           - Could be split into
                                                             separate s_waitcnt
                                                             vmcnt(0) and
                                                             s_waitcnt
                                                             lgkmcnt(0) to allow
                                                             them to be
                                                             independently moved
                                                             according to the
                                                             following rules.
                                                           - s_waitcnt vmcnt(0)
                                                             must happen after
                                                             any preceding
                                                             global/generic
                                                             load/store/load
                                                             atomic/store
                                                             atomic/atomicrmw.
                                                           - s_waitcnt lgkmcnt(0)
                                                             must happen after
                                                             any preceding
                                                             local/generic
                                                             load/store/load
                                                             atomic/store
                                                             atomic/atomicrmw.
                                                           - Must happen before
                                                             the following
                                                             atomicrmw.
                                                           - Ensures that all
                                                             memory operations
                                                             to global have
                                                             completed before
                                                             performing the
                                                             atomicrmw that is
                                                             being released.

                                                         2. flat_atomic
                                                         3. s_waitcnt vmcnt(0) &
                                                            lgkmcnt(0)

                                                           - If OpenCL, omit
                                                             lgkmcnt(0).
                                                           - Must happen before
                                                             following
                                                             buffer_wbinvl1_vol.
                                                           - Ensures the
                                                             atomicrmw has
                                                             completed before
                                                             invalidating the
                                                             cache.

                                                         4. buffer_wbinvl1_vol

                                                           - Must happen before
                                                             any following
                                                             global/generic
                                                             load/load
                                                             atomic/atomicrmw.
                                                           - Ensures that
                                                             following loads
                                                             will not see stale
                                                             global data.

     fence        acq_rel      - singlethread *none*     *none*
                               - wavefront
     fence        acq_rel      - workgroup    *none*     1. s_waitcnt lgkmcnt(0)

                                                           - If OpenCL and
                                                             address space is
                                                             not generic, omit.
                                                           - However,
                                                             since LLVM
                                                             currently has no
                                                             address space on
                                                             the fence need to
                                                             conservatively
                                                             always generate
                                                             (see comment for
                                                             previous fence).
                                                           - Must happen after
                                                             any preceding
                                                             local/generic
                                                             load/load
                                                             atomic/store/store
                                                             atomic/atomicrmw.
                                                           - Must happen before
                                                             any following
                                                             global/generic
                                                             load/load
                                                             atomic/store/store
                                                             atomic/atomicrmw.
                                                           - Ensures that all
                                                             memory operations
                                                             to local have
                                                             completed before
                                                             performing any
                                                             following global
                                                             memory operations.
                                                           - Ensures that the
                                                             preceding
                                                             local/generic load
                                                             atomic/atomicrmw
                                                             with an equal or
                                                             wider sync scope
                                                             and memory ordering
                                                             stronger than
                                                             unordered (this is
                                                             termed the
                                                             acquire-fence-paired-atomic
                                                             ) has completed
                                                             before following
                                                             global memory
                                                             operations. This
                                                             satisfies the
                                                             requirements of
                                                             acquire.
                                                           - Ensures that all
                                                             previous memory
                                                             operations have
                                                             completed before a
                                                             following
                                                             local/generic store
                                                             atomic/atomicrmw
                                                             with an equal or
                                                             wider sync scope
                                                             and memory ordering
                                                             stronger than
                                                             unordered (this is
                                                             termed the
                                                             release-fence-paired-atomic
                                                             ). This satisfies the
                                                             requirements of
                                                             release.

     fence        acq_rel      - agent        *none*     1. s_waitcnt lgkmcnt(0) &
                               - system                     vmcnt(0)

