Re: [Patch] PR 51938: extend ifcombine

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

On Mon, Jul 23, 2012 at 10:58 PM, Marc Glisse <marc.glisse@inria.fr> wrote:
> On Wed, 20 Jun 2012, Richard Guenther wrote:
>
>> On Sun, Jun 10, 2012 at 4:16 PM, Marc Glisse <marc.glisse@inria.fr> wrote:
>>>
>>> Hello,
>>>
>>> currently, tree-ssa-ifcombine handles pairs of imbricated "if"s that
>>> share
>>> the same then branch, or the same else branch. There is no particular
>>> reason
>>> why it couldn't also handle the case where the then branch of one is the
>>> else branch of the other, which is what I do here.
>>>
>>> Any comments?
>>
>>
>> The general idea looks good, but I think the patch is too invasive.  As
>> far
>> as I can see the only callers with a non-zero 'inv' argument come from
>> ifcombine_ifnotorif and ifcombine_ifnotandif (and both with inv == 2).
>> I would rather see a more localized patch that makes use of
>> invert_tree_comparison to perform the inversion on the call arguments
>> of maybe_fold_and/or_comparisons.
>
>
> Hello,
>
> I finally went back to this version (which is where I started from, as shown
> in the PR). It is not very satisfying because:
>
> * some bit tests could also be optimized (more generally, grouping a&&b and
> !a&&b on one side and a||b and !a||b on the other side is rather arbitrary),
>
> * -ftrapping-math makes it useless for floating point,
>
> but I guess it is better than nothing. Handling traps correctly is
> complicated because the current code is already a bit bogus (see
> http://gcc.gnu.org/ml/gcc-patches/2012-07/msg00924.html for an example), and
> even the definition of -ftrapping-math is not clear (
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53805 ).
>
> If defaults are ever reconsidered, my default flags include -frounding-math
> -fno-trapping-math.
>

This patch is ok if bootstrapped / regtested properly.

Thanks,
Richard.

>
> 2012-06-10  Marc Glisse  <marc.glisse@inria.fr>
>
> gcc/
>         PR tree-optimization/51938
>         * tree-ssa-ifcombine.c (ifcombine_ifandif): New parameter for
>         inverted outer condition.
>         (ifcombine_iforif): Likewise.
>         (tree_ssa_ifcombine_bb): Update calls to the above. Detect !a&&b
>         and !a||b patterns.
>
>
> gcc/testsuite/
>         PR tree-optimization/51938
>         * gcc.dg/tree-ssa/ssa-ifcombine-8.c: New testcase.
>         * gcc.dg/tree-ssa/ssa-ifcombine-9.c: New testcase.
>
> --
> Marc Glisse