Re: gcc compile time support for assumptions

["Richard Guenther" <richard dot guenther at gmail dot com>]

On 18 Jan 2007 07:51:51 -0800, Ian Lance Taylor <iant@google.com> wrote:
> Andrew Haley <aph@redhat.com> writes:
>
> > Ian Lance Taylor writes:
> >  > Abramo Bagnara <abramobagnara@tin.it> writes:
> >  >
> >  > > I'd like to know if gcc has implemented some generic way to help
> >  > > optimizer job by allowing programmers to specify assumptions (or
> >  > > constraints).
> >  >
> >  > The answer is no, there is nothing quite like you describe.
> >  >
> >  > But I think it would be a good idea.
> >
> > Something like this would greatly improve the code generation quality
> > of gcj.  There are a great many assertions that I could pass to VRP
> > and the optimizers: this is invariant, this is less than that, and so
> > on.
>
> Well, internally, we do have ASSERT_EXPR.  It would probably take a
> little work to permit the frontends to generate it, but the optimizers
> should understand it.

Providing a __builtin_assert () function is still one thing on my TODO, we can
derive proper ASSERT_EXPRs from it in VRP even in the -DNDEBUG case.
Of course if the asserts still end up in the source VRP already can derive
information from the IL of the assert code.

Richard.