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, 6 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 51c3262..377ccb9 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2830,7 +2830,8 @@ bool InstCombiner::run() {
         // Add operands to the worklist.
         replaceInstUsesWith(*I, C);
         ++NumConstProp;
-        eraseInstFromFunction(*I);
+        if (isInstructionTriviallyDead(I, TLI))
+          eraseInstFromFunction(*I);
         MadeIRChange = true;
         continue;
       }
@@ -2851,7 +2852,8 @@ bool InstCombiner::run() {
         // Add operands to the worklist.
         replaceInstUsesWith(*I, C);
         ++NumConstProp;
-        eraseInstFromFunction(*I);
+        if (isInstructionTriviallyDead(I, TLI))
+          eraseInstFromFunction(*I);
         MadeIRChange = true;
         continue;
       }
@@ -3007,7 +3009,8 @@ static bool AddReachableCodeToWorklist(BasicBlock *BB, const DataLayout &DL,
                        << *Inst << '\n');
           Inst->replaceAllUsesWith(C);
           ++NumConstProp;
-          Inst->eraseFromParent();
+          if (isInstructionTriviallyDead(Inst, TLI))
+            Inst->eraseFromParent();
           continue;
         }