Fix a bug about generating undef operand when optimising shuffle vector and insert element in instruction combine.

llvm-svn: 198730

1 files changed, 3 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
index 1e724106991..c0b9b2fc3e5 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -763,9 +763,10 @@ InstCombiner::EvaluateInDifferentElementOrder(Value *V, ArrayRef<int> Mask) {
         }
       }
 
+      // If element is not in Mask, no need to handle the operand 1 (element to
+      // be inserted). Just evaluate values in operand 0 according to Mask.
       if (!Found)
-        return UndefValue::get(
-            VectorType::get(V->getType()->getScalarType(), Mask.size()));
+        return EvaluateInDifferentElementOrder(I->getOperand(0), Mask);
 
       Value *V = EvaluateInDifferentElementOrder(I->getOperand(0), Mask);
       return InsertElementInst::Create(V, I->getOperand(1),