                                                           - If OpenCL and
                                                             address space is
                                                             not generic, omit
                                                             lgkmcnt(0).
                                                           - However, since LLVM
                                                             currently has no
                                                             address space on
                                                             the fence need to
                                                             conservatively
                                                             always generate
                                                             (see comment for
                                                             previous fence).
                                                           - Could be split into
                                                             separate s_waitcnt
                                                             vmcnt(0) and
                                                             s_waitcnt
                                                             lgkmcnt(0) to allow
                                                             them to be
                                                             independently moved
                                                             according to the
                                                             following rules.
                                                           - s_waitcnt vmcnt(0)
                                                             must happen after
                                                             any preceding
                                                             global/generic
                                                             load/store/load
                                                             atomic/store
                                                             atomic/atomicrmw.
                                                           - s_waitcnt lgkmcnt(0)
                                                             must happen after
                                                             any preceding
                                                             local/generic
                                                             load/store/load
                                                             atomic/store
                                                             atomic/atomicrmw.
                                                           - Must happen before
                                                             the following
                                                             buffer_wbinvl1_vol.
                                                           - Ensures that the
                                                             preceding
                                                             global/local/generic
                                                             load
                                                             atomic/atomicrmw
                                                             with an equal or
                                                             wider sync scope
                                                             and memory ordering
                                                             stronger than
                                                             unordered (this is
                                                             termed the
                                                             acquire-fence-paired-atomic
                                                             ) has completed
                                                             before invalidating
                                                             the cache. This
                                                             satisfies the
                                                             requirements of
                                                             acquire.
                                                           - Ensures that all
                                                             previous memory
                                                             operations have
                                                             completed before a
                                                             following
                                                             global/local/generic
                                                             store
                                                             atomic/atomicrmw
                                                             with an equal or
                                                             wider sync scope
                                                             and memory ordering
                                                             stronger than
                                                             unordered (this is
                                                             termed the
                                                             release-fence-paired-atomic
                                                             ). This satisfies the
                                                             requirements of
                                                             release.

                                                         2. buffer_wbinvl1_vol

                                                           - Must happen before
                                                             any following
                                                             global/generic
                                                             load/load
                                                             atomic/store/store
                                                             atomic/atomicrmw.
                                                           - Ensures that
                                                             following loads
                                                             will not see stale
                                                             global data. This
                                                             satisfies the
                                                             requirements of
                                                             acquire.

     **Sequential Consistent Atomic**
     -----------------------------------------------------------------------------------
     load atomic  seq_cst      - singlethread - global   *Same as corresponding
                               - wavefront    - local    load atomic acquire,
                                              - generic  except must generated
                                                         all instructions even
                                                         for OpenCL.*
     load atomic  seq_cst      - workgroup    - global   1. s_waitcnt lgkmcnt(0)
                                              - generic
                                                           - Must
                                                             happen after
                                                             preceding
                                                             global/generic load
                                                             atomic/store
                                                             atomic/atomicrmw
                                                             with memory
                                                             ordering of seq_cst
                                                             and with equal or
                                                             wider sync scope.
                                                             (Note that seq_cst
                                                             fences have their
                                                             own s_waitcnt
                                                             lgkmcnt(0) and so do
                                                             not need to be
                                                             considered.)
                                                           - Ensures any
                                                             preceding
                                                             sequential
                                                             consistent local
                                                             memory instructions
                                                             have completed
                                                             before executing
                                                             this sequentially
                                                             consistent
                                                             instruction. This
                                                             prevents reordering
                                                             a seq_cst store
                                                             followed by a
                                                             seq_cst load. (Note
                                                             that seq_cst is
                                                             stronger than
                                                             acquire/release as
                                                             the reordering of
                                                             load acquire
                                                             followed by a store
                                                             release is
                                                             prevented by the
                                                             waitcnt of
                                                             the release, but
                                                             there is nothing
                                                             preventing a store
                                                             release followed by
                                                             load acquire from
                                                             competing out of
                                                             order.)

