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From: Richard Biener <rguenther@suse.de>
To: Tamar Christina <Tamar.Christina@arm.com>
Cc: Richard Biener <richard.guenther@gmail.com>,
	 Richard Sandiford <Richard.Sandiford@arm.com>,
	 Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org>,
	nd <nd@arm.com>
Subject: RE: [PATCH 1/2]middle-end: Simplify subtract where both arguments are being bitwise inverted.
Date: Thu, 4 Aug 2022 06:58:06 +0000 (UTC)	[thread overview]
Message-ID: <nycvar.YFH.7.77.849.2208040657520.4208@jbgna.fhfr.qr> (raw)
In-Reply-To: <VI1PR08MB5325FAFF53BB18E6909751CAFF9C9@VI1PR08MB5325.eurprd08.prod.outlook.com>

On Wed, 3 Aug 2022, Tamar Christina wrote:

> > -----Original Message-----
> > From: Richard Biener <richard.guenther@gmail.com>
> > Sent: Tuesday, June 21, 2022 8:43 AM
> > To: Tamar Christina <Tamar.Christina@arm.com>
> > Cc: Richard Sandiford <Richard.Sandiford@arm.com>; Richard Biener via Gcc-
> > patches <gcc-patches@gcc.gnu.org>; Richard Guenther
> > <rguenther@suse.de>; nd <nd@arm.com>
> > Subject: Re: [PATCH 1/2]middle-end: Simplify subtract where both
> > arguments are being bitwise inverted.
> > 
> > On Mon, Jun 20, 2022 at 10:49 AM Tamar Christina
> > <Tamar.Christina@arm.com> wrote:
> > >
> > > > -----Original Message-----
> > > > From: Richard Sandiford <richard.sandiford@arm.com>
> > > > Sent: Monday, June 20, 2022 9:19 AM
> > > > To: Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org>
> > > > Cc: Tamar Christina <Tamar.Christina@arm.com>; Richard Biener
> > > > <richard.guenther@gmail.com>; Richard Guenther
> > <rguenther@suse.de>;
> > > > nd <nd@arm.com>
> > > > Subject: Re: [PATCH 1/2]middle-end: Simplify subtract where both
> > > > arguments are being bitwise inverted.
> > > >
> > > > Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> > > > > On Thu, Jun 16, 2022 at 1:10 PM Tamar Christina via Gcc-patches
> > > > > <gcc-patches@gcc.gnu.org> wrote:
> > > > >>
> > > > >> Hi All,
> > > > >>
> > > > >> This adds a match.pd rule that drops the bitwwise nots when both
> > > > >> arguments to a subtract is inverted. i.e. for:
> > > > >>
> > > > >> float g(float a, float b)
> > > > >> {
> > > > >>   return ~(int)a - ~(int)b;
> > > > >> }
> > > > >>
> > > > >> we instead generate
> > > > >>
> > > > >> float g(float a, float b)
> > > > >> {
> > > > >>   return (int)a - (int)b;
> > > > >> }
> > > > >>
> > > > >> We already do a limited version of this from the fold_binary fold
> > > > >> functions but this makes a more general version in match.pd that
> > > > >> applies
> > > > more often.
> > > > >>
> > > > >> Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.
> > > > >>
> > > > >> Ok for master?
> > > > >>
> > > > >> Thanks,
> > > > >> Tamar
> > > > >>
> > > > >> gcc/ChangeLog:
> > > > >>
> > > > >>         * match.pd: New bit_not rule.
> > > > >>
> > > > >> gcc/testsuite/ChangeLog:
> > > > >>
> > > > >>         * gcc.dg/subnot.c: New test.
> > > > >>
> > > > >> --- inline copy of patch --
> > > > >> diff --git a/gcc/match.pd b/gcc/match.pd index
> > > > >>
> > > >
> > a59b6778f661cf9121dd3503f43472871e4da445..51b0a1b562409af535e53828a1
> > > > 0
> > > > >> c30b8a3e1ae2e 100644
> > > > >> --- a/gcc/match.pd
> > > > >> +++ b/gcc/match.pd
> > > > >> @@ -1258,6 +1258,10 @@ DEFINE_INT_AND_FLOAT_ROUND_FN
> > (RINT)
> > > > >> (simplify
> > > > >>   (bit_not (plus:c (bit_not @0) @1))
> > > > >>   (minus @0 @1))
> > > > >> +/* (~X - ~Y) -> X - Y.  */
> > > > >> +(simplify
> > > > >> + (minus (bit_not @0) (bit_not @1))  (minus @0 @1))
> > > > >
> > > > > It doesn't seem correct.
> > > > >
> > > > > (gdb) p/x ~-1 - ~0x80000000
> > > > > $3 = 0x80000001
> > > > > (gdb) p/x -1 - 0x80000000
> > > > > $4 = 0x7fffffff
> > > > >
> > > > > where I was looking for a case exposing undefined integer overflow.
> > > >
> > > > Yeah, shouldn't it be folding to (minus @1 @0) instead?
> > > >
> > > >   ~X = (-X - 1)
> > > >   -Y = (-Y - 1)
> > > >
> > > > so:
> > > >
> > > >   ~X - ~Y = (-X - 1) - (-Y - 1)
> > > >           = -X - 1 + Y + 1
> > > >           = Y - X
> > > >
> > >
> > > You're right, sorry, I should have paid more attention when I wrote the
> > patch.
> > 
> > You still need to watch out for undefined overflow cases in the result that
> > were well-defined in the original expression I think.
> 
> The only special thing we do for signed numbers if to do the subtract as unsigned.  As I mentioned
> before GCC already does this transformation as part of the fold machinery, but that only only happens
> when a very simple tree is matched and only when single use. i.e. https://godbolt.org/z/EWsdhfrKj
> 
> I'm only attempting to make it apply more generally as the result is always beneficial.
> 
> I've respun the patch to the same as we already do.
> 
> Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.
> 
> Ok for master?

