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* [Bug c/66663] New: gcc misses optimization emits useless test of (a & 31) with 32
@ 2015-06-25 12:02 fuz at fuz dot su
2015-06-25 12:14 ` [Bug c/66663] " fuz at fuz dot su
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: fuz at fuz dot su @ 2015-06-25 12:02 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66663
Bug ID: 66663
Summary: gcc misses optimization emits useless test of (a & 31)
with 32
Product: gcc
Version: 5.0
Status: UNCONFIRMED
Severity: minor
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: fuz at fuz dot su
Target Milestone: ---
The following code:
unsigned long long foo(unsigned long long x, int a) {
return x << (a & 31);
}
compiled with a recent build of gcc for i386 Linux (with -O3) yields the
following assembly:
foo:
movl 12(%esp), %ecx
movl 4(%esp), %eax
movl 8(%esp), %edx
andl $31, %ecx
shldl %eax, %edx
sall %cl, %eax
testb $32, %cl
je .L2
movl %eax, %edx
xorl %eax, %eax
.L2:
rep ret
.ident "GCC: (GNU) 5.0.0 20150314 (experimental)"
The testb instruction seems redundant as %cl has been masked with $31 a few
instructions before: The jump will never be taken.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c/66663] gcc misses optimization emits useless test of (a & 31) with 32
2015-06-25 12:02 [Bug c/66663] New: gcc misses optimization emits useless test of (a & 31) with 32 fuz at fuz dot su
@ 2015-06-25 12:14 ` fuz at fuz dot su
2021-07-27 0:01 ` [Bug target/66663] " pinskia at gcc dot gnu.org
2021-07-27 0:05 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: fuz at fuz dot su @ 2015-06-25 12:14 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66663
--- Comment #1 from Robert Clausecker <fuz at fuz dot su> ---
Sorry. I meant to say: The branch will always be taken, not never.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug target/66663] gcc misses optimization emits useless test of (a & 31) with 32
2015-06-25 12:02 [Bug c/66663] New: gcc misses optimization emits useless test of (a & 31) with 32 fuz at fuz dot su
2015-06-25 12:14 ` [Bug c/66663] " fuz at fuz dot su
@ 2021-07-27 0:01 ` pinskia at gcc dot gnu.org
2021-07-27 0:05 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-07-27 0:01 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66663
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Target Milestone|--- |9.0
Resolution|--- |FIXED
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
GCC 9+ is able to produce:
foo(unsigned long long, int):
.LFB0:
.cfi_startproc
movl 4(%esp), %eax
movl 12(%esp), %ecx
movl 8(%esp), %edx
shldl %eax, %edx
sall %cl, %eax
ret
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug target/66663] gcc misses optimization emits useless test of (a & 31) with 32
2015-06-25 12:02 [Bug c/66663] New: gcc misses optimization emits useless test of (a & 31) with 32 fuz at fuz dot su
2015-06-25 12:14 ` [Bug c/66663] " fuz at fuz dot su
2021-07-27 0:01 ` [Bug target/66663] " pinskia at gcc dot gnu.org
@ 2021-07-27 0:05 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-07-27 0:05 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66663
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|FIXED |DUPLICATE
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
It was fixed by r9-62 which means this is a dup of bug 84431.
*** This bug has been marked as a duplicate of bug 84431 ***
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2021-07-27 0:05 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2015-06-25 12:02 [Bug c/66663] New: gcc misses optimization emits useless test of (a & 31) with 32 fuz at fuz dot su
2015-06-25 12:14 ` [Bug c/66663] " fuz at fuz dot su
2021-07-27 0:01 ` [Bug target/66663] " pinskia at gcc dot gnu.org
2021-07-27 0:05 ` pinskia at gcc dot gnu.org
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