                                                         2. *Following
                                                            instructions same as
                                                            corresponding load
                                                            atomic acquire,
                                                            except must generated
                                                            all instructions even
                                                            for OpenCL.*
     load atomic  seq_cst      - workgroup    - local    *Same as corresponding
                                                         load atomic acquire,
                                                         except must generated
                                                         all instructions even
                                                         for OpenCL.*
     load atomic  seq_cst      - agent        - global   1. s_waitcnt lgkmcnt(0) &
                               - system       - generic     vmcnt(0)

                                                           - Could be split into
                                                             separate s_waitcnt
                                                             vmcnt(0)
                                                             and s_waitcnt
                                                             lgkmcnt(0) to allow
                                                             them to be
                                                             independently moved
                                                             according to the
                                                             following rules.
                                                           - waitcnt lgkmcnt(0)
                                                             must happen after
                                                             preceding
                                                             global/generic load
                                                             atomic/store
                                                             atomic/atomicrmw
                                                             with memory
                                                             ordering of seq_cst
                                                             and with equal or
                                                             wider sync scope.
                                                             (Note that seq_cst
                                                             fences have their
                                                             own s_waitcnt
                                                             lgkmcnt(0) and so do
                                                             not need to be
                                                             considered.)
                                                           - waitcnt vmcnt(0)
                                                             must happen after
                                                             preceding
                                                             global/generic load
                                                             atomic/store
                                                             atomic/atomicrmw
                                                             with memory
                                                             ordering of seq_cst
                                                             and with equal or
                                                             wider sync scope.
                                                             (Note that seq_cst
                                                             fences have their
                                                             own s_waitcnt
                                                             vmcnt(0) and so do
                                                             not need to be
                                                             considered.)
                                                           - Ensures any
                                                             preceding
                                                             sequential
                                                             consistent global
                                                             memory instructions
                                                             have completed
                                                             before executing
                                                             this sequentially
                                                             consistent
                                                             instruction. This
                                                             prevents reordering
                                                             a seq_cst store
                                                             followed by a
                                                             seq_cst load. (Note
                                                             that seq_cst is
                                                             stronger than
                                                             acquire/release as
                                                             the reordering of
                                                             load acquire
                                                             followed by a store
                                                             release is
                                                             prevented by the
                                                             waitcnt of
                                                             the release, but
                                                             there is nothing
                                                             preventing a store
                                                             release followed by
                                                             load acquire from
                                                             competing out of
                                                             order.)

                                                         2. *Following
                                                            instructions same as
                                                            corresponding load
                                                            atomic acquire,
                                                            except must generated
                                                            all instructions even
                                                            for OpenCL.*
     store atomic seq_cst      - singlethread - global   *Same as corresponding
                               - wavefront    - local    store atomic release,
                               - workgroup    - generic  except must generated
                                                         all instructions even
                                                         for OpenCL.*
     store atomic seq_cst      - agent        - global   *Same as corresponding
                               - system       - generic  store atomic release,
                                                         except must generated
                                                         all instructions even
                                                         for OpenCL.*
     atomicrmw    seq_cst      - singlethread - global   *Same as corresponding
                               - wavefront    - local    atomicrmw acq_rel,
                               - workgroup    - generic  except must generated
                                                         all instructions even
                                                         for OpenCL.*
     atomicrmw    seq_cst      - agent        - global   *Same as corresponding
                               - system       - generic  atomicrmw acq_rel,
                                                         except must generated
                                                         all instructions even
                                                         for OpenCL.*
     fence        seq_cst      - singlethread *none*     *Same as corresponding
                               - wavefront               fence acq_rel,
                               - workgroup               except must generated
                               - agent                   all instructions even
                               - system                  for OpenCL.*
     ============ ============ ============== ========== ===============================

The memory order also adds the single thread optimization constrains defined in
table
:ref:`amdgpu-amdhsa-memory-model-single-thread-optimization-constraints-gfx6-gfx9-table`.

