[PATCH] D155295: [InstCombine] Allow SimplifyDemandedVectorElts to look through freeze

[Nuno Lopes via Phabricator via llvm-commits]

nlopes added inline comments.


================
Comment at: llvm/test/Transforms/InstCombine/shufflevector_freezepoison.ll:17
 ; CHECK-LABEL: @shuffle_op1_freeze_poison(
-; CHECK-NEXT:    [[B:%.*]] = freeze <2 x double> poison
-; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <2 x double> [[A:%.*]], <2 x double> [[B]], <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <2 x double> [[A:%.*]], <2 x double> undef, <4 x i32> <i32 0, i32 1, i32 poison, i32 poison>
 ; CHECK-NEXT:    ret <4 x double> [[SHUFFLE]]
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this transformation isn't correct.
It replaces <a[0], a[1], freeze poison, freeze poison>
with: <a[0], a[1], poison, poison>.

OOB or poison indexes in the mask yield a poison element.

Not sure if the bug is in this patch or if it was already there though. The code needs probably needs to separate undef from poison elements.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D155295/new/

https://reviews.llvm.org/D155295