[llvm] r277114 - [EarlyCSE] Correctly handle simplified, but live, instructions

[David Majnemer via llvm-commits]

Author: majnemer
Date: Fri Jul 29 00:39:21 2016
New Revision: 277114

URL: http://llvm.org/viewvc/llvm-project?rev=277114&view=rev
Log:
[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.

Modified:
    llvm/trunk/lib/Transforms/Scalar/EarlyCSE.cpp
    llvm/trunk/test/Transforms/EarlyCSE/basic.ll

Modified: llvm/trunk/lib/Transforms/Scalar/EarlyCSE.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/EarlyCSE.cpp?rev=277114&r1=277113&r2=277114&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/EarlyCSE.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/EarlyCSE.cpp Fri Jul 29 00:39:21 2016
@@ -582,6 +582,7 @@ bool EarlyCSE::processNode(DomTreeNode *
     // 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 *
       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.

Modified: llvm/trunk/test/Transforms/EarlyCSE/basic.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/EarlyCSE/basic.ll?rev=277114&r1=277113&r2=277114&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/EarlyCSE/basic.ll (original)
+++ llvm/trunk/test/Transforms/EarlyCSE/basic.ll Fri Jul 29 00:39:21 2016
@@ -276,3 +276,17 @@ define void @dse_neg2(i32 *%P) {
   ret void
 }
 
+ at 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
+}