Re: Should -ffp-contract=off the default on GCC?

[Richard Biener <richard.guenther@gmail.com>]

On Tue, Mar 21, 2023 at 7:18 PM Jeff Law via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
>
>
> On 3/21/23 12:12, Alexander Monakov wrote:
> >>> Yes, it’s better to know the details of languages standard. -:)
> >>> However, I don’t think that this is a realistic expectation to the compiler
> >>> users:  to know all the details of a language standard.
> >> Umm, they really do need to know that stuff.
> >>
> >> If the developer fails to understand the language standard, then they're
> >> likely going to write code that is ultimately undefined or doesn't behave in
> >> they expect.  How is the compiler supposed to guess what the developer
> >> originally intended?  How should the compiler handle the case when two
> >> developers have different understandings of how a particular piece of code
> >> should work?  In the end it's the language standard that defines how all this
> >> stuff should work.
> >>
> >> Failure to understand the language is a common problem and we do try to emit
> >> various diagnostics to help developers avoid writing non-conformant code.  But
> >> ultimately if a developer fails to understand the language standard, then
> >> they're going to be surprised by the behavior of their code.
> >
> > W h a t.
> >
> > This subthread concerns documenting the option better ("Without clearly
> > documenting such warnings ...").
> >
> > Are you arguing against adding a brief notice to the documentation blurb for
> > the -ffp-contract= option?
> I was merely chiming in on Qing's statement that it is not realistic to
> expect users to know the details of the language standard.

I think it's even less realistic to expect users to know the details of
floating-point math.  So I doubt any such sentence will be helpful
besides spreading some FUD?

>
>
> Jeff