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* [Bug c/103647] New: constant array comparison not always folded @ 2021-12-10 11:01 denis.campredon at gmail dot com 2021-12-10 20:29 ` [Bug tree-optimization/103647] " pinskia at gcc dot gnu.org ` (2 more replies) 0 siblings, 3 replies; 4+ messages in thread From: denis.campredon at gmail dot com @ 2021-12-10 11:01 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103647 Bug ID: 103647 Summary: constant array comparison not always folded Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: denis.campredon at gmail dot com Target Milestone: --- On trunk and gcc 11, with -O2 the following functions are not optimized to xor eax, eax ------------ bool f() { char a[] = {'a', 'c'}; char b[] = {'a', 'b'}; return __builtin_memcmp(a, b, 2); } bool g() { char a[] = {'a', 'b'}; char b[] = {'a', 'b', 'c'}; return __builtin_memcmp(a, b, 2); } ------------ .LC1: .string "ab" .LC0: .string "ac" f(): movzx eax, WORD PTR .LC1[rip] cmp WORD PTR .LC0[rip], ax setne al ret g(): cmp WORD PTR .LC1[rip], 25185 setne al ret ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/103647] constant array comparison not always folded 2021-12-10 11:01 [Bug c/103647] New: constant array comparison not always folded denis.campredon at gmail dot com @ 2021-12-10 20:29 ` pinskia at gcc dot gnu.org 2021-12-10 20:31 ` pinskia at gcc dot gnu.org 2022-01-04 9:24 ` rguenth at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu.org @ 2021-12-10 20:29 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103647 --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- well f should be optimized to return true while g should be optimized to return false. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/103647] constant array comparison not always folded 2021-12-10 11:01 [Bug c/103647] New: constant array comparison not always folded denis.campredon at gmail dot com 2021-12-10 20:29 ` [Bug tree-optimization/103647] " pinskia at gcc dot gnu.org @ 2021-12-10 20:31 ` pinskia at gcc dot gnu.org 2022-01-04 9:24 ` rguenth at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu.org @ 2021-12-10 20:31 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103647 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Last reconfirmed| |2021-12-10 Severity|normal |enhancement Ever confirmed|0 |1 --- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> --- So in fab GCC creates: a = "ac"; b = "ab"; _8 = MEM <unsigned short> [(char * {ref-all})&a]; _9 = MEM <unsigned short> [(char * {ref-all})&b]; _10 = _8 != _9; And: a = "ab"; b = "abc"; _8 = MEM <unsigned short> [(char * {ref-all})&a]; _9 = MEM <unsigned short> [(char * {ref-all})&b]; _10 = _8 != _9; But we don't have a FRE/DOM to optimize those MEM_REFs. Confirmed. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/103647] constant array comparison not always folded 2021-12-10 11:01 [Bug c/103647] New: constant array comparison not always folded denis.campredon at gmail dot com 2021-12-10 20:29 ` [Bug tree-optimization/103647] " pinskia at gcc dot gnu.org 2021-12-10 20:31 ` pinskia at gcc dot gnu.org @ 2022-01-04 9:24 ` rguenth at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: rguenth at gcc dot gnu.org @ 2022-01-04 9:24 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103647 --- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> --- fab is a bit late for this part of memcmp folding I guess, I'd have expected that to happen in generic folding like when we inline memcpy. It seems it's actually the strlen pass that inlines the compare. ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2022-01-04 9:24 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-12-10 11:01 [Bug c/103647] New: constant array comparison not always folded denis.campredon at gmail dot com 2021-12-10 20:29 ` [Bug tree-optimization/103647] " pinskia at gcc dot gnu.org 2021-12-10 20:31 ` pinskia at gcc dot gnu.org 2022-01-04 9:24 ` rguenth at gcc dot gnu.org
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