Re: [patch] Teach VRP about NAME + CST1 vs CST2 comparison

[Richard Biener <richard dot guenther at gmail dot com>]

On Fri, May 20, 2016 at 11:20 AM, Eric Botcazou <ebotcazou@adacore.com> wrote:
> Hi,
>
> this enhances VRP, more precisely compare_values_warnv, so as not to give up
> for the NAME + CST1 vs CST2 comparison if type overflow is undefined and the
> difference CST2 - CST1 overflows or underflows.  This makes it possible to
> optimize out a class of overflow checks in Ada, typically:
>
> function F (Val, Max : Integer) return Integer is
> begin
>    if Val >= Max then
>       return Max;
>    end if;
>    return Val + 1;  -- overflow check can never fail
> end;
>
> The patch also streamlines the handling of symbolic values in the function by
> calling get_single_symbol instead of doing the decompostion manually twice.
>
> The Ada part is a tweak to expose more opportunities to VRP by removing casts.
>
> Tested on x86_64-suse-linux, OK for the mainline?

Ok.

Thanks,
Richard.

>
> 2016-05-20  Eric Botcazou  <ebotcazou@adacore.com>
>
>         * tree-vrp.c (compare_values_warnv): Simplify handling of symbolic
>         ranges by calling get_single_symbol and tidy up.  Look more closely
>         into NAME + CST1 vs CST2 comparisons if type overflow is undefined.
> ada/
>         * gcc-interface/decl.c (gnat_to_gnu_entity)<E_Signed_Integer_Subtype>
>         Make same-sized subtypes of signed base types signed.
>         * gcc-interface/utils.c (make_type_from_size): Adjust to above
>         change.
>         (unchecked_convert): Likewise.
>
>
> 2016-05-20  Eric Botcazou  <ebotcazou@adacore.com>
>
>         * gnat.dg/opt53.adb: New test.
>         * gnat.dg/opt54.adb: Likewise.
>
> --
> Eric Botcazou