[llvm] [NVPTX] Remove `UnsafeFPMath` uses (PR #151479)

[via llvm-commits]

https://github.com/paperchalice created https://github.com/llvm/llvm-project/pull/151479

Remove `UnsafeFPMath` in AMDGPU part, it blocks some bugfixes related to clang and the ultimate goal is to remove `resetTargetOptions` method in `TargetMachine`, see FIXME in `resetTargetOptions`.
See also https://discourse.llvm.org/t/rfc-honor-pragmas-with-ffp-contract-fast
https://discourse.llvm.org/t/allowfpopfusion-vs-sdnodeflags-hasallowcontract 

>From 9695804bc2c58a0fdc97ac31f61bb35a0ec1361d Mon Sep 17 00:00:00 2001
From: PaperChalice <liujunchang97 at outlook.com>
Date: Thu, 31 Jul 2025 17:27:13 +0800
Subject: [PATCH] Remove UnsafeFPMath uses

---
 llvm/lib/Target/NVPTX/NVPTXISelDAGToDAG.cpp |  5 ----
 llvm/lib/Target/NVPTX/NVPTXISelDAGToDAG.h   |  1 -
 llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp | 27 +++------------------
 llvm/lib/Target/NVPTX/NVPTXISelLowering.h   |  1 -
 llvm/lib/Target/NVPTX/NVPTXInstrInfo.td     |  5 ++--
 5 files changed, 6 insertions(+), 33 deletions(-)

diff --git a/llvm/lib/Target/NVPTX/NVPTXISelDAGToDAG.cpp b/llvm/lib/Target/NVPTX/NVPTXISelDAGToDAG.cpp
index 95abcded46485..cf9758c80c5c2 100644
--- a/llvm/lib/Target/NVPTX/NVPTXISelDAGToDAG.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXISelDAGToDAG.cpp
@@ -82,11 +82,6 @@ bool NVPTXDAGToDAGISel::allowFMA() const {
   return TL->allowFMA(*MF, OptLevel);
 }
 
-bool NVPTXDAGToDAGISel::allowUnsafeFPMath() const {
-  const NVPTXTargetLowering *TL = Subtarget->getTargetLowering();
-  return TL->allowUnsafeFPMath(*MF);
-}
-
 bool NVPTXDAGToDAGISel::doRsqrtOpt() const { return EnableRsqrtOpt; }
 
 /// Select - Select instructions not customized! Used for
diff --git a/llvm/lib/Target/NVPTX/NVPTXISelDAGToDAG.h b/llvm/lib/Target/NVPTX/NVPTXISelDAGToDAG.h
index 9e0f88e544980..dd05c4df8a3ee 100644
--- a/llvm/lib/Target/NVPTX/NVPTXISelDAGToDAG.h
+++ b/llvm/lib/Target/NVPTX/NVPTXISelDAGToDAG.h
@@ -44,7 +44,6 @@ class LLVM_LIBRARY_VISIBILITY NVPTXDAGToDAGISel : public SelectionDAGISel {
   bool usePrecSqrtF32(const SDNode *N) const;
   bool useF32FTZ() const;
   bool allowFMA() const;
-  bool allowUnsafeFPMath() const;
   bool doRsqrtOpt() const;
 
   NVPTXScopes Scopes{};
diff --git a/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp b/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
index 4fd362303b6e5..16a5cf71f44cd 100644
--- a/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp
@@ -125,10 +125,6 @@ NVPTXTargetLowering::getDivF32Level(const MachineFunction &MF,
   if (UsePrecDivF32.getNumOccurrences() > 0)
     return UsePrecDivF32;
 
-  // Otherwise, use div.approx if fast math is enabled
-  if (allowUnsafeFPMath(MF))
-    return NVPTX::DivPrecisionLevel::Approx;
-
   const SDNodeFlags Flags = N.getFlags();
   if (Flags.hasApproximateFuncs())
     return NVPTX::DivPrecisionLevel::Approx;
@@ -142,10 +138,6 @@ bool NVPTXTargetLowering::usePrecSqrtF32(const MachineFunction &MF,
   if (UsePrecSqrtF32.getNumOccurrences() > 0)
     return UsePrecSqrtF32;
 
