Don't remove side effecting instructions due to ConstantFoldInstruction

Just because we can constant fold the result of an instruction does not
imply that we can delete the instruction.  It may have side effects.

This fixes PR28655.

llvm-svn: 276389

1 files changed, 5 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Scalar/ConstantProp.cpp b/llvm/lib/Transforms/Scalar/ConstantProp.cpp
index 88172d19fe5..9e982194bac 100644
--- a/llvm/lib/Transforms/Scalar/ConstantProp.cpp
+++ b/llvm/lib/Transforms/Scalar/ConstantProp.cpp
@@ -19,6 +19,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/Local.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/IR/Constant.h"
@@ -90,11 +91,13 @@ bool ConstantPropagation::runOnFunction(Function &F) {
 
         // Remove the dead instruction.
         WorkList.erase(I);
-        I->eraseFromParent();
+        if (isInstructionTriviallyDead(I, TLI)) {
+          I->eraseFromParent();
+          ++NumInstKilled;
+        }
 
         // We made a change to the function...
         Changed = true;
-        ++NumInstKilled;
       }
   }
   return Changed;