  .. table:: AMDHSA Memory Model Single Thread Optimization Constraints GFX6-GFX9
     :name: amdgpu-amdhsa-memory-model-single-thread-optimization-constraints-gfx6-gfx9-table

     ============ ==============================================================
     LLVM Memory  Optimization Constraints
     Ordering
     ============ ==============================================================
     unordered    *none*
     monotonic    *none*
     acquire      - If a load atomic/atomicrmw then no following load/load
                    atomic/store/ store atomic/atomicrmw/fence instruction can
                    be moved before the acquire.
                  - If a fence then same as load atomic, plus no preceding
                    associated fence-paired-atomic can be moved after the fence.
     release      - If a store atomic/atomicrmw then no preceding load/load
                    atomic/store/ store atomic/atomicrmw/fence instruction can
                    be moved after the release.
                  - If a fence then same as store atomic, plus no following
                    associated fence-paired-atomic can be moved before the
                    fence.
     acq_rel      Same constraints as both acquire and release.
     seq_cst      - If a load atomic then same constraints as acquire, plus no
                    preceding sequentially consistent load atomic/store
                    atomic/atomicrmw/fence instruction can be moved after the
                    seq_cst.
                  - If a store atomic then the same constraints as release, plus
                    no following sequentially consistent load atomic/store
                    atomic/atomicrmw/fence instruction can be moved before the
                    seq_cst.
                  - If an atomicrmw/fence then same constraints as acq_rel.
     ============ ==============================================================

Trap Handler ABI
~~~~~~~~~~~~~~~~

For code objects generated by AMDGPU backend for HSA [HSA]_ compatible runtimes
(such as ROCm [AMD-ROCm]_), the runtime installs a trap handler that supports
the ``s_trap`` instruction with the following usage:

  .. table:: AMDGPU Trap Handler for AMDHSA OS
     :name: amdgpu-trap-handler-for-amdhsa-os-table

     =================== =============== =============== =======================
     Usage               Code Sequence   Trap Handler    Description
                                         Inputs
     =================== =============== =============== =======================
     reserved            ``s_trap 0x00``                 Reserved by hardware.
     ``debugtrap(arg)``  ``s_trap 0x01`` ``SGPR0-1``:    Reserved for HSA
                                           ``queue_ptr`` ``debugtrap``
                                         ``VGPR0``:      intrinsic (not
                                           ``arg``       implemented).
     ``llvm.trap``       ``s_trap 0x02`` ``SGPR0-1``:    Causes dispatch to be
                                           ``queue_ptr`` terminated and its
                                                         associated queue put
                                                         into the error state.
     ``llvm.debugtrap``  ``s_trap 0x03`` ``SGPR0-1``:    If debugger not
                                           ``queue_ptr`` installed handled
                                                         same as ``llvm.trap``.
     debugger breakpoint ``s_trap 0x07``                 Reserved for  debugger
                                                         breakpoints.
     debugger            ``s_trap 0x08``                 Reserved for debugger.
     debugger            ``s_trap 0xfe``                 Reserved for debugger.
     debugger            ``s_trap 0xff``                 Reserved for debugger.
     =================== =============== =============== =======================

Unspecified OS
--------------

This section provides code conventions used when the target triple OS is
empty (see :ref:`amdgpu-target-triples`).

Trap Handler ABI
~~~~~~~~~~~~~~~~

For code objects generated by AMDGPU backend for non-amdhsa OS, the runtime does
not install a trap handler. The ``llvm.trap`` and ``llvm.debugtrap``
instructions are handled as follows:

  .. table:: AMDGPU Trap Handler for Non-AMDHSA OS
     :name: amdgpu-trap-handler-for-non-amdhsa-os-table

     =============== =============== ===========================================
     Usage           Code Sequence   Description
     =============== =============== ===========================================
     llvm.trap       s_endpgm        Causes wavefront to be terminated.
     llvm.debugtrap  *none*          Compiler warning given that there is no
                                     trap handler installed.
     =============== =============== ===========================================

Source Languages
================

.. _amdgpu-opencl:

OpenCL
------

When generating code for the OpenCL language the target triple environment
should be ``opencl`` or ``amdgizcl`` (see :ref:`amdgpu-target-triples`).

When the language is OpenCL the following differences occur:

1. The OpenCL memory model is used (see :ref:`amdgpu-amdhsa-memory-model`).
2. The AMDGPU backend adds additional arguments to the kernel.
3. Additional metadata is generated
   (:ref:`amdgpu-amdhsa-hsa-code-object-metadata`).

.. TODO
   Specify what affect this has. Hidden arguments added. Additional metadata
   generated.

.. _amdgpu-hcc:

HCC
---

When generating code for the OpenCL language the target triple environment
should be ``hcc`` (see :ref:`amdgpu-target-triples`).

When the language is OpenCL the following differences occur:

1. The HSA memory model is used (see :ref:`amdgpu-amdhsa-memory-model`).

.. TODO
   Specify what affect this has.

Assembler
---------

AMDGPU backend has LLVM-MC based assembler which is currently in development.
It supports AMDGCN GFX6-GFX9.

This section describes general syntax for instructions and operands. For more
information about instructions, their semantics and supported combinations of
operands, refer to one of instruction set architecture manuals
[AMD-GCN-GFX6]_, [AMD-GCN-GFX7]_, [AMD-GCN-GFX8]_ and [AMD-GCN-GFX9]_.

An instruction has the following syntax (register operands are normally
comma-separated while extra operands are space-separated):

*<opcode> <register_operand0>, ... <extra_operand0> ...*

Operands
~~~~~~~~

The following syntax for register operands is supported:

* SGPR registers: s0, ... or s[0], ...
* VGPR registers: v0, ... or v[0], ...
* TTMP registers: ttmp0, ... or ttmp[0], ...
* Special registers: exec (exec_lo, exec_hi), vcc (vcc_lo, vcc_hi), flat_scratch (flat_scratch_lo, flat_scratch_hi)
* Special trap registers: tba (tba_lo, tba_hi), tma (tma_lo, tma_hi)
* Register pairs, quads, etc: s[2:3], v[10:11], ttmp[5:6], s[4:7], v[12:15], ttmp[4:7], s[8:15], ...
* Register lists: [s0, s1], [ttmp0, ttmp1, ttmp2, ttmp3]
* Register index expressions: v[2*2], s[1-1:2-1]
* 'off' indicates that an operand is not enabled

The following extra operands are supported:

* offset, offset0, offset1
* idxen, offen bits
* glc, slc, tfe bits
* waitcnt: integer or combination of counter values
* VOP3 modifiers:

  - abs (\| \|), neg (\-)

* DPP modifiers:

  - row_shl, row_shr, row_ror, row_rol
  - row_mirror, row_half_mirror, row_bcast
  - wave_shl, wave_shr, wave_ror, wave_rol, quad_perm
  - row_mask, bank_mask, bound_ctrl

* SDWA modifiers:

  - dst_sel, src0_sel, src1_sel (BYTE_N, WORD_M, DWORD)
  - dst_unused (UNUSED_PAD, UNUSED_SEXT, UNUSED_PRESERVE)
  - abs, neg, sext

Instruction Examples
~~~~~~~~~~~~~~~~~~~~

DS
~~

.. code-block:: nasm

  ds_add_u32 v2, v4 offset:16
  ds_write_src2_b64 v2 offset0:4 offset1:8
  ds_cmpst_f32 v2, v4, v6
  ds_min_rtn_f64 v[8:9], v2, v[4:5]


For full list of supported instructions, refer to "LDS/GDS instructions" in ISA Manual.

FLAT
++++

.. code-block:: nasm

  flat_load_dword v1, v[3:4]
  flat_store_dwordx3 v[3:4], v[5:7]
  flat_atomic_swap v1, v[3:4], v5 glc
  flat_atomic_cmpswap v1, v[3:4], v[5:6] glc slc
  flat_atomic_fmax_x2 v[1:2], v[3:4], v[5:6] glc

For full list of supported instructions, refer to "FLAT instructions" in ISA Manual.

