[InstCombine] Fix poison safety of folding shufflevector into select #115483
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@llvm/pr-subscribers-llvm-transforms Author: Yingwei Zheng (dtcxzyw) ChangesWe are allowed to fold shufflevector into select iff the condition is guaranteed not to be poison or the RHS is a poison. Closes #115465. Full diff: https://github.com/llvm/llvm-project/pull/115483.diff 2 Files Affected:
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
index 454fe5a91d375a..ede89b099e8deb 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -2904,7 +2904,9 @@ Instruction *InstCombinerImpl::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
if (auto *SI = dyn_cast<SelectInst>(LHS)) {
// We cannot do this fold for elementwise select since ShuffleVector is
// not elementwise.
- if (SI->getCondition()->getType()->isIntegerTy()) {
+ if (SI->getCondition()->getType()->isIntegerTy() &&
+ (isa<PoisonValue>(RHS) ||
+ isGuaranteedNotToBePoison(SI->getCondition()))) {
if (Instruction *I = FoldOpIntoSelect(SVI, SI))
return I;
}
diff --git a/llvm/test/Transforms/InstCombine/vec_shuffle.ll b/llvm/test/Transforms/InstCombine/vec_shuffle.ll
index 163d9c9557b239..9fb68b5399c845 100644
--- a/llvm/test/Transforms/InstCombine/vec_shuffle.ll
+++ b/llvm/test/Transforms/InstCombine/vec_shuffle.ll
@@ -2411,6 +2411,18 @@ define <4 x i32> @shuf_same_length_vec_select(<4 x i1> %cond) {
ret <4 x i32> %shuf
}
+; Make sure we do not fold in this case.
+define <4 x i8> @shuf_cmp_may_be_poison(<4 x i8> %x, <4 x i8> %y, i1 %cmp) {
+; CHECK-LABEL: @shuf_cmp_may_be_poison(
+; CHECK-NEXT: [[Y:%.*]] = select i1 [[CMP:%.*]], <4 x i8> [[Y1:%.*]], <4 x i8> <i8 0, i8 poison, i8 0, i8 poison>
+; CHECK-NEXT: [[TMP1:%.*]] = shufflevector <4 x i8> [[Y]], <4 x i8> <i8 poison, i8 1, i8 poison, i8 3>, <4 x i32> <i32 0, i32 5, i32 2, i32 7>
+; CHECK-NEXT: ret <4 x i8> [[TMP1]]
+;
+ %sel = select i1 %cmp, <4 x i8> %y, <4 x i8> <i8 0, i8 poison, i8 0, i8 poison>
+ %shuf = shufflevector <4 x i8> %sel, <4 x i8> <i8 poison, i8 1, i8 poison, i8 3>, <4 x i32> <i32 0, i32 5, i32 2, i32 7>
+ ret <4 x i8> %shuf
+}
+
declare i1 @cond()
declare <4 x i32> @value()
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…lvm#115483) We are allowed to fold shufflevector into select iff the condition is guaranteed not to be poison or the RHS is a poison. Alive2: https://alive2.llvm.org/ce/z/28zEWR Closes llvm#115465.
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We are allowed to fold shufflevector into select iff the condition is guaranteed not to be poison or the RHS is a poison.
Alive2: https://alive2.llvm.org/ce/z/28zEWR
Closes #115465.