[EarlyCSE] Correctly handle simplified, but live, instructions

Some instructions may have their uses replaced with a symbolic constant.
However, the instruction may still have side effects which percludes it
from being removed from the function.  EarlyCSE treated such an
instruction as if it were removed, resulting in PR28763.

llvm-svn: 277114

1 files changed, 4 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
index 9d0ef42e039..0b16e2703dc 100644
--- a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
+++ b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
@@ -582,6 +582,7 @@ bool EarlyCSE::processNode(DomTreeNode *Node) {
     // its simpler value.
     if (Value *V = SimplifyInstruction(Inst, DL, &TLI, &DT, &AC)) {
       DEBUG(dbgs() << "EarlyCSE Simplify: " << *Inst << "  to: " << *V << '\n');
+      bool Killed = false;
       if (!Inst->use_empty()) {
         Inst->replaceAllUsesWith(V);
         Changed = true;
@@ -589,11 +590,12 @@ bool EarlyCSE::processNode(DomTreeNode *Node) {
       if (isInstructionTriviallyDead(Inst, &TLI)) {
         Inst->eraseFromParent();
         Changed = true;
+        Killed = true;
       }
-      if (Changed) {
+      if (Changed)
         ++NumSimplify;
+      if (Killed)
         continue;
-      }
     }
 
     // If this is a simple instruction that we can value number, process it.