[cfe-dev] Best way to determine if preprocessor directives live in a source range?

[Richard]

I'm enhancing clang-tidy to replace:

    if (expr)
      return true;
    return false;

with

    return expr;

I am running the transformation on the LLVM/clang code as a test bed.
In the course of examining the results it turned up this one in
llvm/lib/Analysis/ConstantFolding.cpp:

with

 /// Test if a floating-point exception was raised.
 static inline bool llvm_fenv_testexcept() {
   int errno_val = errno;
-  if (errno_val == ERANGE || errno_val == EDOM)
-    return true;
-#if defined(HAVE_FENV_H) && HAVE_DECL_FE_ALL_EXCEPT && HAVE_DECL_FE_INEXACT
-  if (fetestexcept(FE_ALL_EXCEPT & ~FE_INEXACT))
-    return true;
-#endif
-  return false;
+  return errno_val == ERANGE || errno_val == EDOM;
 }
 } // End namespace

Clearly, this is not behavior preserving.  According to the AST, the
part that is #if'ed out doesn't exist.

What's the best way to identify such things so that the tool's default
behavior would be to leave these alone?

PS: Mail filters are blocking my messages, so ignore this, its
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