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* [Bug tree-optimization/94877] New: Failure to simplify ~(x + 1) to -2 - x
@ 2020-04-30 12:02 gabravier at gmail dot com
2020-04-30 12:50 ` [Bug tree-optimization/94877] " rguenth at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: gabravier at gmail dot com @ 2020-04-30 12:02 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94877
Bug ID: 94877
Summary: Failure to simplify ~(x + 1) to -2 - x
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: gabravier at gmail dot com
Target Milestone: ---
int f(int x)
{
return ~(x + 1);
}
With -O3, LLVM outputs this :
f(int): # @f(int)
mov eax, -2
sub eax, edi
ret
GCC outputs this :
f(int):
lea eax, [rdi+1]
not eax
ret
`~x - 1` is already simplified to `-2 - x`, so optimizing this looks like it
would make sense too.
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug tree-optimization/94877] Failure to simplify ~(x + 1) to -2 - x
2020-04-30 12:02 [Bug tree-optimization/94877] New: Failure to simplify ~(x + 1) to -2 - x gabravier at gmail dot com
@ 2020-04-30 12:50 ` rguenth at gcc dot gnu.org
2020-04-30 19:08 ` pinskia at gcc dot gnu.org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: rguenth at gcc dot gnu.org @ 2020-04-30 12:50 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94877
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2020-04-30
Keywords| |easyhack
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug tree-optimization/94877] Failure to simplify ~(x + 1) to -2 - x
2020-04-30 12:02 [Bug tree-optimization/94877] New: Failure to simplify ~(x + 1) to -2 - x gabravier at gmail dot com
2020-04-30 12:50 ` [Bug tree-optimization/94877] " rguenth at gcc dot gnu.org
@ 2020-04-30 19:08 ` pinskia at gcc dot gnu.org
2020-05-06 14:55 ` jakub at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2020-04-30 19:08 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94877
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Related to PR 23666.
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug tree-optimization/94877] Failure to simplify ~(x + 1) to -2 - x
2020-04-30 12:02 [Bug tree-optimization/94877] New: Failure to simplify ~(x + 1) to -2 - x gabravier at gmail dot com
2020-04-30 12:50 ` [Bug tree-optimization/94877] " rguenth at gcc dot gnu.org
2020-04-30 19:08 ` pinskia at gcc dot gnu.org
@ 2020-05-06 14:55 ` jakub at gcc dot gnu.org
2020-05-06 15:56 ` ubizjak at gmail dot com
2021-08-14 23:47 ` pinskia at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: jakub at gcc dot gnu.org @ 2020-05-06 14:55 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94877
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I'm not sure why this is considered a simplification, two insns vs. two, and on
the subtraction it isn't specific to just one target, but I think for most the
constant will need to be forced into register, the immediates the instructions
have is mostly for the second operand.
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug tree-optimization/94877] Failure to simplify ~(x + 1) to -2 - x
2020-04-30 12:02 [Bug tree-optimization/94877] New: Failure to simplify ~(x + 1) to -2 - x gabravier at gmail dot com
` (2 preceding siblings ...)
2020-05-06 14:55 ` jakub at gcc dot gnu.org
@ 2020-05-06 15:56 ` ubizjak at gmail dot com
2021-08-14 23:47 ` pinskia at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: ubizjak at gmail dot com @ 2020-05-06 15:56 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94877
--- Comment #4 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Jakub Jelinek from comment #3)
> I'm not sure why this is considered a simplification, two insns vs. two, and
> on the subtraction it isn't specific to just one target, but I think for
> most the constant will need to be forced into register, the immediates the
> instructions have is mostly for the second operand.
Two ALU operations are merged into one, assuming that move is "free".
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug tree-optimization/94877] Failure to simplify ~(x + 1) to -2 - x
2020-04-30 12:02 [Bug tree-optimization/94877] New: Failure to simplify ~(x + 1) to -2 - x gabravier at gmail dot com
` (3 preceding siblings ...)
2020-05-06 15:56 ` ubizjak at gmail dot com
@ 2021-08-14 23:47 ` pinskia at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-08-14 23:47 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94877
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Depends on| |96685
Target Milestone|--- |11.0
Status|NEW |RESOLVED
Resolution|--- |FIXED
--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Fixed in GCC 11+ by r11-5958 aka PR 96685.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96685
[Bug 96685] Failure to optimize not+sub to add+not
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2021-08-14 23:47 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2020-04-30 12:02 [Bug tree-optimization/94877] New: Failure to simplify ~(x + 1) to -2 - x gabravier at gmail dot com
2020-04-30 12:50 ` [Bug tree-optimization/94877] " rguenth at gcc dot gnu.org
2020-04-30 19:08 ` pinskia at gcc dot gnu.org
2020-05-06 14:55 ` jakub at gcc dot gnu.org
2020-05-06 15:56 ` ubizjak at gmail dot com
2021-08-14 23:47 ` pinskia at gcc dot gnu.org
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