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* [Bug rtl-optimization/109845] New: Addition overflow/carry flag unnecessarily put in a temporary register @ 2023-05-13 18:32 chfast at gmail dot com 2023-05-13 18:39 ` [Bug rtl-optimization/109845] " pinskia at gcc dot gnu.org ` (2 more replies) 0 siblings, 3 replies; 4+ messages in thread From: chfast at gmail dot com @ 2023-05-13 18:32 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109845 Bug ID: 109845 Summary: Addition overflow/carry flag unnecessarily put in a temporary register Product: gcc Version: 13.1.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: rtl-optimization Assignee: unassigned at gcc dot gnu.org Reporter: chfast at gmail dot com Target Milestone: --- When we have an addition and an overflow check and the overflow flag is combined with some other condition the codegen may generate variant when the overflow flag is temporary register. unsigned s = y + z; _Bool ov = s < y; if (x || ov) return; This produces add esi, edx setc al test edi, edi jne .L1 test eax, eax jne .L1 while it could be add esi, edx jc .L6 test edi, edi jne .L6 There are easy workaround to the C code which make the assembly optimal: 1. Change the order of checks if (ov || x) 2. Split if into two if (x) return; if (ov) return; https://godbolt.org/z/rxsrnhPdc ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug rtl-optimization/109845] Addition overflow/carry flag unnecessarily put in a temporary register 2023-05-13 18:32 [Bug rtl-optimization/109845] New: Addition overflow/carry flag unnecessarily put in a temporary register chfast at gmail dot com @ 2023-05-13 18:39 ` pinskia at gcc dot gnu.org 2023-05-13 18:45 ` [Bug middle-end/109845] " pinskia at gcc dot gnu.org 2023-05-15 6:52 ` rguenth at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu.org @ 2023-05-13 18:39 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109845 --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Created attachment 55077 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55077&action=edit full testcase Next time please attach the full compilable testcase or paste it inline rather than just including a godbolt link. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug middle-end/109845] Addition overflow/carry flag unnecessarily put in a temporary register 2023-05-13 18:32 [Bug rtl-optimization/109845] New: Addition overflow/carry flag unnecessarily put in a temporary register chfast at gmail dot com 2023-05-13 18:39 ` [Bug rtl-optimization/109845] " pinskia at gcc dot gnu.org @ 2023-05-13 18:45 ` pinskia at gcc dot gnu.org 2023-05-15 6:52 ` rguenth at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu.org @ 2023-05-13 18:45 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109845 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Last reconfirmed| |2023-05-13 Status|UNCONFIRMED |NEW Severity|normal |enhancement Component|rtl-optimization |middle-end Keywords| |missed-optimization Ever confirmed|0 |1 --- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> --- So the difference between good1 and bad1 at the gimple level is the order of operands of the bit_ior: good1: ov_8 = _13 != 0; _9 = x_2(D) != 0; _10 = ov_8 | _9; if (_10 != 0) bad1: ov_7 = _13 != 0; _1 = x_8(D) != 0; _2 = _1 | ov_7; if (_2 != 0) ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug middle-end/109845] Addition overflow/carry flag unnecessarily put in a temporary register 2023-05-13 18:32 [Bug rtl-optimization/109845] New: Addition overflow/carry flag unnecessarily put in a temporary register chfast at gmail dot com 2023-05-13 18:39 ` [Bug rtl-optimization/109845] " pinskia at gcc dot gnu.org 2023-05-13 18:45 ` [Bug middle-end/109845] " pinskia at gcc dot gnu.org @ 2023-05-15 6:52 ` rguenth at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: rguenth at gcc dot gnu.org @ 2023-05-15 6:52 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109845 --- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> --- Yup, bad luck for later RTL optimization. It might help to perform jump expansions decision to go for jump or straight-line code earlier on GIMPLE (and stick to that). ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2023-05-15 6:52 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2023-05-13 18:32 [Bug rtl-optimization/109845] New: Addition overflow/carry flag unnecessarily put in a temporary register chfast at gmail dot com 2023-05-13 18:39 ` [Bug rtl-optimization/109845] " pinskia at gcc dot gnu.org 2023-05-13 18:45 ` [Bug middle-end/109845] " pinskia at gcc dot gnu.org 2023-05-15 6:52 ` rguenth at gcc dot gnu.org
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