[llvm] [IR] Add getFMFFromFnAttribute() to derive fast-math flags from function attributes. nfc (PR #162628)

[Mel Chen via llvm-commits]

https://github.com/Mel-Chen created https://github.com/llvm/llvm-project/pull/162628

None

>From 397178e3f0573fba810a180ae8c1a6899d017994 Mon Sep 17 00:00:00 2001
From: Mel Chen <mel.chen at sifive.com>
Date: Thu, 9 Oct 2025 01:12:00 -0700
Subject: [PATCH] [Function] Add getFMFFromFnAttribute() to derive
 FastMathFlags from function attributes. nfc

---
 llvm/include/llvm/IR/Function.h     | 3 +++
 llvm/lib/Analysis/IVDescriptors.cpp | 6 +-----
 llvm/lib/IR/Function.cpp            | 8 ++++++++
 3 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/llvm/include/llvm/IR/Function.h b/llvm/include/llvm/IR/Function.h
index d3497716ca844..21e9d5ea9d066 100644
--- a/llvm/include/llvm/IR/Function.h
+++ b/llvm/include/llvm/IR/Function.h
@@ -470,6 +470,9 @@ class LLVM_ABI Function : public GlobalObject, public ilist_node<Function> {
     return AttributeSets.getFnStackAlignment();
   }
 
+  /// Derive fast-math flags from the function attributes.
+  FastMathFlags getFMFFromFnAttribute() const;
+
   /// Returns true if the function has ssp, sspstrong, or sspreq fn attrs.
   bool hasStackProtectorFnAttr() const;
 
diff --git a/llvm/lib/Analysis/IVDescriptors.cpp b/llvm/lib/Analysis/IVDescriptors.cpp
index b8c540ce4b99d..9b842d6ab37c5 100644
--- a/llvm/lib/Analysis/IVDescriptors.cpp
+++ b/llvm/lib/Analysis/IVDescriptors.cpp
@@ -998,11 +998,7 @@ bool RecurrenceDescriptor::isReductionPHI(PHINode *Phi, Loop *TheLoop,
                                           ScalarEvolution *SE) {
   BasicBlock *Header = TheLoop->getHeader();
   Function &F = *Header->getParent();
-  FastMathFlags FMF;
-  FMF.setNoNaNs(
-      F.getFnAttribute("no-nans-fp-math").getValueAsBool());
-  FMF.setNoSignedZeros(
-      F.getFnAttribute("no-signed-zeros-fp-math").getValueAsBool());
+  FastMathFlags FMF = F.getFMFFromFnAttribute();
 
   if (AddReductionVar(Phi, RecurKind::Add, TheLoop, FMF, RedDes, DB, AC, DT,
                       SE)) {
diff --git a/llvm/lib/IR/Function.cpp b/llvm/lib/IR/Function.cpp
index fc067459dcba3..d2b41c1c9c2ab 100644
--- a/llvm/lib/IR/Function.cpp
+++ b/llvm/lib/IR/Function.cpp
@@ -784,6 +784,14 @@ uint64_t Function::getFnAttributeAsParsedInteger(StringRef Name,
   return Result;
 }
 
+FastMathFlags Function::getFMFFromFnAttribute() const {
+  FastMathFlags FuncFMF;
+  FuncFMF.setNoNaNs(getFnAttribute("no-nans-fp-math").getValueAsBool());
+  FuncFMF.setNoSignedZeros(
+      getFnAttribute("no-signed-zeros-fp-math").getValueAsBool());
+  return FuncFMF;
+}
+
 /// gets the specified attribute from the list of attributes.
 Attribute Function::getParamAttribute(unsigned ArgNo,
                                       Attribute::AttrKind Kind) const {