[clang] [CLANG] Add warning when INF or NAN are used in a binary operation or as function argument in fast math mode. (PR #76873)

[Aaron Ballman via cfe-commits]

================
@@ -9090,10 +9092,16 @@ bool Sema::SemaBuiltinVAStartARMMicrosoft(CallExpr *Call) {
 
 /// SemaBuiltinUnorderedCompare - Handle functions like __builtin_isgreater and
 /// friends.  This is declared to take (...), so we have to check everything.
-bool Sema::SemaBuiltinUnorderedCompare(CallExpr *TheCall) {
+bool Sema::SemaBuiltinUnorderedCompare(CallExpr *TheCall, unsigned BuiltinID) {
   if (checkArgCount(*this, TheCall, 2))
     return true;
 
+  if (BuiltinID == Builtin::BI__builtin_isunordered) {
+    if (TheCall->getFPFeaturesInEffect(getLangOpts()).getNoHonorNaNs())
+      Diag(TheCall->getBeginLoc(), diag::warn_fast_floatingpoint_eq)
+          << "NaN" << TheCall->getSourceRange();
+  }
----------------
AaronBallman wrote:

```suggestion
  if (BuiltinID == Builtin::BI__builtin_isunordered &&
      TheCall->getFPFeaturesInEffect(getLangOpts()).getNoHonorNaNs())
        Diag(TheCall->getBeginLoc(), diag::warn_fast_floatingpoint_eq)
            << "NaN" << TheCall->getSourceRange();
```

https://github.com/llvm/llvm-project/pull/76873