[PATCH] 128-bit ABI for x86_64-w64-mingw32 incorrectly generated

[Jameson Nash]

  > @vtjnash obviously, everything should be moved into X86 target. Any check for "win64" and similar stuff inside the common codegen is not acceptable at all. However, first you need to show that there is indeed a problem somewhere - I believe that the calling convention bits for 128 bit stuff is correct there.

  I understand and agree. However, CodeGen here is implicitly assuming a calling convention for i128 types without acknowledging that it is doing target specific work -- in particular, it assumes that the library intrinsics functions (e.g. __modti3, provided by gcc-4.8) operate on registers, whereas WIN64 i128 uses a different calling convention (passed as pointers but returned in xmm0).

  > It looks like you're trying to match VCPP here, since you're using "-win32" target triple. However, you're calling __modti3 here, which is definitely not provided by VCPP...

  True, I was running the tests on MinGW64 and OSX while I am waiting for the MSVC build to finish. LLVM is creating the call to __modti3, based on the llvm srem intrinsic.

  >Win64 ABI does not define the calling convention for __int128 (see http://msdn.microsoft.com/en-us/library/zthk2dkh.aspx). So, will you please indicate the document describing the desired behavior?

  it does not explicitly call out i128, but it does state that anything over 8 bytes is unconditionally passed as a pointer. also relevant:
  https://groups.google.com/forum/#!topic/llvm-dev/wZg9CnTevFI

http://reviews.llvm.org/D1998