Re: [patch] Fix wrong code with boolean negation

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

On Mon, Jan 21, 2013 at 9:41 AM, Eric Botcazou <ebotcazou@adacore.com> wrote:
> Hi,
>
> this is a regression present in the Ada compiler since 4.5: the issue had been
> latent for ages, but an unrelated streamlining of the IR made it appear.
>
> When make_range_step is invoked on:
>
>   (integer)!b < 0
>
> where b is a boolean, it returns "always true" instead of "always false".
>
> The sequence is as follows:
>
>   (integer)!b < 0   is_true_if   not in [0:0]
>   (integer)!b       is_true_if   not in [0;+inf[
>   !b                is_true_if   not in [0;255]
>   b                 is_true_if       in [0;255]
>
> The wrong step is the last one: when TRUTH_NOT_EXPR is seen in make_range_step
> the "in" value is unconditionally toggled.  Of course that doesn't work in the
> general case, just if the range is the "boolean" range.  As a matter of fact,
> this is explained just below for the comparison operators:
>
>       /* We can only do something if the range is testing for zero
>          and if the second operand is an integer constant.  Note that
>          saying something is "in" the range we make is done by
>          complementing IN_P since it will set in the initial case of
>          being not equal to zero; "out" is leaving it alone.  */
>
> so the fix is to use the zero range condition in the TRUTH_NOT_EXPR case.
>
> Tested on x86_64-suse-linux, OK for mainline?  And for branch(es)?

Ok everywhere.

Thanks,
Richard.

>
> 2013-01-21  Eric Botcazou  <ebotcazou@adacore.com>
>
>         * fold-const.c (make_range_step) <TRUTH_NOT_EXPR>: Bail out if the
>         range isn't testing for zero.
>
>
> 2013-01-21  Eric Botcazou  <ebotcazou@adacore.com>
>
>         * gnat.dg/opt26.adb: New test.
>
>
> --
> Eric Botcazou