[PATCH][tree-optimization]Optimize combination of comparisons to dec+compare

[Richard Biener]

On Mon, Jan 4, 2021 at 9:50 PM Eugene Rozenfeld
<Eugene.Rozenfeld@microsoft.com> wrote:
>
> Ping.
>
> -----Original Message-----
> From: Eugene Rozenfeld
> Sent: Tuesday, December 22, 2020 3:01 PM
> To: Richard Biener <richard.guenther@gmail.com>; gcc-patches@gcc.gnu.org
> Subject: RE: Optimize combination of comparisons to dec+compare
>
> Re-sending my question and re-attaching the patch.
>
> Richard, can you please clarify your feedback?

Hmm, OK.

The patch is OK.

Thanks,
Richard.


> Thanks,
>
> Eugene
>
> -----Original Message-----
> From: Gcc-patches <gcc-patches-bounces@gcc.gnu.org> On Behalf Of Eugene Rozenfeld via Gcc-patches
> Sent: Tuesday, December 15, 2020 2:06 PM
> To: Richard Biener <richard.guenther@gmail.com>
> Cc: gcc-patches@gcc.gnu.org
> Subject: [EXTERNAL] Re: Optimize combination of comparisons to dec+compare
>
> Richard,
>
> > Do we already handle x < y || x <= CST to x <= y - CST?
>
> That is an invalid transformation: e.g., consider x=3, y=4, CST=2.
> Can you please clarify?
>
> Thanks,
>
> Eugene
>
> -----Original Message-----
> From: Richard Biener <richard.guenther@gmail.com>
> Sent: Thursday, December 10, 2020 12:21 AM
> To: Eugene Rozenfeld <Eugene.Rozenfeld@microsoft.com>
> Cc: gcc-patches@gcc.gnu.org
> Subject: Re: Optimize combination of comparisons to dec+compare
>
> On Thu, Dec 10, 2020 at 1:52 AM Eugene Rozenfeld via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> >
> > This patch adds a pattern for optimizing x < y || x == XXX_MIN to x <=
> > y-1 if y is an integer with TYPE_OVERFLOW_WRAPS.
>
> Do we already handle x < y || x <= CST to x <= y - CST?
> That is, the XXX_MIN case is just a special-case of generic anti-range testing?  For anti-range testing with signed types we pun to unsigned when possible.
>
> > This fixes pr96674.
> >
> > Tested on x86_64-pc-linux-gnu.
> >
> > For this function
> >
> > bool f(unsigned a, unsigned b)
> > {
> >     return (b == 0) | (a < b);
> > }
> >
> > the code without the patch is
> >
> > test   esi,esi
> > sete   al
> > cmp    esi,edi
> > seta   dl
> > or     eax,edx
> > ret
> >
> > the code with the patch is
> >
> > sub    esi,0x1
> > cmp    esi,edi
> > setae  al
> > ret
> >
> > Eugene
> >
> > gcc/
> > PR tree-optimization/96674
> > * match.pd: New pattern x < y || x == XXX_MIN --> x <= y - 1
> >
> > gcc/testsuite
> > * gcc.dg/pr96674.c: New test.
> >