[InstCombine] Preserve 'exact' in -(X >>u 31) -> (X >>s 31) fold

https://rise4fun.com/Alive/yR4

llvm-svn: 373363

1 files changed, 6 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 9d640e849dc..7e3d405e906 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1676,12 +1676,16 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
       if (match(Op1, m_LShr(m_Value(X), m_APInt(ShAmt))) &&
           *ShAmt == BitWidth - 1) {
         Value *ShAmtOp = cast<Instruction>(Op1)->getOperand(1);
-        return BinaryOperator::CreateAShr(X, ShAmtOp);
+        Instruction *NewShift = BinaryOperator::CreateAShr(X, ShAmtOp);
+        NewShift->copyIRFlags(Op1);
+        return NewShift;
       }
       if (match(Op1, m_AShr(m_Value(X), m_APInt(ShAmt))) &&
           *ShAmt == BitWidth - 1) {
         Value *ShAmtOp = cast<Instruction>(Op1)->getOperand(1);
-        return BinaryOperator::CreateLShr(X, ShAmtOp);
+        Instruction *NewShift = BinaryOperator::CreateLShr(X, ShAmtOp);
+        NewShift->copyIRFlags(Op1);
+        return NewShift;
       }
 
       if (Op1->hasOneUse()) {