Re: [PATCH] Fix PR 53395: tree-if-conv.c not producing MAX_EXPR

[Andrew Pinski <pinskia at gmail dot com>]

On Mon, May 21, 2012 at 2:56 AM, Richard Guenther
<richard.guenther@gmail.com> wrote:
> On Sun, May 20, 2012 at 1:40 AM, Andrew Pinski <pinskia@gmail.com> wrote:
>> The problem here is that tree-if-conv.c produces COND_EXPR instead of
>> the MAX/MIN EXPRs.  When I added the expansion from COND_EXPR to
>> conditional moves, I assumes that the expressions which should have
>> been converted into MAX_EXPR/MIN_EXPR have already happened.
>>
>> This fixes the problem by having tree-if-conv fold the expression so
>> the MIN_EXPR/MAX_EXPR appears in the IR rather than COND_EXPR and the
>> expansion happens correctly to the min/max rtl rather than just
>> through the conditional move ones.
>>
>> OK?  Bootstrapped and tested on x86_64-linux-gnu with no regressions.
>
> As we are unconditionally building a gimple_assign from the folding result
> you need to re-gimplify it.  The code was using build3 instead of fold_build3
> to avoid that and to make sure we create a plain COND_EXPR we can
> later CSE / simplify properly.  Generating a MAX_EXPR directly is certainly
> fine (can we always vectorize that?), but I suppose simply changing the
> code to use fold_build3 will have unwanted fallout (consider folds habit
> to insert conversions that are not requried on gimple).
>
> So I'd rather prefer to abstract the build3 (COND_EXPR,... into a
> helper function that uses fold_ternary and only if the result is an
> invariant/register or a MIN/MAX_EXPR use the result, canonicalizing
> it properly.

Here is an updated patch which does exactly that.

Note I noticed another regression dealing with my expansion for
COND_EXPR dealing with min/max and I will be submitting patches for
those issue tomorrow.

OK? Bootstrap and tested on x86_64-linux-gnu.

Thanks,
Andrew Pinski

ChangeLog:
* tree-if-conv.c (constant_or_ssa_name): New function.
(fold_build_cond_expr): New function.
(predicate_scalar_phi): Use fold_build_cond_expr instead of build3.
(predicate_mem_writes): Likewise.

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