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Re: GCC and Floating-Point (A proposal)
Allan Sandfeld Jensen wrote:
>>Yes. I still don't understand why gcc doesn't do -ffast-math by
>>default like all other compilers.
Vincent Lefevre wrote:
> No! And I really don't think that other compilers do that.
> It would be very bad, would not conform to the C standard[*]
> and would make lots of codes fail.
Perhaps what needs to be changed is the definition of -ffast-math
itself. Some people (myself included) view it from the standpoint of
using the full capabilities of our processors' hardware intrinsics;
however, -ffast-math *also* implies the rearrangement of code that
violates Standard behavior. Thus it does two things that perhaps should
not be combined.
To be more pointed, it is -funsafe-math-optimizations (implied by
-ffast-math) that is in need of adjustment.
May I be so bold as to suggest that -funsafe-math-optimizations be
reduced in scope to perform exactly what it's name implies:
transformations that may slightly alter the meanding of code. Then move
the use of hardware intrinsics to a new -fhardware-math switch.
Does anyone object if I experiment a bit with this modification? Or am I
completely wrong in my understanding?
..Scott