[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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@277114 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/EarlyCSE.cpp b/lib/Transforms/Scalar/EarlyCSE.cpp
index 9d0ef42..0b16e27 100644 (file)
--- a/lib/Transforms/Scalar/EarlyCSE.cpp
+++ b/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.

diff --git a/test/Transforms/EarlyCSE/basic.ll b/test/Transforms/EarlyCSE/basic.ll
index fa1a705..3c427d8 100644 (file)
--- a/test/Transforms/EarlyCSE/basic.ll
+++ b/test/Transforms/EarlyCSE/basic.ll
@@ -276,3 +276,17 @@ define void @dse_neg2(i32 *%P) {
   ret void
 }
 
+@c = external global i32, align 4
+declare i32 @reads_c(i32 returned)
+define void @pr28763() {
+entry:
+; CHECK-LABEL: @pr28763(
+; CHECK: store i32 0, i32* @c, align 4
+; CHECK: call i32 @reads_c(i32 0)
+; CHECK: store i32 2, i32* @c, align 4
+  %load = load i32, i32* @c, align 4
+  store i32 0, i32* @c, align 4
+  %call = call i32 @reads_c(i32 0)
+  store i32 2, i32* @c, align 4
+  ret void
+}