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

[Richard Biener <richard.guenther@gmail.com>]

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,
> > Andrew
>
>