[Reassociate] Don't propogate flags when creating negations

Reassociate mutated existing instructions in order to form negations
which would create additional reassociate opportunities.

This fixes PR23926.

llvm-svn: 240593

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/Reassociate.cpp b/llvm/lib/Transforms/Scalar/Reassociate.cpp
index 6c66b58729e..d1acf785d07 100644
--- a/llvm/lib/Transforms/Scalar/Reassociate.cpp
+++ b/llvm/lib/Transforms/Scalar/Reassociate.cpp
@@ -936,6 +936,10 @@ static Value *NegateValue(Value *V, Instruction *BI) {
     // Push the negates through the add.
     I->setOperand(0, NegateValue(I->getOperand(0), BI));
     I->setOperand(1, NegateValue(I->getOperand(1), BI));
+    if (I->getOpcode() == Instruction::Add) {
+      I->setHasNoUnsignedWrap(false);
+      I->setHasNoSignedWrap(false);
+    }
 
     // We must move the add instruction here, because the neg instructions do
     // not dominate the old add instruction in general.  By moving it, we are
@@ -976,6 +980,12 @@ static Value *NegateValue(Value *V, Instruction *BI) {
       InsertPt = TheNeg->getParent()->getParent()->getEntryBlock().begin();
     }
     TheNeg->moveBefore(InsertPt);
+    if (TheNeg->getOpcode() == Instruction::Sub) {
+      TheNeg->setHasNoUnsignedWrap(false);
+      TheNeg->setHasNoSignedWrap(false);
+    } else {
+      TheNeg->andIRFlags(BI);
+    }
     return TheNeg;
   }