[CXX TLS calling convention] Add CXX TLS calling convention.
This commit adds a new target-independent calling convention for C++ TLS
access functions. It aims to minimize overhead in the caller by perserving as
many registers as possible.
The target-specific implementation for X86-64 is defined as following:
Arguments are passed as for the default C calling convention
The same applies for the return value(s)
The callee preserves all GPRs - except RAX and RDI
The access function makes C-style TLS function calls in the entry and exit
block, C-style TLS functions save a lot more registers than normal calls.
The added calling convention ties into the existing implementation of the
C-style TLS functions, so we can't simply use existing calling conventions
such as preserve_mostcc.
rdar://9001553
llvm-svn: 254737
diff --git a/llvm/docs/BitCodeFormat.rst b/llvm/docs/BitCodeFormat.rst
index 62d66f8..d6e3099 100644
--- a/llvm/docs/BitCodeFormat.rst
+++ b/llvm/docs/BitCodeFormat.rst
@@ -756,6 +756,7 @@
* ``anyregcc``: code 13
* ``preserve_mostcc``: code 14
* ``preserve_allcc``: code 15
+ * ``cxx_fast_tlscc``: code 17
* ``x86_stdcallcc``: code 64
* ``x86_fastcallcc``: code 65
* ``arm_apcscc``: code 66