CodeGen: Allow virtual registers in bundles
The note in the documentation suggests this restriction is a compile
time optimization for architectures that make heavy use of
bundling. Allowing virtual registers in a bundle is useful for some
(non-R600) AMDGPU use cases and are infrequent enough to matter.
A more common AMDGPU use case has already been using virtual registers
in bundles since r333691, although never calling finalizeBundle on
them and manually creating the use/def list on the BUNDLE
instruction. This is also relatively infrequent, and only happens for
consecutive sequences of some load/store types.
llvm-svn: 367597
diff --git a/llvm/docs/CodeGenerator.rst b/llvm/docs/CodeGenerator.rst
index 75d893b..343b987 100644
--- a/llvm/docs/CodeGenerator.rst
+++ b/llvm/docs/CodeGenerator.rst
@@ -579,15 +579,18 @@
register MachineOperand's that represent the cumulative inputs and outputs of
the bundled MIs.
-Packing / bundling of MachineInstr's should be done as part of the register
-allocation super-pass. More specifically, the pass which determines what MIs
-should be bundled together must be done after code generator exits SSA form
-(i.e. after two-address pass, PHI elimination, and copy coalescing). Bundles
-should only be finalized (i.e. adding BUNDLE MIs and input and output register
-MachineOperands) after virtual registers have been rewritten into physical
-registers. This requirement eliminates the need to add virtual register operands
-to BUNDLE instructions which would effectively double the virtual register def
-and use lists.
+Packing / bundling of MachineInstrs for VLIW architectures should
+generally be done as part of the register allocation super-pass. More
+specifically, the pass which determines what MIs should be bundled
+together should be done after code generator exits SSA form
+(i.e. after two-address pass, PHI elimination, and copy coalescing).
+Such bundles should be finalized (i.e. adding BUNDLE MIs and input and
+output register MachineOperands) after virtual registers have been
+rewritten into physical registers. This eliminates the need to add
+virtual register operands to BUNDLE instructions which would
+effectively double the virtual register def and use lists. Bundles may
+use virtual registers and be formed in SSA form, but may not be
+appropriate for all use cases.
.. _MC Layer: