SimplifyInstruction does not imply DCE

We cannot remove an instruction with no uses just because
SimplifyInstruction succeeds.  It may have side effects.

llvm-svn: 273711

1 files changed, 7 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
index 1d8d2a5e469..e7957f9599a 100644
--- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -1746,13 +1746,18 @@ bool JumpThreadingPass::DuplicateCondBranchOnPHIIntoPred(
     // phi translation.
     if (Value *IV =
             SimplifyInstruction(New, BB->getModule()->getDataLayout())) {
-      delete New;
       ValueMapping[&*BI] = IV;
+      if (!New->mayHaveSideEffects()) {
+        delete New;
+        New = nullptr;
+      }
     } else {
+      ValueMapping[&*BI] = New;
+    }
+    if (New) {
       // Otherwise, insert the new instruction into the block.
       New->setName(BI->getName());
       PredBB->getInstList().insert(OldPredBranch->getIterator(), New);
-      ValueMapping[&*BI] = New;
     }
   }