[PATCH] D28119: [InstCombine][X86] Add DemandedElts support for PMULDQ/PMULUDQ instructions

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: craig.topper, m_zuckerman, andreadb, spatel.
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PMULDQ/PMULUDQ vXi64 instructions only use the even numbered v2Xi32 input elements which SimplifyDemandedVectorElts should try and use.

We can't do much with the undef demanded elts - we should probably only support the (mul X, undef -> 0) pattern the same as regular integer multiplies. I can add support for it if you guys want but I can't see it being used by real world code. Same with constant folding support.


Repository:
  rL LLVM

https://reviews.llvm.org/D28119

Files:
  lib/Transforms/InstCombine/InstCombineCalls.cpp
  lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
  test/Transforms/InstCombine/x86-muldq.ll

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