Re:Re: [PATCH] [PHIOPT] Add A ? B + CST : B match and simplify optimizations

[钟云德 <zhong_1985624@163.com>]

[-- Attachment #1: Type: text/plain, Size: 3406 bytes --]

At 2022-11-08 22:58:34, "Richard Biener" <richard.guenther@gmail.com> wrote:

>On Sat, Nov 5, 2022 at 10:03 AM Zhongyunde via Gcc-patches
><gcc-patches@gcc.gnu.org> wrote:
>>
>>
>> > -----Original Message-----
>> > From: Andrew Pinski [mailto:pinskia@gcc.gnu.org]
>> > Sent: Saturday, November 5, 2022 2:34 PM
>> > To: Zhongyunde <zhongyunde@huawei.com>
>> > Cc: hongtao.liu@intel.com; gcc-patches@gcc.gnu.org; Zhangwen(Esan)
>> > <zwzhangwen.zhang@huawei.com>; Weiwei (weiwei, Compiler)
>> > <weiwei64@huawei.com>; zhong_1985624@163.com
>> > Subject: Re: [PATCH] [PHIOPT] Add A ? B + CST : B match and simplify
>> > optimizations
>> >
>> > On Fri, Nov 4, 2022 at 11:17 PM Zhongyunde <zhongyunde@huawei.com>
>> > wrote:
>> > >
>> > > hi,
>> > >   This patch is try to fix the issue
>> > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107190,
>> > > would you like to give me some suggestion, thanks.
>> >
>> > This seems like a "simplified" version of
>> > https://gcc.gnu.org/pipermail/gcc-patches/2021-November/584411.html
>> > which just handles power of 2 constants where we know the cond will be
>> > removed.
>> > We could do even more "simplified" of 1 if needed really.
>> > What is the IR before PHI-OPT? Is it just + 1?
>>
>> Thanks for your attention. It is + 4294967296 before PHI-OPT  (See detail https://gcc.godbolt.org/z/6zEc6ja1z)
>> So we should keep matching the power of 2 constants ?
>>
>> > Also your pattern can be simplified to use integer_pow2p in the match part
>> > instead of INTEGER_CST.
>> >
>> Apply your comment, thanks
>
>How does the patch fix the mentioned bug?  match.pd patterns should make things
>"simpler" but x + (a << C') isn't simpler than a ? x + C : x.  It
>looks you are targeting
>PHI-OPT here, so maybe instead extend value_replacement to handle this case,
>it does look similar to the case with neutral/absorbing element there?
>

>Richard.


Thanks. This patch try to fix the 1st issued mentioned in107090 – [aarch64] sequence logic should be combined with mul and umulh (gnu.org)
Sure, I'll take a look at the function value_replacement. 
I have also noticed that the function of two_value_replacement is very close to patch I want to achieve, and it may be easy to extend.
It seems can be expressed equally in match.pd (called by match_simplify_replacement), so how do we
choose where to implement may be better?
```
|
/* Do the replacement of conditional if it can be done.  */if (!early_p                                                                                                                && !diamond_p                                                                                                           && two_value_replacement (bb, bb1, e2, phi, arg0, arg1))                                                              cfgchanged = true;                                                                                          elseif (!diamond_p                                                                                                              && match_simplify_replacement (bb, bb1, e1, e2, phi,                                                                                                   arg0, arg1, early_p))                                                             cfgchanged = true;                                                                                          
|
```
>> > Thanks, >> > Andrew >> >>