[llvm] 7b8d50b - [InstSimplify] Clarify use of FixedVectorType in SimplifySelectInst

[Cullen Rhodes via llvm-commits]

Author: Cullen Rhodes
Date: 2020-11-27T09:55:29Z
New Revision: 7b8d50b141bbf223eab33a75f468be4ee92ad052

URL: https://github.com/llvm/llvm-project/commit/7b8d50b141bbf223eab33a75f468be4ee92ad052
DIFF: https://github.com/llvm/llvm-project/commit/7b8d50b141bbf223eab33a75f468be4ee92ad052.diff

LOG: [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

Added: 
    

Modified: 
    llvm/lib/Analysis/InstructionSimplify.cpp
    llvm/test/Transforms/InstSimplify/select.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 813fb6c89863..6b116eb0ed00 100644
--- 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 2dcd29753788..4cbc5832d234 100644
--- 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
+}