[cfe-commits] [PATCH] Ignored calling conventions

[Aaron Ballman]

MSDN documents that the __stdcall calling convention will be silently
ignored if it is used when compiling for x64
(http://msdn.microsoft.com/en-us/library/zxk0tw93(v=vs.110).aspx).
This patch will mimic that behavior in clang as well by treating the
calling convention as C when generating code as well as when mangling
the convention.  This is important for Win64 support because the Win32
APIs are all prefixed with __stdcall, even when compiling for x64.
Currently, we cannot link against the Win64 APIs because of this
problem.

The approach I am taking is a cautious one, so it only targets x64 in
Microsoft mode for __stdcall.  However, I think it may make sense to
have a more generalized approach to handling calling conventions
because I suspect there will be other cases we wish to do this for
more than just MSVC compatibility.  We cannot simply drop or modify
the attribute on the function because then we would be unable to
perform rewrites from the AST, and we don't want to foist the problem
off on the backend either.  Thoughts are welcome as to a reasonable
approach -- I wasn't able to find a satisfactory way to express the
notion of a written calling convention that doesn't match what we
actually wish to emit.

Thanks!

~Aaron
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