MUBUF
+++++

.. code-block:: nasm

  buffer_load_dword v1, off, s[4:7], s1
  buffer_store_dwordx4 v[1:4], v2, ttmp[4:7], s1 offen offset:4 glc tfe
  buffer_store_format_xy v[1:2], off, s[4:7], s1
  buffer_wbinvl1
  buffer_atomic_inc v1, v2, s[8:11], s4 idxen offset:4 slc

For full list of supported instructions, refer to "MUBUF Instructions" in ISA Manual.

SMRD/SMEM
+++++++++

.. code-block:: nasm

  s_load_dword s1, s[2:3], 0xfc
  s_load_dwordx8 s[8:15], s[2:3], s4
  s_load_dwordx16 s[88:103], s[2:3], s4
  s_dcache_inv_vol
  s_memtime s[4:5]

For full list of supported instructions, refer to "Scalar Memory Operations" in ISA Manual.

SOP1
++++

.. code-block:: nasm

  s_mov_b32 s1, s2
  s_mov_b64 s[0:1], 0x80000000
  s_cmov_b32 s1, 200
  s_wqm_b64 s[2:3], s[4:5]
  s_bcnt0_i32_b64 s1, s[2:3]
  s_swappc_b64 s[2:3], s[4:5]
  s_cbranch_join s[4:5]

For full list of supported instructions, refer to "SOP1 Instructions" in ISA Manual.

SOP2
++++

.. code-block:: nasm

  s_add_u32 s1, s2, s3
  s_and_b64 s[2:3], s[4:5], s[6:7]
  s_cselect_b32 s1, s2, s3
  s_andn2_b32 s2, s4, s6
  s_lshr_b64 s[2:3], s[4:5], s6
  s_ashr_i32 s2, s4, s6
  s_bfm_b64 s[2:3], s4, s6
  s_bfe_i64 s[2:3], s[4:5], s6
  s_cbranch_g_fork s[4:5], s[6:7]

For full list of supported instructions, refer to "SOP2 Instructions" in ISA Manual.

SOPC
++++

.. code-block:: nasm

  s_cmp_eq_i32 s1, s2
  s_bitcmp1_b32 s1, s2
  s_bitcmp0_b64 s[2:3], s4
  s_setvskip s3, s5

For full list of supported instructions, refer to "SOPC Instructions" in ISA Manual.

SOPP
++++

.. code-block:: nasm

  s_barrier
  s_nop 2
  s_endpgm
  s_waitcnt 0 ; Wait for all counters to be 0
  s_waitcnt vmcnt(0) & expcnt(0) & lgkmcnt(0) ; Equivalent to above
  s_waitcnt vmcnt(1) ; Wait for vmcnt counter to be 1.
  s_sethalt 9
  s_sleep 10
  s_sendmsg 0x1
  s_sendmsg sendmsg(MSG_INTERRUPT)
  s_trap 1

For full list of supported instructions, refer to "SOPP Instructions" in ISA Manual.

Unless otherwise mentioned, little verification is performed on the operands
of SOPP Instructions, so it is up to the programmer to be familiar with the
range or acceptable values.

VALU
++++

For vector ALU instruction opcodes (VOP1, VOP2, VOP3, VOPC, VOP_DPP, VOP_SDWA),
the assembler will automatically use optimal encoding based on its operands.
To force specific encoding, one can add a suffix to the opcode of the instruction:

* _e32 for 32-bit VOP1/VOP2/VOPC
* _e64 for 64-bit VOP3
* _dpp for VOP_DPP
* _sdwa for VOP_SDWA

VOP1/VOP2/VOP3/VOPC examples:

.. code-block:: nasm

  v_mov_b32 v1, v2
  v_mov_b32_e32 v1, v2
  v_nop
  v_cvt_f64_i32_e32 v[1:2], v2
  v_floor_f32_e32 v1, v2
  v_bfrev_b32_e32 v1, v2
  v_add_f32_e32 v1, v2, v3
  v_mul_i32_i24_e64 v1, v2, 3
  v_mul_i32_i24_e32 v1, -3, v3
  v_mul_i32_i24_e32 v1, -100, v3
  v_addc_u32 v1, s[0:1], v2, v3, s[2:3]
  v_max_f16_e32 v1, v2, v3

VOP_DPP examples:

.. code-block:: nasm

  v_mov_b32 v0, v0 quad_perm:[0,2,1,1]
  v_sin_f32 v0, v0 row_shl:1 row_mask:0xa bank_mask:0x1 bound_ctrl:0
  v_mov_b32 v0, v0 wave_shl:1
  v_mov_b32 v0, v0 row_mirror
  v_mov_b32 v0, v0 row_bcast:31
  v_mov_b32 v0, v0 quad_perm:[1,3,0,1] row_mask:0xa bank_mask:0x1 bound_ctrl:0
  v_add_f32 v0, v0, |v0| row_shl:1 row_mask:0xa bank_mask:0x1 bound_ctrl:0
  v_max_f16 v1, v2, v3 row_shl:1 row_mask:0xa bank_mask:0x1 bound_ctrl:0

VOP_SDWA examples:

.. code-block:: nasm

  v_mov_b32 v1, v2 dst_sel:BYTE_0 dst_unused:UNUSED_PRESERVE src0_sel:DWORD
  v_min_u32 v200, v200, v1 dst_sel:WORD_1 dst_unused:UNUSED_PAD src0_sel:BYTE_1 src1_sel:DWORD
  v_sin_f32 v0, v0 dst_unused:UNUSED_PAD src0_sel:WORD_1
  v_fract_f32 v0, |v0| dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_1
  v_cmpx_le_u32 vcc, v1, v2 src0_sel:BYTE_2 src1_sel:WORD_0

For full list of supported instructions, refer to "Vector ALU instructions".

