[PATCH] D44997: [InstCombine] Fold compare of int constant against an integer vector splat

[Daniel Neilson via Phabricator via llvm-commits]

dneilson created this revision.
dneilson added reviewers: spatel, anna, mkazantsev.
Herald added a subscriber: rengolin.

Folding patterns like:

  %insvec = insertelement <4 x i8> undef, i8 %val, i32 0
  %vec = shufflevector <4 x i8> %insvec, <4 x i8> undef, <4 x i32> zeroinitializer
  %cast = bitcast <4 x i8> %vec to i32
  %cond = icmp eq i32 %cast, 0

into:

  %cond = icmp eq i8 %val, 0

When we construct a vector via a splat, and bitcast the vector
into an integer type for comparison against an integer constant. Then
if the compared-to integer constant is a splat of a pattern with the same
bitwidth as the originally splatted integer we can fold the comparison
into a compare between the splatted integer value and constant.


Repository:
  rL LLVM

https://reviews.llvm.org/D44997

Files:
  lib/Transforms/InstCombine/InstCombineCompares.cpp
  lib/Transforms/InstCombine/InstCombineInternal.h
  test/Transforms/InstCombine/icmp-bc-vecsplat.ll

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