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* [Bug c/101705] New: Missed optimization opportunity when copying lots of bitfields
@ 2021-07-31 13:25 jengelh at inai dot de
2021-07-31 13:25 ` [Bug c/101705] " jengelh at inai dot de
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: jengelh at inai dot de @ 2021-07-31 13:25 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101705
Bug ID: 101705
Summary: Missed optimization opportunity when copying lots of
bitfields
Product: gcc
Version: 11.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: jengelh at inai dot de
Target Milestone: ---
Using gcc-11.1.1 [revision 62bbb113ae68a7e724255e17143520735bcb9ec9], I observe
that gcc is able to recognize and combine lots of "structb->member =
structa->member" assignments into SIMD instructions. However, this only works
as long as "member" has exactly 8*n bits. It would appear gcc is not smart
enough to consider smaller entities (if and when they add up to multiples of 8
or 64).
Observed
========
[On x86_64]
»gcc -O3 -c 1.c; gcc -O3 -c 2.c
»objdump -d 1.o
0: f3 0f 6f 3e movdqu (%rsi),%xmm7
...
»objdump -d 2.o
0: 0f b6 16 movzbl (%rsi),%edx
3: 0f b6 07 movzbl (%rdi),%eax
6: 83 e2 01 and $0x1,%edx
9: 83 e0 fe and $0xfffffffe,%eax
c: 09 d0 or %edx,%eax
e: 88 07 mov %al,(%rdi)
10: 0f b6 16 movzbl (%rsi),%edx
13: 83 e0 fd and $0xfffffffd,%eax
16: 83 e2 02 and $0x2,%edx
19: 09 d0 or %edx,%eax
1b: 88 07 mov %al,(%rdi)
...
Expected
========
Emit some movdqu/movups even for 2.c.
Other info
==========
gcc version 11.1.1 20210625 [revision 62bbb113ae68a7e724255e17143520735bcb9ec9]
(SUSE Linux) &
gcc version 7.5.0 (SUSE Linux)
^ permalink raw reply [flat|nested] 5+ messages in thread* [Bug c/101705] Missed optimization opportunity when copying lots of bitfields 2021-07-31 13:25 [Bug c/101705] New: Missed optimization opportunity when copying lots of bitfields jengelh at inai dot de @ 2021-07-31 13:25 ` jengelh at inai dot de 2021-07-31 13:25 ` jengelh at inai dot de ` (2 subsequent siblings) 3 siblings, 0 replies; 5+ messages in thread From: jengelh at inai dot de @ 2021-07-31 13:25 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101705 --- Comment #1 from Jan Engelhardt <jengelh at inai dot de> --- Created attachment 51228 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51228&action=edit testcase, 1.c ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c/101705] Missed optimization opportunity when copying lots of bitfields 2021-07-31 13:25 [Bug c/101705] New: Missed optimization opportunity when copying lots of bitfields jengelh at inai dot de 2021-07-31 13:25 ` [Bug c/101705] " jengelh at inai dot de @ 2021-07-31 13:25 ` jengelh at inai dot de 2021-07-31 19:35 ` [Bug tree-optimization/101705] " pinskia at gcc dot gnu.org 2021-08-02 8:38 ` rguenth at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: jengelh at inai dot de @ 2021-07-31 13:25 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101705 --- Comment #2 from Jan Engelhardt <jengelh at inai dot de> --- Created attachment 51229 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51229&action=edit testcase, 2.c ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/101705] Missed optimization opportunity when copying lots of bitfields 2021-07-31 13:25 [Bug c/101705] New: Missed optimization opportunity when copying lots of bitfields jengelh at inai dot de 2021-07-31 13:25 ` [Bug c/101705] " jengelh at inai dot de 2021-07-31 13:25 ` jengelh at inai dot de @ 2021-07-31 19:35 ` pinskia at gcc dot gnu.org 2021-08-02 8:38 ` rguenth at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2021-07-31 19:35 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101705 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Last reconfirmed| |2021-07-31 Status|UNCONFIRMED |ASSIGNED Keywords| |missed-optimization Ever confirmed|0 |1 Component|c |tree-optimization Assignee|unassigned at gcc dot gnu.org |pinskia at gcc dot gnu.org --- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Mine but for GCC 13. There are other bugs which say the same thing too. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/101705] Missed optimization opportunity when copying lots of bitfields 2021-07-31 13:25 [Bug c/101705] New: Missed optimization opportunity when copying lots of bitfields jengelh at inai dot de ` (2 preceding siblings ...) 2021-07-31 19:35 ` [Bug tree-optimization/101705] " pinskia at gcc dot gnu.org @ 2021-08-02 8:38 ` rguenth at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: rguenth at gcc dot gnu.org @ 2021-08-02 8:38 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101705 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Blocks| |53947 --- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> --- SLP vectorization handles this and it even splits the groups and would use smaller groups for the tail but then it fails: t.i:244:10: note: === vect_slp_analyze_instance_alignment === t.i:244:10: missed: desired vector type conflicts with earlier one for _113 = s_129(D)->b113; t.i:244:10: note: removing SLP instance operations starting from: d_130(D)->b113 = _113; t.i:252:10: note: === vect_slp_analyze_instance_alignment === t.i:252:10: missed: desired vector type conflicts with earlier one for _121 = s_129(D)->b121; t.i:252:10: note: removing SLP instance operations starting from: d_130(D)->b121 = _121; t.i:256:10: note: === vect_slp_analyze_instance_alignment === t.i:256:10: missed: desired vector type conflicts with earlier one for _125 = s_129(D)->b125; t.i:256:10: note: removing SLP instance operations starting from: d_130(D)->b125 = _125; which is a pre-existing issue (and I think there's a duplicate for the vectorizer issue). Not sure what part Andrew wants to look at. Without vectorization we don't merge anything. Referenced Bugs: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53947 [Bug 53947] [meta-bug] vectorizer missed-optimizations ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2021-08-02 8:38 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-07-31 13:25 [Bug c/101705] New: Missed optimization opportunity when copying lots of bitfields jengelh at inai dot de 2021-07-31 13:25 ` [Bug c/101705] " jengelh at inai dot de 2021-07-31 13:25 ` jengelh at inai dot de 2021-07-31 19:35 ` [Bug tree-optimization/101705] " pinskia at gcc dot gnu.org 2021-08-02 8:38 ` rguenth at gcc dot gnu.org
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