[PATCH] D59744: Fix i386 ABI "__m64" type bug

[Eli Friedman via Phabricator via cfe-commits]

efriedma added a comment.

> Now, we could theoretically use a different ABI rule for vectors defined with Clang-specific extensions, but that seems like it would cause quite a few problems of its own.

I think we can't reasonably impose this ABI rule on vectors defined with ext_vector_type: that makes it impossible to build portable OpenCL code for 32-bit x86, given the side-effects of introducing any use of the x86_mmx type.  So that leaves us with two options: make vector_size and ext_vector_type incompatible, or revert this patch and intentionally remain ABI-incompatible with gcc. (I guess we could theoretically try to separate out a special case for OpenCL instead, but that seems even more fragile.)

Being ABI-incompatible is obviously inconvenient if you're writing code using MMX types/intrinsics, but using MMX intrinsics is sort of "at your own risk" anyway, given neither LLVM nor gcc properly manages the state of the MMX/x87 register file.


Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D59744/new/

https://reviews.llvm.org/D59744