[llvm] [InstCombine] Fix FMF propagation in `copysign Mag, (copysign ?, X) -> copysign Mag, X` (PR #121574)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/121574

Closes https://github.com/llvm/llvm-project/issues/121432.


>From d29db5d57e2fadf998f9d10fb4877608b5ff8f97 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Fri, 3 Jan 2025 22:10:04 +0800
Subject: [PATCH 1/2] [InstCombine] Add pre-commit tests. NFC.

---
 llvm/test/Transforms/InstCombine/copysign.ll | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/llvm/test/Transforms/InstCombine/copysign.ll b/llvm/test/Transforms/InstCombine/copysign.ll
index abc707acf0cd3f..07175f8405bf28 100644
--- a/llvm/test/Transforms/InstCombine/copysign.ll
+++ b/llvm/test/Transforms/InstCombine/copysign.ll
@@ -90,6 +90,16 @@ define float @copysign_sign_arg(float %x, float %y, float %z) {
   ret float %r
 }
 
+define float @copysign_sign_arg_nnan(float %x, float %y, float %z) {
+; CHECK-LABEL: @copysign_sign_arg_nnan(
+; CHECK-NEXT:    [[R:%.*]] = call nnan float @llvm.copysign.f32(float [[X:%.*]], float [[Z:%.*]])
+; CHECK-NEXT:    ret float [[R]]
+;
+  %s = call nnan float @llvm.copysign.f32(float %y, float %z)
+  %r = call nnan float @llvm.copysign.f32(float %x, float %s)
+  ret float %r
+}
+
 define float @fneg_mag(float %x, float %y) {
 ; CHECK-LABEL: @fneg_mag(
 ; CHECK-NEXT:    [[R:%.*]] = call float @llvm.copysign.f32(float [[X:%.*]], float [[Y:%.*]])

>From 0faae17e4d393a263678a1243cf48a6f3d2a6d0c Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Fri, 3 Jan 2025 22:25:27 +0800
Subject: [PATCH 2/2] [InstCombine] Fix FMF propagation in `copysign Mag,
 (copysign ?, X) -> copysign Mag, X`

---
 llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp | 4 +++-
 llvm/test/Transforms/InstCombine/copysign.ll         | 2 +-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index fd38738e3be80b..6624a40a781d9f 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -2644,8 +2644,10 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
     // Propagate sign argument through nested calls:
     // copysign Mag, (copysign ?, X) --> copysign Mag, X
     Value *X;
-    if (match(Sign, m_Intrinsic<Intrinsic::copysign>(m_Value(), m_Value(X))))
+    if (match(Sign, m_Intrinsic<Intrinsic::copysign>(m_Value(), m_Value(X)))) {
+      II->andIRFlags(Sign);
       return replaceOperand(*II, 1, X);
+    }
 
     // Clear sign-bit of constant magnitude:
     // copysign -MagC, X --> copysign MagC, X
diff --git a/llvm/test/Transforms/InstCombine/copysign.ll b/llvm/test/Transforms/InstCombine/copysign.ll
index 07175f8405bf28..2c92557534708c 100644
--- a/llvm/test/Transforms/InstCombine/copysign.ll
+++ b/llvm/test/Transforms/InstCombine/copysign.ll
@@ -82,7 +82,7 @@ define float @not_known_positive_sign_arg(float %x, float %y) {
 
 define float @copysign_sign_arg(float %x, float %y, float %z) {
 ; CHECK-LABEL: @copysign_sign_arg(
-; CHECK-NEXT:    [[R:%.*]] = call ninf float @llvm.copysign.f32(float [[X:%.*]], float [[Z:%.*]])
+; CHECK-NEXT:    [[R:%.*]] = call float @llvm.copysign.f32(float [[X:%.*]], float [[Z:%.*]])
 ; CHECK-NEXT:    ret float [[R]]
 ;
   %s = call reassoc float @llvm.copysign.f32(float %y, float %z)