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From: "joakim.tjernlund at infinera dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/43892] PowerPC suboptimal "add with carry" optimization
Date: Thu, 03 Jun 2021 07:00:16 +0000 [thread overview]
Message-ID: <bug-43892-4-TGNuWWkuie@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-43892-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43892
--- Comment #34 from Joakim Tjernlund <joakim.tjernlund at infinera dot com> ---
(In reply to Christophe Leroy from comment #28)
> Looks like we have a way to do it. Works at least with GCC 5.5, 8.2, 9.2,
> 10.1
>
> unsigned long g(unsigned long a, unsigned long b)
> {
> unsigned long long s = (unsigned long long)a + (unsigned long long)b;
>
> return (s >> 32) + s;
> }
>
> 00000020 <g>:
> 20: 7c 63 20 14 addc r3,r3,r4
> 24: 7c 63 01 94 addze r3,r3
> 28: 4e 80 00 20 blr
>
Does that work when placed in a loop to?
Something close to the example in the first comment:
for(;len; --len)
sum = add32carry(sum, *++buf);
addic 3, 3, 0 /* clear carry */
.L31:
lwzu 0,4(9)
adde 3, 3, 0 /* add with carry */
bdnz .L31
addze 3, 3 /* add in final carry */
next prev parent reply other threads:[~2021-06-03 7:00 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <bug-43892-4@http.gcc.gnu.org/bugzilla/>
2010-09-29 12:45 ` joakim.tjernlund at transmode dot se
2015-01-18 16:34 ` segher at gcc dot gnu.org
2015-01-18 17:00 ` joakim.tjernlund at transmode dot se
2015-01-18 20:31 ` segher at gcc dot gnu.org
2015-01-18 21:44 ` joakim.tjernlund at transmode dot se
2015-01-18 22:54 ` segher at gcc dot gnu.org
2015-01-19 0:05 ` joakim.tjernlund at transmode dot se
2020-10-20 18:37 ` christophe.leroy at csgroup dot eu
2020-10-20 18:59 ` segher at gcc dot gnu.org
2020-10-20 19:37 ` joakim.tjernlund at infinera dot com
2020-10-21 6:09 ` christophe.leroy at csgroup dot eu
2020-10-21 19:28 ` segher at gcc dot gnu.org
2020-10-21 21:01 ` jakub at gcc dot gnu.org
2020-10-21 21:31 ` segher at gcc dot gnu.org
2021-06-03 1:50 ` pinskia at gcc dot gnu.org
2021-06-03 4:33 ` segher at gcc dot gnu.org
2021-06-03 7:00 ` joakim.tjernlund at infinera dot com [this message]
2021-06-03 19:32 ` segher at gcc dot gnu.org
2021-12-03 19:44 ` roger at nextmovesoftware dot com
2023-06-06 20:14 ` jakub at gcc dot gnu.org
2023-08-29 16:41 ` bergner at gcc dot gnu.org
2023-08-29 17:43 ` roger at nextmovesoftware dot com
2010-04-26 13:33 [Bug rtl-optimization/43892] New: " gcc-bugzilla at gcc dot gnu dot org
2010-05-21 17:42 ` [Bug target/43892] " segher at gcc dot gnu dot org
2010-05-25 21:42 ` joakim dot tjernlund at transmode dot se
2010-05-26 16:46 ` segher at kernel dot crashing dot org
2010-05-26 20:47 ` joakim dot tjernlund at transmode dot se
2010-05-27 1:37 ` dje at gcc dot gnu dot org
2010-05-27 7:33 ` joakim dot tjernlund at transmode dot se
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