[clang] Align -ffp-model=fast denormal handling with -ffast-math (PR #89477)

[Fangrui Song via cfe-commits]

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@@ -1314,11 +1314,17 @@ bool ToolChain::isFastMathRuntimeAvailable(const ArgList &Args,
     Arg *A =
       Args.getLastArg(options::OPT_ffast_math, options::OPT_fno_fast_math,
                       options::OPT_funsafe_math_optimizations,
-                      options::OPT_fno_unsafe_math_optimizations);
+                      options::OPT_fno_unsafe_math_optimizations,
+                      options::OPT_ffp_model_EQ);
 
     if (!A || A->getOption().getID() == options::OPT_fno_fast_math ||
         A->getOption().getID() == options::OPT_fno_unsafe_math_optimizations)
       return false;
+    if (A && A->getOption().getID() == options::OPT_ffp_model_EQ) {
+      StringRef Model = A->getValue();
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MaskRay wrote:

Nit: `A->getValue() != "fast"`

inline used-once variable and prefer `==` `!=` for StringRef, which are much more common than `equals`.

https://github.com/llvm/llvm-project/pull/89477