Re: [RFC PATCH, i386]: Enable post-reload compare elimination pass

[Uros Bizjak <ubizjak at gmail dot com>]

On Fri, May 12, 2017 at 8:34 PM, Jeff Law <law@redhat.com> wrote:
> On 05/10/2017 01:05 PM, Uros Bizjak wrote:
>>
>> On Wed, May 10, 2017 at 5:18 PM, Uros Bizjak <ubizjak@gmail.com> wrote:
>>>
>>> On Wed, May 10, 2017 at 4:27 PM, Jakub Jelinek <jakub@redhat.com> wrote:
>>>>
>>>> On Tue, May 09, 2017 at 06:06:47PM +0200, Uros Bizjak wrote:
>>>>>
>>>>> Attached patch enables post-reload compare elimination pass by
>>>>> providing expected patterns (duplicates of existing patterns with
>>>>> setters of reg and flags switched in the parallel) for flag setting
>>>>> arithmetic instructions.
>>>>>
>>>>> The merge triggers more than 3000 times during the gcc bootstrap,
>>>>> mostly in cases where intervening memory load or store prevents
>>>>> combine from merging the arithmetic insn and the following compare.
>>>>>
>>>>> Also, some recent linux x86_64 defconfig build results in ~200 merges,
>>>>> removing ~200 test/cmp insns. Not much, but I think the results still
>>>>> warrant the pass to be enabled.
>>>>
>>>>
>>>> Isn't the right fix instead to change the compare-elim.c pass to either
>>>> accept both reg vs. flags orderings in parallel, or both depending
>>>> on some target hook, or change it to the order i386.md and most other
>>>> major targets use and just fix up mn10300/rx (and aarch64?) to use the
>>>> same
>>>> order?
>>
>>
>> Attached patch changes compare-elim.c order to what i386.md expects.
>>
>> Thoughts?
>
> I think with an appropriate change to the canonicalization rules in the
> manual this is fine.
>
> I've got the visium, rx and mn103 patches handy to ensure they don't
> regress.  aarch64 doesn't seem to be affected either way but I didn't
> investigate why -- I expected it to improve with your change.
>
> I'll write up a ChangeLog and commit the mn103, rx and visium changes after
> you commit the compare-elim & documentation bits.

Thanks!

I went ahead and commit the patch without documentation change (which
I plan to submit in a separate patch ASAP), with the following
ChangeLog:

2017-05-12  Uros Bizjak  <ubizjak@gmail.com>

    * compare-elim.c (try_eliminate_compare): Canonicalize
    operation with embedded compare to
    [(set (reg:CCM) (compare:CCM (operation) (immediate)))
     (set (reg) (operation)].

    * config/i386/i386.c (TARGET_FLAGS_REGNUM): New define.

Re-bootstrapped and re-tested on x86_64-linux-gnu {,-m32}.

Committed to mainline SVN.

Uros.

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