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* [Bug tree-optimization/113487] New: Missed optimization:simplify demanded bits on multi-use instructions like select
@ 2024-01-18 17:34 xxs_chy at outlook dot com
2024-01-18 17:35 ` [Bug tree-optimization/113487] " pinskia at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: xxs_chy at outlook dot com @ 2024-01-18 17:34 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113487
Bug ID: 113487
Summary: Missed optimization:simplify demanded bits on
multi-use instructions like select
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: xxs_chy at outlook dot com
Target Milestone: ---
Godbolt example: https://godbolt.org/z/EfKrTbK77
Based on common demanded bits from s&8 and s&16,
```
void src(bool c, unsigned a, unsigned b) {
unsigned s = c ? a & 24 : b & 25;
use(s & 8);
use(s & 16);
}
```
can be folded to:
```
void tgt(bool c, unsigned a, unsigned b) {
unsigned s = c ? a : b ;
use(s & 8);
use(s & 16);
}
```
Both LLVM and GCC missed this optimization opportunity.
^ permalink raw reply [flat|nested] 5+ messages in thread* [Bug tree-optimization/113487] Missed optimization:simplify demanded bits on multi-use instructions like select 2024-01-18 17:34 [Bug tree-optimization/113487] New: Missed optimization:simplify demanded bits on multi-use instructions like select xxs_chy at outlook dot com @ 2024-01-18 17:35 ` pinskia at gcc dot gnu.org 2024-01-18 17:38 ` pinskia at gcc dot gnu.org ` (2 subsequent siblings) 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2024-01-18 17:35 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113487 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Keywords| |missed-optimization Severity|normal |enhancement ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/113487] Missed optimization:simplify demanded bits on multi-use instructions like select 2024-01-18 17:34 [Bug tree-optimization/113487] New: Missed optimization:simplify demanded bits on multi-use instructions like select xxs_chy at outlook dot com 2024-01-18 17:35 ` [Bug tree-optimization/113487] " pinskia at gcc dot gnu.org @ 2024-01-18 17:38 ` pinskia at gcc dot gnu.org 2024-01-18 17:41 ` xxs_chy at outlook dot com 2024-01-19 7:14 ` rguenth at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2024-01-18 17:38 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113487 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Last reconfirmed| |2024-01-18 Status|UNCONFIRMED |NEW Ever confirmed|0 |1 --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Confirmed. I don't know which pass this would be best implemented in though. Maybe phiopt but I am not 100% sure there ... ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/113487] Missed optimization:simplify demanded bits on multi-use instructions like select 2024-01-18 17:34 [Bug tree-optimization/113487] New: Missed optimization:simplify demanded bits on multi-use instructions like select xxs_chy at outlook dot com 2024-01-18 17:35 ` [Bug tree-optimization/113487] " pinskia at gcc dot gnu.org 2024-01-18 17:38 ` pinskia at gcc dot gnu.org @ 2024-01-18 17:41 ` xxs_chy at outlook dot com 2024-01-19 7:14 ` rguenth at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: xxs_chy at outlook dot com @ 2024-01-18 17:41 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113487 --- Comment #2 from XChy <xxs_chy at outlook dot com> --- I may miss something here... Apart from this one, it seems that GCC doesn't simplify **one-use** instruction based on demanded bits too: https://godbolt.org/z/67bYxd8hY But LLVM indeed handle the one-use case. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/113487] Missed optimization:simplify demanded bits on multi-use instructions like select 2024-01-18 17:34 [Bug tree-optimization/113487] New: Missed optimization:simplify demanded bits on multi-use instructions like select xxs_chy at outlook dot com ` (2 preceding siblings ...) 2024-01-18 17:41 ` xxs_chy at outlook dot com @ 2024-01-19 7:14 ` rguenth at gcc dot gnu.org 3 siblings, 0 replies; 5+ messages in thread From: rguenth at gcc dot gnu.org @ 2024-01-19 7:14 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113487 --- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> --- Feels more like reassoc to me. You could also view it as "bit-DCE", eliding defs of dead bits. Which might make it suitable for backprop (currently doing sth similar for the sign "bit"). ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2024-01-19 7:14 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2024-01-18 17:34 [Bug tree-optimization/113487] New: Missed optimization:simplify demanded bits on multi-use instructions like select xxs_chy at outlook dot com 2024-01-18 17:35 ` [Bug tree-optimization/113487] " pinskia at gcc dot gnu.org 2024-01-18 17:38 ` pinskia at gcc dot gnu.org 2024-01-18 17:41 ` xxs_chy at outlook dot com 2024-01-19 7:14 ` rguenth at gcc dot gnu.org
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