public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
* [Bug target/102438] New: [x86-64] Failure to optimize out random extra store+load in vector code when memcpy is used
@ 2021-09-21 22:37 gabravier at gmail dot com
2021-09-21 23:32 ` [Bug target/102438] [x86-64] Failure to optimize out spill in vector code when a cast " pinskia at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: gabravier at gmail dot com @ 2021-09-21 22:37 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102438
Bug ID: 102438
Summary: [x86-64] Failure to optimize out random extra
store+load in vector code when memcpy is used
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: gabravier at gmail dot com
Target Milestone: ---
#include <stddef.h>
typedef double simde_float64x1_t __attribute__((__vector_size__(8)));
simde_float64x1_t simde_vabs_f64(simde_float64x1_t a) {
simde_float64x1_t r;
r[0] = -a[0];
return (simde_float64x1_t)r;
}
On AMD64 with -O3, this is outputted:
simde_vabs_f64(double __vector(1)):
movsd xmm0, QWORD PTR [rsp+8]
xorpd xmm0, XMMWORD PTR .LC0[rip]
mov rax, rdi
movsd QWORD PTR [rsp-24], xmm0
mov rdx, QWORD PTR [rsp-24]
mov QWORD PTR [rdi], rdx
ret
If we instead just return `r` (without the cast) this is instead outputted:
simde_vabs_f64(double __vector(1)):
movsd xmm0, QWORD PTR [rsp+8]
xorpd xmm0, XMMWORD PTR .LC0[rip]
mov rax, rdi
movsd QWORD PTR [rdi], xmm0
ret
It seems as though the presence of a cast (to the same type, no less) confuses
GCC into spilling the result into memory.
The GIMPLE optimized output is different for the two, so idk how much this
target-specific to x86, but I haven't been able to reproduce it anywhere else,
so ¯\_(ツ)_/¯.
PS: The same bug can also be reproduced with -m32
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug target/102438] [x86-64] Failure to optimize out spill in vector code when a cast is used
2021-09-21 22:37 [Bug target/102438] New: [x86-64] Failure to optimize out random extra store+load in vector code when memcpy is used gabravier at gmail dot com
@ 2021-09-21 23:32 ` pinskia at gcc dot gnu.org
2021-09-21 23:33 ` pinskia at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-09-21 23:32 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102438
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2021-09-21
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
Severity|normal |enhancement
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
There is an ABI difference between GCC and clang here ....
But I suspect this is the one of the standard return/argument issues with
respect to gcc.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug target/102438] [x86-64] Failure to optimize out spill in vector code when a cast is used
2021-09-21 22:37 [Bug target/102438] New: [x86-64] Failure to optimize out random extra store+load in vector code when memcpy is used gabravier at gmail dot com
2021-09-21 23:32 ` [Bug target/102438] [x86-64] Failure to optimize out spill in vector code when a cast " pinskia at gcc dot gnu.org
@ 2021-09-21 23:33 ` pinskia at gcc dot gnu.org
2021-09-22 3:04 ` crazylht at gmail dot com
2021-09-22 3:08 ` crazylht at gmail dot com
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-09-21 23:33 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102438
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
There might be a dup of this bug too.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug target/102438] [x86-64] Failure to optimize out spill in vector code when a cast is used
2021-09-21 22:37 [Bug target/102438] New: [x86-64] Failure to optimize out random extra store+load in vector code when memcpy is used gabravier at gmail dot com
2021-09-21 23:32 ` [Bug target/102438] [x86-64] Failure to optimize out spill in vector code when a cast " pinskia at gcc dot gnu.org
2021-09-21 23:33 ` pinskia at gcc dot gnu.org
@ 2021-09-22 3:04 ` crazylht at gmail dot com
2021-09-22 3:08 ` crazylht at gmail dot com
3 siblings, 0 replies; 5+ messages in thread
From: crazylht at gmail dot com @ 2021-09-22 3:04 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102438
--- Comment #3 from Hongtao.liu <crazylht at gmail dot com> ---
currently the i386 backend doesn't support V1DFmode, and it's treated as a
DImode (an equal-size integer type) and passed by stack.
Shall we support V1DFmode?
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug target/102438] [x86-64] Failure to optimize out spill in vector code when a cast is used
2021-09-21 22:37 [Bug target/102438] New: [x86-64] Failure to optimize out random extra store+load in vector code when memcpy is used gabravier at gmail dot com
` (2 preceding siblings ...)
2021-09-22 3:04 ` crazylht at gmail dot com
@ 2021-09-22 3:08 ` crazylht at gmail dot com
3 siblings, 0 replies; 5+ messages in thread
From: crazylht at gmail dot com @ 2021-09-22 3:08 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102438
--- Comment #4 from Hongtao.liu <crazylht at gmail dot com> ---
(In reply to Hongtao.liu from comment #3)
> currently the i386 backend doesn't support V1DFmode, and it's treated as a
> DImode (an equal-size integer type) and passed by stack.
typo, moved through stack.
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2021-09-22 3:08 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-09-21 22:37 [Bug target/102438] New: [x86-64] Failure to optimize out random extra store+load in vector code when memcpy is used gabravier at gmail dot com
2021-09-21 23:32 ` [Bug target/102438] [x86-64] Failure to optimize out spill in vector code when a cast " pinskia at gcc dot gnu.org
2021-09-21 23:33 ` pinskia at gcc dot gnu.org
2021-09-22 3:04 ` crazylht at gmail dot com
2021-09-22 3:08 ` crazylht at gmail dot com
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).