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

[Alexander Monakov <amonakov@ispras.ru>]

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On Tue, 21 Mar 2023, Jeff Law via Gcc-patches wrote:

> On 3/21/23 11:00, Qing Zhao via Gcc-patches wrote:
> > 
> >> On Mar 21, 2023, at 12:56 PM, Paul Koning <paulkoning@comcast.net> wrote:
> >>
> >>> On Mar 21, 2023, at 11:01 AM, Qing Zhao via Gcc-patches
> >>> <gcc-patches@gcc.gnu.org> wrote:
> >>>
> >>> ...
> >>> Most of the compiler users are not familiar with language standards, or no
> >>> access to language standards. Without clearly documenting such warnings
> >>> along with the option explicitly, the users have not way to know such
> >>> potential impact.
> >>
> >> With modern highly optimized languages, not knowing the standard is going
> >> to get you in trouble.  There was a wonderful paper from MIT a few years
> >> ago describing all the many ways C can bite you if you don't know the
> >> rules.
> > 
> > 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?

Perplexed,
Alexander