OK.

> Thanks,
> Tamar
> 
> gcc/ChangeLog:
> 
> 	* match.pd: New bit_not rule.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* gcc.dg/subnot.c: New test.
> 
> --- inline copy of patch ---
> 
> diff --git a/gcc/match.pd b/gcc/match.pd
> index 330c1db0c8e12b0fb010b1958729444672403866..00b3e07b2a5216b19ed58500923680d83c67d8cf 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -1308,6 +1308,11 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>  (simplify
>   (bit_not (plus:c (bit_not @0) @1))
>   (minus @0 @1))
> +/* (~X - ~Y) -> Y - X.  */
> +(simplify
> + (minus (bit_not @0) (bit_not @1))
> +  (with { tree utype = unsigned_type_for (type); }
> +   (convert (minus (convert:utype @1) (convert:utype @0)))))
>  
>  /* ~(X - Y) -> ~X + Y.  */
>  (simplify
> diff --git a/gcc/testsuite/gcc.dg/subnot.c b/gcc/testsuite/gcc.dg/subnot.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..d621bacd27bd3d19a010e4c9f831aa77d28bd02d
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/subnot.c
> @@ -0,0 +1,9 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O -fdump-tree-optimized" } */
> +
> +float g(float a, float b)
> +{
> +  return ~(int)a - ~(int)b;
> +}
> +
> +/* { dg-final { scan-tree-dump-not "~" "optimized" } } */
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
HRB 36809 (AG Nuernberg)

      reply	other threads:[~2022-08-04  6:58 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-16 11:08 Tamar Christina
2022-06-16 11:09 ` [PATCH 2/2]middle-end: Support recognition of three-way max/min Tamar Christina
2022-06-20  8:36   ` Richard Biener
2022-06-20  9:01     ` Tamar Christina
2022-06-21 13:15       ` Richard Biener
2022-06-21 13:42         ` Tamar Christina
2022-06-27  7:52           ` Richard Biener
2022-07-05 15:25     ` Tamar Christina
2022-07-12  9:39       ` Tamar Christina
2022-07-12 13:19       ` Richard Biener
2022-07-27 10:40         ` Tamar Christina
2022-07-27 11:18           ` Richard Biener
2022-08-02  8:32             ` Tamar Christina
2022-08-02  9:11               ` Richard Biener
2022-08-03  8:17                 ` Tamar Christina
2022-08-03  8:25                   ` Richard Biener
2022-08-03 20:41                     ` H.J. Lu
2022-06-20 23:16   ` Andrew Pinski
2022-06-21  6:54     ` Richard Biener
2022-06-21  7:12     ` Tamar Christina
2022-06-20  8:03 ` [PATCH 1/2]middle-end: Simplify subtract where both arguments are being bitwise inverted Richard Biener
2022-06-20  8:18   ` Richard Sandiford
2022-06-20  8:49     ` Tamar Christina
2022-06-21  7:43       ` Richard Biener
2022-08-03 15:13         ` Tamar Christina
2022-08-04  6:58           ` Richard Biener [this message]

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