fast_math_flags_set_p vs. set_fast_math_flags inconsistency?

Joseph Myers
Tue Jan 28 17:19:00 GMT 2020

On Mon, 27 Jan 2020, Ulrich Weigand wrote:

> I see.  I guess that makes me wonder what -fno-fast-math *ever* does
> (except canceling a -ffast-math earlier on the command line).  Looking
> at the current code, -fno-fast-math (just like -ffast-math) only ever
> sets flags whose default is not overridden on the command line, but
> then it always sets them to their default value!

As a general principle, more specific flags take precedence over less 
specific ones, regardless of the command-line order.  So it's correct for 
-ffast-math and -fno-fast-math not to do anything with a flag that was 
explicitly overridden by the user (modulo any issues where a particular 
combination of flags is unsupported by GCC, as with the 
"%<-fassociative-math%> disabled; other options take precedence" case in 

Joseph S. Myers

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