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* [Bug tree-optimization/94834] New: Failure to optimize loop bswap pattern
@ 2020-04-28 22:35 gabravier at gmail dot com
2020-04-29 7:08 ` [Bug tree-optimization/94834] " rguenth at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: gabravier at gmail dot com @ 2020-04-28 22:35 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94834
Bug ID: 94834
Summary: Failure to optimize loop bswap pattern
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: ---
uint32_t load(const uint8_t* data)
{
uint32_t val = 0;
for (int i = 0; i < sizeof(val) * CHAR_BIT; i += CHAR_BIT)
{
val |= *data++ << i;
}
return val;
}
This can be optimized to a single 32-bit load. LLVM does this transformation,
gcc just unrolls the loop and misses the transformation.
LLVM gives :
load(unsigned char const*): # @load(unsigned char const*)
mov eax, dword ptr [rdi]
ret
GCC gives :
load(unsigned char const*):
movzx edx, BYTE PTR [rdi+1]
movzx eax, BYTE PTR [rdi]
sal edx, 8
or edx, eax
movzx eax, BYTE PTR [rdi+2]
sal eax, 16
or edx, eax
movzx eax, BYTE PTR [rdi+3]
sal eax, 24
or eax, edx
ret
See also https://godbolt.org/z/kmYTLZ
^ permalink raw reply [flat|nested] 4+ messages in thread* [Bug tree-optimization/94834] Failure to optimize loop bswap pattern 2020-04-28 22:35 [Bug tree-optimization/94834] New: Failure to optimize loop bswap pattern gabravier at gmail dot com @ 2020-04-29 7:08 ` rguenth at gcc dot gnu.org 2020-04-29 9:40 ` gabravier at gmail dot com 2021-09-04 21:33 ` pinskia at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: rguenth at gcc dot gnu.org @ 2020-04-29 7:08 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94834 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Keywords| |missed-optimization Last reconfirmed| |2020-04-29 Ever confirmed|0 |1 --- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> --- Confirmed. We have a pass that would grok the unrolled form but unrolling happens too late (if at all) for it to trigger. Not sure if we should try to pattern-match this (or other reductions) in loop distribution. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/94834] Failure to optimize loop bswap pattern 2020-04-28 22:35 [Bug tree-optimization/94834] New: Failure to optimize loop bswap pattern gabravier at gmail dot com 2020-04-29 7:08 ` [Bug tree-optimization/94834] " rguenth at gcc dot gnu.org @ 2020-04-29 9:40 ` gabravier at gmail dot com 2021-09-04 21:33 ` pinskia at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: gabravier at gmail dot com @ 2020-04-29 9:40 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94834 --- Comment #2 from Gabriel Ravier <gabravier at gmail dot com> --- Now I wonder why the unrolling happens too late since there was 1 ecp check that should happen after the unrolling, from my understanding. Are the multiple ecp passes detecting different things? ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/94834] Failure to optimize loop bswap pattern 2020-04-28 22:35 [Bug tree-optimization/94834] New: Failure to optimize loop bswap pattern gabravier at gmail dot com 2020-04-29 7:08 ` [Bug tree-optimization/94834] " rguenth at gcc dot gnu.org 2020-04-29 9:40 ` gabravier at gmail dot com @ 2021-09-04 21:33 ` pinskia at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu.org @ 2021-09-04 21:33 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94834 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Resolution|--- |DUPLICATE Status|NEW |RESOLVED --- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> --- This is a dup of bug 89811. *** This bug has been marked as a duplicate of bug 89811 *** ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2021-09-04 21:33 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2020-04-28 22:35 [Bug tree-optimization/94834] New: Failure to optimize loop bswap pattern gabravier at gmail dot com 2020-04-29 7:08 ` [Bug tree-optimization/94834] " rguenth at gcc dot gnu.org 2020-04-29 9:40 ` gabravier at gmail dot com 2021-09-04 21:33 ` pinskia at gcc dot gnu.org
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