Re: What is acceptable for -ffast-math? (Was: associative law incombine)

[Linus Torvalds <torvalds at transmeta dot com>]

On Sun, 29 Jul 2001 dewar@gnat.com wrote:
>
> <<Further, GCC is supposed to be standards compliant by default.  You
> seem to be advocating that GCC should, without warning, generate
> programs that violate the standard and are mathematically wrong.
> >>
>
> and that violate the expectations of programmers who *do* know what they
> are doing!

Note that most of the people I know who _do_ know what they are doing also
want to have the option o ftelling the compiler when they don't care, and
want to allow the compiler to do "illegal" things if that allows the
compiler to generate better code.

It's sad that C99 doesn't seem to allow the Fortran kind of "you go and
make the best you can of this expression unless I tell you otherwise".
Which means that we'd _have_ to be non-standard to allow the optimization
at all. Which obviously means a flag (one way or the other).

Rather than have a good way to do it on a case-by-case basis, which is
probably what the people who _really_ care would prefer.

In C, you can't reasonably use the Fortran "parenthesis are significant"
approach - the way the C pre-processor works you often have lots of extra
parenthesis for that reason. However, C does have the well-established
sequence point rule, so it would make sense to have that kind of
extension.

And hey, if you want to make it be an extra flag, just make it a _simple_
one. Like "-ffast-math". Don't make people have to know 100 esoteric flags
that are compiler-release-specific. That's completely useless.

		Linus