public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
* [Bug c/96317] New: [8/9/10/11] Int compare optimizations make some errors @ 2020-07-25 9:13 570070308 at qq dot com 2020-07-25 9:17 ` [Bug c/96317] " pinskia at gcc dot gnu.org ` (2 more replies) 0 siblings, 3 replies; 4+ messages in thread From: 570070308 at qq dot com @ 2020-07-25 9:13 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96317 Bug ID: 96317 Summary: [8/9/10/11] Int compare optimizations make some errors Product: gcc Version: 11.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: 570070308 at qq dot com Target Milestone: --- for the code: signed int a=2147483647; if( (signed int)( (signed int)a + (signed int)1 ) < (signed int)2147483647 ) { printf("111\n"); } if( (signed int)( (signed int)a + (signed int)1 ) < (signed int)2147483646 ) { printf("222\n"); } signed int b=2147483646; if( (signed int)( (signed int)a + (signed int)1 ) < (signed int)b ) { printf("333\n"); } The result is: 111 333 I have checked the assembly files. It seems that the compiler optimize the a+1<2147483646 to a<=2147483644. There are some other similar situations in compartion of <=,>,>=. I think it is better to change the ways or give out a warning. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c/96317] [8/9/10/11] Int compare optimizations make some errors 2020-07-25 9:13 [Bug c/96317] New: [8/9/10/11] Int compare optimizations make some errors 570070308 at qq dot com @ 2020-07-25 9:17 ` pinskia at gcc dot gnu.org 2020-07-25 9:18 ` pinskia at gcc dot gnu.org 2020-07-26 19:03 ` marxin at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu.org @ 2020-07-25 9:17 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96317 --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Use -fwrapv or unsigned integers as signed signed integer overflow is undefined. Use -fsanitizer=undefined will detect this at runtime. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c/96317] [8/9/10/11] Int compare optimizations make some errors 2020-07-25 9:13 [Bug c/96317] New: [8/9/10/11] Int compare optimizations make some errors 570070308 at qq dot com 2020-07-25 9:17 ` [Bug c/96317] " pinskia at gcc dot gnu.org @ 2020-07-25 9:18 ` pinskia at gcc dot gnu.org 2020-07-26 19:03 ` marxin at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu.org @ 2020-07-25 9:18 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96317 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Resolution|--- |INVALID Status|UNCONFIRMED |RESOLVED --- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> --- . ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c/96317] [8/9/10/11] Int compare optimizations make some errors 2020-07-25 9:13 [Bug c/96317] New: [8/9/10/11] Int compare optimizations make some errors 570070308 at qq dot com 2020-07-25 9:17 ` [Bug c/96317] " pinskia at gcc dot gnu.org 2020-07-25 9:18 ` pinskia at gcc dot gnu.org @ 2020-07-26 19:03 ` marxin at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: marxin at gcc dot gnu.org @ 2020-07-26 19:03 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96317 Martin Liška <marxin at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |marxin at gcc dot gnu.org --- Comment #3 from Martin Liška <marxin at gcc dot gnu.org> --- Or you can use UBSAN to see that: $ gcc pr96317.c -fsanitize=undefined && ./a.out pr96317.c:7:9: runtime error: signed integer overflow: 2147483647 + 1 cannot be represented in type 'int' 111 pr96317.c:18:9: runtime error: signed integer overflow: 2147483647 + 1 cannot be represented in type 'int' 333 ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2020-07-26 19:03 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2020-07-25 9:13 [Bug c/96317] New: [8/9/10/11] Int compare optimizations make some errors 570070308 at qq dot com 2020-07-25 9:17 ` [Bug c/96317] " pinskia at gcc dot gnu.org 2020-07-25 9:18 ` pinskia at gcc dot gnu.org 2020-07-26 19:03 ` marxin 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).