[llvm] [InstCombine] Treat identical operands as one in pushFreezeToPreventPoisonFromPropagating (PR #145348)

[Cullen Rhodes via llvm-commits]

https://github.com/c-rhodes updated https://github.com/llvm/llvm-project/pull/145348

>From 97d3aec3c120741f36ec9e3724bfa155f639d82d Mon Sep 17 00:00:00 2001
From: Cullen Rhodes <cullen.rhodes at arm.com>
Date: Mon, 23 Jun 2025 14:30:29 +0000
Subject: [PATCH 1/3] [InstCombine] Precommit test

---
 llvm/test/Transforms/InstCombine/freeze.ll | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/llvm/test/Transforms/InstCombine/freeze.ll b/llvm/test/Transforms/InstCombine/freeze.ll
index 9733f1b732c3f..426c4373a8782 100644
--- a/llvm/test/Transforms/InstCombine/freeze.ll
+++ b/llvm/test/Transforms/InstCombine/freeze.ll
@@ -142,6 +142,17 @@ define i32 @early_freeze_test3(i32 %v1) {
   ret i32 %v4.fr
 }
 
+define i32 @early_freeze_test4(i32 %v1) {
+; CHECK-LABEL: @early_freeze_test4(
+; CHECK-NEXT:    [[V2:%.*]] = mul i32 [[V1_FR:%.*]], [[V1_FR]]
+; CHECK-NEXT:    [[V2_FR:%.*]] = freeze i32 [[V2]]
+; CHECK-NEXT:    ret i32 [[V2_FR]]
+;
+  %v2 = mul i32 %v1, %v1
+  %v2.fr = freeze i32 %v2
+  ret i32 %v2.fr
+}
+
 ; If replace all dominated uses of v to freeze(v).
 
 define void @freeze_dominated_uses_test1(i32 %v) {

>From 10e8258ca73ea709689e0104267935564830986a Mon Sep 17 00:00:00 2001
From: Cullen Rhodes <cullen.rhodes at arm.com>
Date: Mon, 23 Jun 2025 14:34:18 +0000
Subject: [PATCH 2/3] [InstCombine] Treat identical operands as one in
 pushFreezeToPreventPoisonFromPropagating

To push a freeze through an instruction, only one operand may produce
poison. However, this currently fails for identical operands which are
treated as separate. This patch fixes this by treating them as a single
operand.
---
 llvm/lib/Transforms/InstCombine/InstructionCombining.cpp | 4 +++-
 llvm/test/Transforms/InstCombine/freeze.ll               | 6 +++---
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 91a1b61ddc483..8bb4d3bce4a5d 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -4902,7 +4902,9 @@ InstCombinerImpl::pushFreezeToPreventPoisonFromPropagating(FreezeInst &OrigFI) {
   Use *MaybePoisonOperand = nullptr;
   for (Use &U : OrigOpInst->operands()) {
     if (isa<MetadataAsValue>(U.get()) ||
-        isGuaranteedNotToBeUndefOrPoison(U.get()))
+        isGuaranteedNotToBeUndefOrPoison(U.get()) ||
+        // Treat identical operands as a single operand.
+        (MaybePoisonOperand && MaybePoisonOperand->get() == U.get()))
       continue;
     if (!MaybePoisonOperand)
       MaybePoisonOperand = &U;
diff --git a/llvm/test/Transforms/InstCombine/freeze.ll b/llvm/test/Transforms/InstCombine/freeze.ll
index 426c4373a8782..3fedead2feab8 100644
--- a/llvm/test/Transforms/InstCombine/freeze.ll
+++ b/llvm/test/Transforms/InstCombine/freeze.ll
@@ -144,9 +144,9 @@ define i32 @early_freeze_test3(i32 %v1) {
 
 define i32 @early_freeze_test4(i32 %v1) {
 ; CHECK-LABEL: @early_freeze_test4(
-; CHECK-NEXT:    [[V2:%.*]] = mul i32 [[V1_FR:%.*]], [[V1_FR]]
-; CHECK-NEXT:    [[V2_FR:%.*]] = freeze i32 [[V2]]
-; CHECK-NEXT:    ret i32 [[V2_FR]]
+; CHECK-NEXT:    [[V2_FR:%.*]] = freeze i32 [[V2:%.*]]
+; CHECK-NEXT:    [[V3:%.*]] = mul i32 [[V2_FR]], [[V2_FR]]
+; CHECK-NEXT:    ret i32 [[V3]]
 ;
   %v2 = mul i32 %v1, %v1
   %v2.fr = freeze i32 %v2

>From 1e487705d7d393da457799fefde8b5507a4c6f8f Mon Sep 17 00:00:00 2001
From: Cullen Rhodes <cullen.rhodes at arm.com>
Date: Tue, 15 Jul 2025 08:21:05 +0000
Subject: [PATCH 3/3] Switch code from working on Use* to Value* and replace
 all uses

---
 .../Transforms/InstCombine/InstructionCombining.cpp  | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 8bb4d3bce4a5d..0ef6cf893d67e 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -4899,15 +4899,15 @@ InstCombinerImpl::pushFreezeToPreventPoisonFromPropagating(FreezeInst &OrigFI) {
   // 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 guaranteed to be
   // poison.
-  Use *MaybePoisonOperand = nullptr;
+  Value *MaybePoisonOperand = nullptr;
   for (Use &U : OrigOpInst->operands()) {
     if (isa<MetadataAsValue>(U.get()) ||
         isGuaranteedNotToBeUndefOrPoison(U.get()) ||
         // Treat identical operands as a single operand.
-        (MaybePoisonOperand && MaybePoisonOperand->get() == U.get()))
+        (MaybePoisonOperand && MaybePoisonOperand == U.get()))
       continue;
     if (!MaybePoisonOperand)
-      MaybePoisonOperand = &U;
+      MaybePoisonOperand = U.get();
     else
       return nullptr;
   }
@@ -4919,10 +4919,10 @@ InstCombinerImpl::pushFreezeToPreventPoisonFromPropagating(FreezeInst &OrigFI) {
     return OrigOp;
 
   Builder.SetInsertPoint(OrigOpInst);
-  auto *FrozenMaybePoisonOperand = Builder.CreateFreeze(
-      MaybePoisonOperand->get(), MaybePoisonOperand->get()->getName() + ".fr");
+  Value *FrozenMaybePoisonOperand = Builder.CreateFreeze(
+      MaybePoisonOperand, MaybePoisonOperand->getName() + ".fr");
 
-  replaceUse(*MaybePoisonOperand, FrozenMaybePoisonOperand);
+  OrigOpInst->replaceUsesOfWith(MaybePoisonOperand, FrozenMaybePoisonOperand);
   return OrigOp;
 }