Re: [PATCH] Fix PR83008

[Christophe Lyon <christophe dot lyon at linaro dot org>]

On 30 January 2018 at 11:47, Jakub Jelinek <jakub@redhat.com> wrote:
> On Tue, Jan 30, 2018 at 11:07:50AM +0100, Richard Biener wrote:
>>
>> I have been asked to push this change, fixing (somewhat) the impreciseness
>> of costing constant/invariant vector uses in SLP stmts.  The previous
>> code always just considered a single constant to be generated in the
>> prologue irrespective of how many we'd need.  With this patch we
>> properly handle this count and optimize for the case when we can use
>> a vector splat.  It doesn't yet handle CSE (or CSE among stmts) which
>> means it could in theory regress cases it overall costed correctly
>> before "optimistically" (aka by accident).  But at least the costing
>> now matches code generation.
>>
>> Bootstrapped and tested on x86_64-unknown-linux-gnu.  On x86_64
>> Haswell with AVX2 SPEC 2k6 shows no off-noise changes.
>>
>> The patch is said to help the case in the PR when additional backend
>> costing changes are done (for AVX512).
>>
>> Ok for trunk at this stage?
>
> LGTM.
>
>> 2018-01-30  Richard Biener  <rguenther@suse.de>
>>
>>       PR tree-optimization/83008
>>       * tree-vect-slp.c (vect_analyze_slp_cost_1): Properly cost
>>       invariant and constant vector uses in stmts when they need
>>       more than one stmt.
>
>         Jakub

Hi Richard,

This patch caused a regression on aarch64*:
FAIL: gcc.dg/cse_recip.c scan-tree-dump-times optimized "rdiv_expr" 1
(found 2 times)
we used to have:
PASS: gcc.dg/cse_recip.c scan-tree-dump-times optimized "rdiv_expr" 1

Christophe