HSA Code Object Directives
~~~~~~~~~~~~~~~~~~~~~~~~~~

AMDGPU ABI defines auxiliary data in output code object. In assembly source,
one can specify them with assembler directives.

.hsa_code_object_version major, minor
+++++++++++++++++++++++++++++++++++++

*major* and *minor* are integers that specify the version of the HSA code
object that will be generated by the assembler.

.hsa_code_object_isa [major, minor, stepping, vendor, arch]
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


*major*, *minor*, and *stepping* are all integers that describe the instruction
set architecture (ISA) version of the assembly program.

*vendor* and *arch* are quoted strings.  *vendor* should always be equal to
"AMD" and *arch* should always be equal to "AMDGPU".

By default, the assembler will derive the ISA version, *vendor*, and *arch*
from the value of the -mcpu option that is passed to the assembler.

.amdgpu_hsa_kernel (name)
+++++++++++++++++++++++++

This directives specifies that the symbol with given name is a kernel entry point
(label) and the object should contain corresponding symbol of type STT_AMDGPU_HSA_KERNEL.

.amd_kernel_code_t
++++++++++++++++++

This directive marks the beginning of a list of key / value pairs that are used
to specify the amd_kernel_code_t object that will be emitted by the assembler.
The list must be terminated by the *.end_amd_kernel_code_t* directive.  For
any amd_kernel_code_t values that are unspecified a default value will be
used.  The default value for all keys is 0, with the following exceptions:

- *kernel_code_version_major* defaults to 1.
- *machine_kind* defaults to 1.
- *machine_version_major*, *machine_version_minor*, and
  *machine_version_stepping* are derived from the value of the -mcpu option
  that is passed to the assembler.
- *kernel_code_entry_byte_offset* defaults to 256.
- *wavefront_size* defaults to 6.
- *kernarg_segment_alignment*, *group_segment_alignment*, and
  *private_segment_alignment* default to 4. Note that alignments are specified
  as a power of two, so a value of **n** means an alignment of 2^ **n**.

The *.amd_kernel_code_t* directive must be placed immediately after the
function label and before any instructions.

For a full list of amd_kernel_code_t keys, refer to AMDGPU ABI document,
comments in lib/Target/AMDGPU/AmdKernelCodeT.h and test/CodeGen/AMDGPU/hsa.s.

Here is an example of a minimal amd_kernel_code_t specification:

.. code-block:: none

   .hsa_code_object_version 1,0
   .hsa_code_object_isa

   .hsatext
   .globl  hello_world
   .p2align 8
   .amdgpu_hsa_kernel hello_world

   hello_world:

      .amd_kernel_code_t
         enable_sgpr_kernarg_segment_ptr = 1
         is_ptr64 = 1
         compute_pgm_rsrc1_vgprs = 0
         compute_pgm_rsrc1_sgprs = 0
         compute_pgm_rsrc2_user_sgpr = 2
         kernarg_segment_byte_size = 8
         wavefront_sgpr_count = 2
         workitem_vgpr_count = 3
     .end_amd_kernel_code_t

     s_load_dwordx2 s[0:1], s[0:1] 0x0
     v_mov_b32 v0, 3.14159
     s_waitcnt lgkmcnt(0)
     v_mov_b32 v1, s0
     v_mov_b32 v2, s1
     flat_store_dword v[1:2], v0
     s_endpgm
   .Lfunc_end0:
        .size   hello_world, .Lfunc_end0-hello_world

Additional Documentation
========================

.. [AMD-RADEON-HD-2000-3000] `AMD R6xx shader ISA <http://developer.amd.com/wordpress/media/2012/10/R600_Instruction_Set_Architecture.pdf>`__
.. [AMD-RADEON-HD-4000] `AMD R7xx shader ISA <http://developer.amd.com/wordpress/media/2012/10/R700-Family_Instruction_Set_Architecture.pdf>`__
.. [AMD-RADEON-HD-5000] `AMD Evergreen shader ISA <http://developer.amd.com/wordpress/media/2012/10/AMD_Evergreen-Family_Instruction_Set_Architecture.pdf>`__
.. [AMD-RADEON-HD-6000] `AMD Cayman/Trinity shader ISA <http://developer.amd.com/wordpress/media/2012/10/AMD_HD_6900_Series_Instruction_Set_Architecture.pdf>`__
.. [AMD-GCN-GFX6] `AMD Southern Islands Series ISA <http://developer.amd.com/wordpress/media/2012/12/AMD_Southern_Islands_Instruction_Set_Architecture.pdf>`__
.. [AMD-GCN-GFX7] `AMD Sea Islands Series ISA <http://developer.amd.com/wordpress/media/2013/07/AMD_Sea_Islands_Instruction_Set_Architecture.pdf>`_
.. [AMD-GCN-GFX8] `AMD GCN3 Instruction Set Architecture <http://amd-dev.wpengine.netdna-cdn.com/wordpress/media/2013/12/AMD_GCN3_Instruction_Set_Architecture_rev1.1.pdf>`__
.. [AMD-GCN-GFX9] `AMD "Vega" Instruction Set Architecture <http://developer.amd.com/wordpress/media/2013/12/Vega_Shader_ISA_28July2017.pdf>`__
.. [AMD-ROCm] `ROCm: Open Platform for Development, Discovery and Education Around GPU Computing <http://gpuopen.com/compute-product/rocm/>`__
.. [AMD-ROCm-github] `ROCm github <http://github.com/RadeonOpenCompute>`__
.. [HSA] `Heterogeneous System Architecture (HSA) Foundation <http://www.hsafoundation.com/>`__
.. [ELF] `Executable and Linkable Format (ELF) <http://www.sco.com/developers/gabi/>`__
.. [DWARF] `DWARF Debugging Information Format <http://dwarfstd.org/>`__
.. [YAML] `YAML Ain't Markup Language (YAML™) Version 1.2 <http://www.yaml.org/spec/1.2/spec.html>`__
.. [OpenCL] `The OpenCL Specification Version 2.0 <http://www.khronos.org/registry/cl/specs/opencl-2.0.pdf>`__
.. [HRF] `Heterogeneous-race-free Memory Models <http://benedictgaster.org/wp-content/uploads/2014/01/asplos269-FINAL.pdf>`__