[clang] [Clang] Fix warning for non std functions with name `infinity` (PR #123417)

[Zahira Ammarguellat via cfe-commits]

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@@ -8454,26 +8454,43 @@ static bool IsInfOrNanFunction(StringRef calleeName, MathCheck Check) {
   llvm_unreachable("unknown MathCheck");
 }
 
+static bool IsInfinityFunction(const FunctionDecl *FDecl) {
+  if (FDecl->getName() != "infinity")
+    return false;
+
+  if (const CXXMethodDecl *MDecl = dyn_cast<CXXMethodDecl>(FDecl)) {
+    const CXXRecordDecl *RDecl = MDecl->getParent();
+    if (RDecl->getName() != "numeric_limits")
+      return false;
+
+    if (const NamespaceDecl *NSDecl =
+            dyn_cast<NamespaceDecl>(RDecl->getDeclContext()))
+      return NSDecl->isStdNamespace();
+  }
+
+  return false;
+}
+
 void Sema::CheckInfNaNFunction(const CallExpr *Call,
                                const FunctionDecl *FDecl) {
+  if (!FDecl->getIdentifier())
+    return;
+
   FPOptions FPO = Call->getFPFeaturesInEffect(getLangOpts());
-  bool HasIdentifier = FDecl->getIdentifier() != nullptr;
-  bool IsNaNOrIsUnordered =
-      IsStdFunction(FDecl, "isnan") || IsStdFunction(FDecl, "isunordered");
-  bool IsSpecialNaN =
-      HasIdentifier && IsInfOrNanFunction(FDecl->getName(), MathCheck::NaN);
-  if ((IsNaNOrIsUnordered || IsSpecialNaN) && FPO.getNoHonorNaNs()) {
+  if (FPO.getNoHonorNaNs() &&
+      (IsStdFunction(FDecl, "isnan") || IsStdFunction(FDecl, "isunordered") ||
+       IsInfOrNanFunction(FDecl->getName(), MathCheck::NaN))) {
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zahiraam wrote:

I think for readability the intermediate `bool` variables can be kept. Same for the condition below.

https://github.com/llvm/llvm-project/pull/123417