[InstSimplify] Clarify use of FixedVectorType in SimplifySelectInst

Folding a select of vector constants that include undef elements only
applies to fixed vectors, but there's no earlier check the type is not
scalable so it crashes for scalable vectors. This adds a check so this
optimization is only attempted for fixed vectors.

Reviewed By: sdesmalen

Differential Revision: https://reviews.llvm.org/D92046

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 813fb6c..6b116eb 100644 (file)
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4136,7 +4136,8 @@ static Value *SimplifySelectInst(Value *Cond, Value *TrueVal, Value *FalseVal,
 
   // Deal with partial undef vector constants: select ?, VecC, VecC' --> VecC''
   Constant *TrueC, *FalseC;
-  if (TrueVal->getType()->isVectorTy() && match(TrueVal, m_Constant(TrueC)) &&
+  if (isa<FixedVectorType>(TrueVal->getType()) &&
+      match(TrueVal, m_Constant(TrueC)) &&
       match(FalseVal, m_Constant(FalseC))) {
     unsigned NumElts =
         cast<FixedVectorType>(TrueC->getType())->getNumElements();

diff --git a/llvm/test/Transforms/InstSimplify/select.ll b/llvm/test/Transforms/InstSimplify/select.ll
index 2dcd297..4cbc583 100644 (file)
--- a/llvm/test/Transforms/InstSimplify/select.ll
+++ b/llvm/test/Transforms/InstSimplify/select.ll
@@ -957,3 +957,14 @@ define i32 @pr47322_more_poisonous_replacement(i32 %arg) {
   ret i32 %r1.sroa.0.1
 }
 declare i32 @llvm.cttz.i32(i32, i1 immarg)
+
+; Partial undef scalable vectors should be ignored.
+define <vscale x 2 x i1> @ignore_scalable_undef(<vscale x 2 x i1> %cond) {
+; CHECK-LABEL: @ignore_scalable_undef(
+; CHECK-NEXT:    [[S:%.*]] = select <vscale x 2 x i1> [[COND:%.*]], <vscale x 2 x i1> undef, <vscale x 2 x i1> insertelement (<vscale x 2 x i1> undef, i1 true, i32 0)
+; CHECK-NEXT:    ret <vscale x 2 x i1> [[S]]
+;
+  %vec = insertelement <vscale x 2 x i1> undef, i1 true, i32 0
+  %s = select <vscale x 2 x i1> %cond, <vscale x 2 x i1> undef, <vscale x 2 x i1> %vec
+  ret <vscale x 2 x i1> %s
+}