LLVM prefers vxorps to vpxor when out-of-context

[gnzlbg]

LLVM prefers to generate vxorps instructions to vpxor when out-of-context even though one might be using integer vectors because the encoding of that instruction is shorter.

There is an LLVM patch for this here: https://reviews.llvm.org/D7401
And a bug report with some more information here:

• https://bugs.llvm.org/show_bug.cgi?id=36127

This affects following intrinsics (maybe incomplete):

• _mm256_xor_si256 (need to add a comment to the source code)