[llvm] [DAGCombiner] Remove NoNaNsFPMath uses in visitFADD (PR #163504)

[via llvm-commits]

https://github.com/paperchalice updated https://github.com/llvm/llvm-project/pull/163504

>From 60926c0fabfb0ecd48afd4ffd13a4c3152703582 Mon Sep 17 00:00:00 2001
From: PaperChalice <liujunchang97 at outlook.com>
Date: Wed, 15 Oct 2025 14:17:06 +0800
Subject: [PATCH] [DAGCombiner] Remove NoNaNsFPMath uses

---
 llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 10 +++-------
 llvm/test/CodeGen/ARM/nnan-fsub.ll            | 20 +++++++++++--------
 2 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 358e060d2c6d3..c97300d64d455 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -17759,7 +17759,6 @@ SDValue DAGCombiner::visitFADD(SDNode *N) {
   bool N1CFP = DAG.isConstantFPBuildVectorOrConstantFP(N1);
   EVT VT = N->getValueType(0);
   SDLoc DL(N);
-  const TargetOptions &Options = DAG.getTarget().Options;
   SDNodeFlags Flags = N->getFlags();
   SelectionDAG::FlagInserter FlagsInserter(DAG, N);
 
@@ -17825,7 +17824,7 @@ SDValue DAGCombiner::visitFADD(SDNode *N) {
   bool AllowNewConst = (Level < AfterLegalizeDAG);
 
   // If nnan is enabled, fold lots of things.
-  if ((Options.NoNaNsFPMath || Flags.hasNoNaNs()) && AllowNewConst) {
+  if (Flags.hasNoNaNs() && AllowNewConst) {
     // If allowed, fold (fadd (fneg x), x) -> 0.0
     if (N0.getOpcode() == ISD::FNEG && N0.getOperand(0) == N1)
       return DAG.getConstantFP(0.0, DL, VT);
@@ -17974,7 +17973,6 @@ SDValue DAGCombiner::visitFSUB(SDNode *N) {
   ConstantFPSDNode *N1CFP = isConstOrConstSplatFP(N1, true);
   EVT VT = N->getValueType(0);
   SDLoc DL(N);
-  const TargetOptions &Options = DAG.getTarget().Options;
   const SDNodeFlags Flags = N->getFlags();
   SelectionDAG::FlagInserter FlagsInserter(DAG, N);
 
@@ -18002,7 +18000,7 @@ SDValue DAGCombiner::visitFSUB(SDNode *N) {
 
   if (N0 == N1) {
     // (fsub x, x) -> 0.0
-    if (Options.NoNaNsFPMath || Flags.hasNoNaNs())
+    if (Flags.hasNoNaNs())
       return DAG.getConstantFP(0.0f, DL, VT);
   }
 
@@ -18313,7 +18311,6 @@ template <class MatchContextClass> SDValue DAGCombiner::visitFMA(SDNode *N) {
   ConstantFPSDNode *N2CFP = dyn_cast<ConstantFPSDNode>(N2);
   EVT VT = N->getValueType(0);
   SDLoc DL(N);
-  const TargetOptions &Options = DAG.getTarget().Options;
   // FMA nodes have flags that propagate to the created nodes.
   SelectionDAG::FlagInserter FlagsInserter(DAG, N);
   MatchContextClass matcher(DAG, TLI, N);
@@ -18339,8 +18336,7 @@ template <class MatchContextClass> SDValue DAGCombiner::visitFMA(SDNode *N) {
       return matcher.getNode(ISD::FMA, DL, VT, NegN0, NegN1, N2);
   }
 
-  if ((Options.NoNaNsFPMath && N->getFlags().hasNoInfs()) ||
-      (N->getFlags().hasNoNaNs() && N->getFlags().hasNoInfs())) {
+  if (N->getFlags().hasNoNaNs() && N->getFlags().hasNoInfs()) {
     if (N->getFlags().hasNoSignedZeros() ||
         (N2CFP && !N2CFP->isExactlyValue(-0.0))) {
       if (N0CFP && N0CFP->isZero())
diff --git a/llvm/test/CodeGen/ARM/nnan-fsub.ll b/llvm/test/CodeGen/ARM/nnan-fsub.ll
index 01839083547be..78dd36f954913 100644
--- a/llvm/test/CodeGen/ARM/nnan-fsub.ll
+++ b/llvm/test/CodeGen/ARM/nnan-fsub.ll
@@ -1,18 +1,22 @@
-; RUN: llc -mcpu=cortex-a9 < %s | FileCheck -check-prefix=SAFE %s
-; RUN: llc -mcpu=cortex-a9 --enable-no-nans-fp-math < %s | FileCheck -check-prefix=FAST %s
+; RUN: llc -mcpu=cortex-a9 < %s | FileCheck %s
 
 target triple = "armv7-apple-ios"
 
-; SAFE: test
-; FAST: test
+; CHECK-LABEL: test
 define float @test(float %x, float %y) {
 entry:
-; SAFE: vmul.f32
-; SAFE: vsub.f32
-; FAST: mov r0, #0
+; CHECK: vmul.f32
+; CHECK-NEXT: vsub.f32
   %0 = fmul float %x, %y
   %1 = fsub float %0, %0
   ret float %1
 }
 
-
+; CHECK-LABEL: test_nnan
+define float @test_nnan(float %x, float %y) {
+entry:
+; CHECK: mov r0, #0
+  %0 = fmul float %x, %y
+  %1 = fsub nnan float %0, %0
+  ret float %1
+}