-  // Otherwise, use sqrt.approx if fast math is enabled
-  if (allowUnsafeFPMath(MF))
-    return false;
-
   if (N) {
     const SDNodeFlags Flags = N->getFlags();
     if (Flags.hasApproximateFuncs())
@@ -2687,8 +2679,7 @@ static SDValue lowerROT(SDValue Op, SelectionDAG &DAG) {
                      SDLoc(Op), Opcode, DAG);
 }
 
-static SDValue lowerFREM(SDValue Op, SelectionDAG &DAG,
-                         bool AllowUnsafeFPMath) {
+static SDValue lowerFREM(SDValue Op, SelectionDAG &DAG) {
   // Lower (frem x, y) into (sub x, (mul (ftrunc (div x, y)) y)),
   // i.e. "poor man's fmod()". When y is infinite, x is returned. This matches
   // the semantics of LLVM's frem.
@@ -2705,7 +2696,7 @@ static SDValue lowerFREM(SDValue Op, SelectionDAG &DAG,
   SDValue Sub = DAG.getNode(ISD::FSUB, DL, Ty, X, Mul,
                             Flags | SDNodeFlags::AllowContract);
 
-  if (AllowUnsafeFPMath || Flags.hasNoInfs())
+  if (Flags.hasNoInfs())
     return Sub;
 
   // If Y is infinite, return X
@@ -2845,7 +2836,7 @@ NVPTXTargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
   case ISD::CTLZ:
     return lowerCTLZCTPOP(Op, DAG);
   case ISD::FREM:
-    return lowerFREM(Op, DAG, allowUnsafeFPMath(DAG.getMachineFunction()));
+    return lowerFREM(Op, DAG);
 
   default:
     llvm_unreachable("Custom lowering not defined for operation");
@@ -4718,17 +4709,7 @@ bool NVPTXTargetLowering::allowFMA(MachineFunction &MF,
   if (MF.getTarget().Options.AllowFPOpFusion == FPOpFusion::Fast)
     return true;
 
-  return allowUnsafeFPMath(MF);
-}
-
-bool NVPTXTargetLowering::allowUnsafeFPMath(const MachineFunction &MF) const {
-  // Honor TargetOptions flags that explicitly say unsafe math is okay.
-  if (MF.getTarget().Options.UnsafeFPMath)
-    return true;
-
-  // Allow unsafe math if unsafe-fp-math attribute explicitly says so.
-  const Function &F = MF.getFunction();
-  return F.getFnAttribute("unsafe-fp-math").getValueAsBool();
+  return false;
 }
 
 static bool isConstZero(const SDValue &Operand) {
diff --git a/llvm/lib/Target/NVPTX/NVPTXISelLowering.h b/llvm/lib/Target/NVPTX/NVPTXISelLowering.h
index cf72a1e6db89c..71c15695b1988 100644
--- a/llvm/lib/Target/NVPTX/NVPTXISelLowering.h
+++ b/llvm/lib/Target/NVPTX/NVPTXISelLowering.h
@@ -215,7 +215,6 @@ class NVPTXTargetLowering : public TargetLowering {
   unsigned combineRepeatedFPDivisors() const override { return 2; }
 
   bool allowFMA(MachineFunction &MF, CodeGenOptLevel OptLevel) const;
-  bool allowUnsafeFPMath(const MachineFunction &MF) const;
 
   bool isFMAFasterThanFMulAndFAdd(const MachineFunction &MF,
                                   EVT) const override {
diff --git a/llvm/lib/Target/NVPTX/NVPTXInstrInfo.td b/llvm/lib/Target/NVPTX/NVPTXInstrInfo.td
index 6000b40694763..020d42f217f75 100644
--- a/llvm/lib/Target/NVPTX/NVPTXInstrInfo.td
+++ b/llvm/lib/Target/NVPTX/NVPTXInstrInfo.td
@@ -1181,9 +1181,8 @@ defm FMA_F64    : FMA<F64RT,    allow_ftz = false>;
 // sin/cos/tanh
 
 class UnaryOpAllowsApproxFn<SDPatternOperator operator>
-    : PatFrag<(ops node:$A),
-              (operator node:$A), [{
-  return allowUnsafeFPMath() || N->getFlags().hasApproximateFuncs();
+    : PatFrag<(ops node:$A), (operator node:$A), [{
+  return N->getFlags().hasApproximateFuncs();
 }]>;
 
 def SIN_APPROX_f32 :