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From: "segher at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/43892] PowerPC suboptimal "add with carry" optimization
Date: Sun, 18 Jan 2015 22:54:00 -0000	[thread overview]
Message-ID: <bug-43892-4-93T3XgWJjW@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 #23 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Do you know what addcc does?  PowerPC does not have any instruction
that behaves like it at all.  So it would have to expand to a big
fat sequence of instructions, that then hopefully are optimised to
something sane later.  Instead, the current code expands to something
sane immediately.

The problem for this testcase (as for all other similar "manual carry"
cases) is that we need to replace the carry in our original patterns
with (1 - carry).  There is no good way to do that in combine, we would
need to combine three insns, the first two of which are a parallel.


  parent reply	other threads:[~2015-01-18 22:54 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 [this message]
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
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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