public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
* [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
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).