public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
* [Bug ada/46943] New: Unnecessary ZERO_EXTEND @ 2010-12-14 17:34 jakub at gcc dot gnu.org 2010-12-16 15:10 ` [Bug rtl-optimization/46943] " rguenth at gcc dot gnu.org ` (2 more replies) 0 siblings, 3 replies; 4+ messages in thread From: jakub at gcc dot gnu.org @ 2010-12-14 17:34 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46943 Summary: Unnecessary ZERO_EXTEND Product: gcc Version: 4.6.0 Status: UNCONFIRMED Keywords: missed-optimization Severity: normal Priority: P3 Component: ada AssignedTo: unassigned@gcc.gnu.org ReportedBy: jakub@gcc.gnu.org Target: x86_64-linux In http://blog.regehr.org/archives/320 Example 4 unsigned long long v; unsigned short foo (signed char x, unsigned short y) { v = (unsigned long long) y; return (unsigned short) ((int) y / 3); } we emit a redundant zero-extension: movzwl %si, %eax movq %rax, v(%rip) movzwl %si, %eax imull $43691, %eax, %eax shrl $17, %eax ret The reason why the second movzwl %si, %eax wasn't CSEd with the first one is because the first one is (set (reg:DI reg1) (zero_extend:DI (reg:HI reg2)) while the second one is (set (reg:SI reg3) (zero_extend:SI (reg:HI reg2)) Wonder if we can't teach CSE to optimize it (say that reg3 is actually (subreg:SI (reg:DI reg1) 0), or if e.g. one of the zee/see passes (implicit-zee e.g.) couldn't handle such cases. Combiner can't do anything here, as there is no data dependency, so try_combine won't see them together. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug rtl-optimization/46943] Unnecessary ZERO_EXTEND 2010-12-14 17:34 [Bug ada/46943] New: Unnecessary ZERO_EXTEND jakub at gcc dot gnu.org @ 2010-12-16 15:10 ` rguenth at gcc dot gnu.org 2012-02-02 8:52 ` pinskia at gcc dot gnu.org 2023-05-20 1:57 ` pinskia at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: rguenth at gcc dot gnu.org @ 2010-12-16 15:10 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46943 --- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2010-12-16 15:10:12 UTC --- Hmm. I think at least postreload CSE should handle it as we then know that zero-extends extend to the full HW register. Pre-regalloc would be difficult as we'd need some new form of canonicalization with an associated cost (think of a zero_extend:TI). ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug rtl-optimization/46943] Unnecessary ZERO_EXTEND 2010-12-14 17:34 [Bug ada/46943] New: Unnecessary ZERO_EXTEND jakub at gcc dot gnu.org 2010-12-16 15:10 ` [Bug rtl-optimization/46943] " rguenth at gcc dot gnu.org @ 2012-02-02 8:52 ` pinskia at gcc dot gnu.org 2023-05-20 1:57 ` pinskia at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu.org @ 2012-02-02 8:52 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46943 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Last reconfirmed| |2012-02-02 Ever Confirmed|0 |1 --- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-02-02 08:51:50 UTC --- Confirmed. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug rtl-optimization/46943] Unnecessary ZERO_EXTEND 2010-12-14 17:34 [Bug ada/46943] New: Unnecessary ZERO_EXTEND jakub at gcc dot gnu.org 2010-12-16 15:10 ` [Bug rtl-optimization/46943] " rguenth at gcc dot gnu.org 2012-02-02 8:52 ` pinskia at gcc dot gnu.org @ 2023-05-20 1:57 ` pinskia at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu.org @ 2023-05-20 1:57 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=46943 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Last reconfirmed|2018-04-22 00:00:00 |2023-5-19 Severity|normal |enhancement ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2023-05-20 1:57 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2010-12-14 17:34 [Bug ada/46943] New: Unnecessary ZERO_EXTEND jakub at gcc dot gnu.org 2010-12-16 15:10 ` [Bug rtl-optimization/46943] " rguenth at gcc dot gnu.org 2012-02-02 8:52 ` pinskia at gcc dot gnu.org 2023-05-20 1:57 ` pinskia 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).