[llvm] WIP: [AMDGPU] Remove `UnsafeFPMath` (PR #151079)

[via llvm-commits]

https://github.com/paperchalice created https://github.com/llvm/llvm-project/pull/151079

None

>From 6258dcb3ee3645743b5c0bd82165c7db5a23c639 Mon Sep 17 00:00:00 2001
From: PaperChalice <liujunchang97 at outlook.com>
Date: Tue, 29 Jul 2025 12:44:26 +0800
Subject: [PATCH] Remove `UnsafeFPMath` in `AMDGPUCodeGenPrepare`

---
 llvm/lib/Target/AMDGPU/AMDGPUCodeGenPrepare.cpp | 15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)

diff --git a/llvm/lib/Target/AMDGPU/AMDGPUCodeGenPrepare.cpp b/llvm/lib/Target/AMDGPU/AMDGPUCodeGenPrepare.cpp
index 5f1983791cfae..7e2c67d22cf6e 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUCodeGenPrepare.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUCodeGenPrepare.cpp
@@ -89,10 +89,6 @@ static cl::opt<bool> DisableFDivExpand(
   cl::ReallyHidden,
   cl::init(false));
 
-static bool hasUnsafeFPMath(const Function &F) {
-  return F.getFnAttribute("unsafe-fp-math").getValueAsBool();
-}
-
 class AMDGPUCodeGenPrepareImpl
     : public InstVisitor<AMDGPUCodeGenPrepareImpl, bool> {
 public:
@@ -104,7 +100,6 @@ class AMDGPUCodeGenPrepareImpl
   const DominatorTree *DT;
   const UniformityInfo &UA;
   const DataLayout &DL;
-  const bool HasUnsafeFPMath;
   const bool HasFP32DenormalFlush;
   bool FlowChanged = false;
   mutable Function *SqrtF32 = nullptr;
@@ -117,7 +112,6 @@ class AMDGPUCodeGenPrepareImpl
                            const DominatorTree *DT, const UniformityInfo &UA)
       : F(F), ST(TM.getSubtarget<GCNSubtarget>(F)), TM(TM), TLI(TLI), AC(AC),
         DT(DT), UA(UA), DL(F.getDataLayout()),
-        HasUnsafeFPMath(hasUnsafeFPMath(F)),
         HasFP32DenormalFlush(SIModeRegisterDefaults(F, ST).FP32Denormals ==
                              DenormalMode::getPreserveSign()) {}
 
@@ -637,8 +631,7 @@ bool AMDGPUCodeGenPrepareImpl::canOptimizeWithRsq(const FPMathOperator *SqrtOp,
     return false;
 
   // v_rsq_f32 gives 1ulp
-  return SqrtFMF.approxFunc() || HasUnsafeFPMath ||
-         SqrtOp->getFPAccuracy() >= 1.0f;
+  return SqrtFMF.approxFunc() || SqrtOp->getFPAccuracy() >= 1.0f;
 }
 
 Value *AMDGPUCodeGenPrepareImpl::optimizeWithRsq(
@@ -664,7 +657,7 @@ Value *AMDGPUCodeGenPrepareImpl::optimizeWithRsq(
     IRBuilder<>::FastMathFlagGuard Guard(Builder);
     Builder.setFastMathFlags(DivFMF | SqrtFMF);
 
-    if ((DivFMF.approxFunc() && SqrtFMF.approxFunc()) || HasUnsafeFPMath ||
+    if ((DivFMF.approxFunc() && SqrtFMF.approxFunc()) ||
         canIgnoreDenormalInput(Den, CtxI)) {
       Value *Result = Builder.CreateUnaryIntrinsic(Intrinsic::amdgcn_rsq, Den);
       // -1.0 / sqrt(x) -> fneg(rsq(x))
@@ -852,7 +845,7 @@ bool AMDGPUCodeGenPrepareImpl::visitFDiv(BinaryOperator &FDiv) {
   // expansion of afn to codegen. The current interpretation is so aggressive we
   // don't need any pre-consideration here when we have better information. A
   // more conservative interpretation could use handling here.
-  const bool AllowInaccurateRcp = HasUnsafeFPMath || DivFMF.approxFunc();
+  const bool AllowInaccurateRcp = DivFMF.approxFunc();
   if (!RsqOp && AllowInaccurateRcp)
     return false;
 
@@ -2026,7 +2019,7 @@ bool AMDGPUCodeGenPrepareImpl::visitSqrt(IntrinsicInst &Sqrt) {
 
   // We're trying to handle the fast-but-not-that-fast case only. The lowering
   // of fast llvm.sqrt will give the raw instruction anyway.
-  if (SqrtFMF.approxFunc() || HasUnsafeFPMath)
+  if (SqrtFMF.approxFunc())
     return false;
 
   const float ReqdAccuracy = FPOp->getFPAccuracy();