[X86] Add a hack to combinePMULDQ to manually turn...

[X86] Add a hack to combinePMULDQ to manually turn SIGN_EXTEND_VECTOR_INREG/ZERO_EXTEND_VECTOR_INREG inputs into an ANY_EXTEND_VECTOR_INREG style shuffle

ANY_EXTEND_VECTOR_INREG isn't currently marked Legal which prevents SimplifyDemandedBits from turning SIGN/ZERO_EXTEND_VECTOR_INREG into it after op legalization. And even if we did make it Legal, combineExtInVec doesn't do shuffle combining on the VECTOR_INREG nodes until AVX1.

This patch adds a quick hack to combinePMULDQ to directly emit a vector shuffle corresponding to an ANY_EXTEND_VECTOR_INREG operation. This avoids both of those issues without creating any other regressions on our tests. The xop-ifma.ll change here also showed up when I tried to resurrect D56306 and seemed to be the only improvement that patch creates now. This is a more direct way to get the benefit.

Differential Revision: https://reviews.llvm.org/D66436

llvm-svn: 369942