1 files changed, 8 insertions, 2 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
index a87e323fd4b..c391034dc00 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -918,6 +918,13 @@ static bool canEvaluateShuffled(Value *V, ArrayRef<int> Mask,
     case Instruction::FPTrunc:
     case Instruction::FPExt:
     case Instruction::GetElementPtr: {
+      // Bail out if we would create longer vector ops. We could allow creating
+      // longer vector ops, but that may result in more expensive codegen. We
+      // would also need to limit the transform to avoid undefined behavior for
+      // integer div/rem.
+      Type *ITy = I->getType();
+      if (ITy->isVectorTy() && Mask.size() > ITy->getVectorNumElements())
+        return false;
       for (Value *Operand : I->operands()) {
         if (!canEvaluateShuffled(Operand, Mask, Depth - 1))
           return false;
@@ -1464,8 +1471,7 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
     if (isRHSID) return replaceInstUsesWith(SVI, RHS);
   }
 
-  if (isa<UndefValue>(RHS) && !SVI.increasesLength() &&
-      canEvaluateShuffled(LHS, Mask)) {
+  if (isa<UndefValue>(RHS) && canEvaluateShuffled(LHS, Mask)) {
     Value *V = evaluateInDifferentElementOrder(LHS, Mask);
     return replaceInstUsesWith(SVI, V);
   }