[llvm] [clang] [clang-tools-extra] [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]

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@@ -13861,6 +13897,36 @@ Sema::CheckReturnValExpr(Expr *RetValExp, QualType lhsType,
     CheckPPCMMAType(RetValExp->getType(), ReturnLoc);
 }
 
+/// Diagnose comparison to NAN or INFINITY in fast math modes.
+/// The comparison to NaN or INFINITY is always false in
+/// fast modes: float evaluation will not result in inf or nan.
+void Sema::CheckInfNaNFloatComparison(SourceLocation Loc, Expr *LHS, Expr *RHS,
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AaronBallman wrote:

Why are we on that path in the first place? The token length shouldn't be one character long for either `inf` or `nan` right? I was thinking you should be able to call `NumericLiteralParser::GetFloatValue()` within the `} else if (Literal.isFloatingLiteral()) {` block to get an `APFloat` that you can call `isInfinity()` or `isNaN()` on and then diagnose at that point.

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