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* [Bug target/110457] New: Unnecessary movsx eax, dil
@ 2023-06-28 15:05 antoshkka at gmail dot com
2023-06-28 15:07 ` [Bug target/110457] " antoshkka at gmail dot com
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: antoshkka at gmail dot com @ 2023-06-28 15:05 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110457
Bug ID: 110457
Summary: Unnecessary movsx eax, dil
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: antoshkka at gmail dot com
Target Milestone: ---
For the following code
int sample1(char c) {
return (c << 4) + (c << 8) + (c << 16) + c;
}
GCC-14 with -O2 generates the assembly:
sample1(char):
movsx eax,dil
imul eax,eax,0x10111
ret
However, it could be shortened to just:
sample1(char):
imul eax,edi,0x10111
Godbolt playground: https://godbolt.org/z/7GGdedEY8
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug target/110457] Unnecessary movsx eax, dil
2023-06-28 15:05 [Bug target/110457] New: Unnecessary movsx eax, dil antoshkka at gmail dot com
@ 2023-06-28 15:07 ` antoshkka at gmail dot com
2023-06-28 15:58 ` pinskia at gcc dot gnu.org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: antoshkka at gmail dot com @ 2023-06-28 15:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110457
--- Comment #1 from Antony Polukhin <antoshkka at gmail dot com> ---
> However, it could be shortened to just:
sample1(char):
imul eax,edi,0x10111
ret ; missed in previous message
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug target/110457] Unnecessary movsx eax, dil
2023-06-28 15:05 [Bug target/110457] New: Unnecessary movsx eax, dil antoshkka at gmail dot com
2023-06-28 15:07 ` [Bug target/110457] " antoshkka at gmail dot com
@ 2023-06-28 15:58 ` pinskia at gcc dot gnu.org
2023-06-28 15:59 ` pinskia at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-06-28 15:58 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110457
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |ABI
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Why do you think that?
Iirc the x86_64 abi says the upper bits are undefined.
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug target/110457] Unnecessary movsx eax, dil
2023-06-28 15:05 [Bug target/110457] New: Unnecessary movsx eax, dil antoshkka at gmail dot com
2023-06-28 15:07 ` [Bug target/110457] " antoshkka at gmail dot com
2023-06-28 15:58 ` pinskia at gcc dot gnu.org
@ 2023-06-28 15:59 ` pinskia at gcc dot gnu.org
2023-06-28 16:29 ` antoshkka at gmail dot com
2023-06-29 12:10 ` xry111 at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-06-28 15:59 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110457
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target| |X86_64
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note iirc there is still a disagreement in what the abi says. Llvm folks says
it says one thing while gcc folks have said it says it undefined.
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug target/110457] Unnecessary movsx eax, dil
2023-06-28 15:05 [Bug target/110457] New: Unnecessary movsx eax, dil antoshkka at gmail dot com
` (2 preceding siblings ...)
2023-06-28 15:59 ` pinskia at gcc dot gnu.org
@ 2023-06-28 16:29 ` antoshkka at gmail dot com
2023-06-29 12:10 ` xry111 at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: antoshkka at gmail dot com @ 2023-06-28 16:29 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110457
--- Comment #4 from Antony Polukhin <antoshkka at gmail dot com> ---
Oh, if there's an disagreement I'm fine with closing this issue as
invalid/later/won't_fix
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug target/110457] Unnecessary movsx eax, dil
2023-06-28 15:05 [Bug target/110457] New: Unnecessary movsx eax, dil antoshkka at gmail dot com
` (3 preceding siblings ...)
2023-06-28 16:29 ` antoshkka at gmail dot com
@ 2023-06-29 12:10 ` xry111 at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: xry111 at gcc dot gnu.org @ 2023-06-29 12:10 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110457
Xi Ruoyao <xry111 at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
CC| |xry111 at gcc dot gnu.org
Status|UNCONFIRMED |WAITING
Last reconfirmed| |2023-06-29
--- Comment #5 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
I guess we need an ABI expert to clarify things.
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2023-06-29 12:10 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2023-06-28 15:05 [Bug target/110457] New: Unnecessary movsx eax, dil antoshkka at gmail dot com
2023-06-28 15:07 ` [Bug target/110457] " antoshkka at gmail dot com
2023-06-28 15:58 ` pinskia at gcc dot gnu.org
2023-06-28 15:59 ` pinskia at gcc dot gnu.org
2023-06-28 16:29 ` antoshkka at gmail dot com
2023-06-29 12:10 ` xry111 at gcc dot gnu.org
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