[PATCH] D105392: [InstCombine] Add optimization to prevent poison from being propagated.

[Hyeongyu Kim via Phabricator via llvm-commits]

hyeongyukim updated this revision to Diff 356400.
hyeongyukim added a comment.

Fix test code.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D105392/new/

https://reviews.llvm.org/D105392

Files:
  llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
  llvm/test/Transforms/InstCombine/freeze.ll


Index: llvm/test/Transforms/InstCombine/freeze.ll
===================================================================
--- llvm/test/Transforms/InstCombine/freeze.ll
+++ llvm/test/Transforms/InstCombine/freeze.ll
@@ -92,10 +92,10 @@
 define i32 @early_freeze_test1(i32 %x, i32 %y) {
 ; CHECK-LABEL: @early_freeze_test1(
 ; CHECK-NEXT:    [[V1:%.*]] = add i32 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[V1_FR:%.*]] = freeze i32 [[V1]]
-; CHECK-NEXT:    [[V2:%.*]] = shl i32 [[V1_FR]], 1
+; CHECK-NEXT:    [[V2:%.*]] = shl i32 [[V1]], 1
 ; CHECK-NEXT:    [[V3:%.*]] = and i32 [[V2]], 2
-; CHECK-NEXT:    ret i32 [[V3]]
+; CHECK-NEXT:    [[V3_FR:%.*]] = freeze i32 [[V3]]
+; CHECK-NEXT:    ret i32 [[V3_FR]]
 ;
   %v1 = add i32 %x, %y
   %v2 = shl i32 %v1, 1
@@ -107,10 +107,10 @@
 define i1 @early_freeze_test2(i32* %ptr) {
 ; CHECK-LABEL: @early_freeze_test2(
 ; CHECK-NEXT:    [[V1:%.*]] = load i32, i32* [[PTR:%.*]], align 4
-; CHECK-NEXT:    [[V1_FR:%.*]] = freeze i32 [[V1]]
-; CHECK-NEXT:    [[V2:%.*]] = and i32 [[V1_FR]], 1
+; CHECK-NEXT:    [[V2:%.*]] = and i32 [[V1]], 1
 ; CHECK-NEXT:    [[COND:%.*]] = icmp eq i32 [[V2]], 0
-; CHECK-NEXT:    ret i1 [[COND]]
+; CHECK-NEXT:    [[COND_FR:%.*]] = freeze i1 [[COND]]
+; CHECK-NEXT:    ret i1 [[COND_FR]]
 ;
   %v1 = load i32, i32* %ptr
   %v2 = and i32 %v1, 1
Index: llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3529,30 +3529,39 @@
   //   Op1.fr = Freeze(Op1)
   //   ... = Inst(Op1.fr, NonPoisonOps...)
   auto* OrigOp = OrigFI.getOperand(0);
-  if (auto *OrigOpInst = dyn_cast<Instruction>(OrigOp)) {
-    if (OrigOpInst->hasOneUse() && !canCreateUndefOrPoison(dyn_cast<Operator>(OrigOp))) {
-      Optional<Use *> MaybePoisonOperand;
-      for (Use &U : OrigOpInst->operands()) {
-        if (isGuaranteedNotToBeUndefOrPoison(U.get()))
-          continue;
-        if (!MaybePoisonOperand)
-          MaybePoisonOperand = &U;
-        else if(MaybePoisonOperand)
-          return nullptr;
-      }
+  auto *OrigOpInst = dyn_cast<Instruction>(OrigOp);
 
-      if (!MaybePoisonOperand.hasValue())
-        return nullptr;
+  if (!OrigOpInst)
+    return nullptr;
 
-      auto *MaybePoisonUse = MaybePoisonOperand.getValue();
-      auto *FrozenMaybePoisonOperand = new FreezeInst(MaybePoisonUse->get(), MaybePoisonUse->getUser()->getName() + ".fr");
+  if (!OrigOpInst->hasOneUse() ||
+      canCreateUndefOrPoison(dyn_cast<Operator>(OrigOp)))
+    return nullptr;
 
-      replaceUse(*MaybePoisonUse, FrozenMaybePoisonOperand);
-      FrozenMaybePoisonOperand->insertBefore(OrigOpInst);
-      return OrigOp;
-    }
+  // If operand is guaranteed not to be poison, there is no need to add freeze
+  // to the operand. So we first find the operand that is not guranteed to be
+  // poison.
+  Use *MaybePoisonOperand;
+  for (Use &U : OrigOpInst->operands()) {
+    if (isGuaranteedNotToBeUndefOrPoison(U.get()))
+      continue;
+    if (!MaybePoisonOperand)
+      MaybePoisonOperand = &U;
+    else
+      return nullptr;
   }
-  return nullptr;
+
+  // If all operands are guaranteed to be non-poison, we can drop freeze.
+  if (!MaybePoisonOperand)
+    return OrigOp;
+
+  auto *FrozenMaybePoisonOperand =
+      new FreezeInst(MaybePoisonOperand->get(),
+                     MaybePoisonOperand->getUser()->getName() + ".fr");
+
+  replaceUse(*MaybePoisonOperand, FrozenMaybePoisonOperand);
+  FrozenMaybePoisonOperand->insertBefore(OrigOpInst);
+  return OrigOp;
 }
 
 Instruction *InstCombinerImpl::visitFreeze(FreezeInst &I) {


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