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* [Bug tree-optimization/116316] New: incorrect code with -O2 @ 2024-08-09 18:42 qinzhao at gcc dot gnu.org 2024-08-09 18:51 ` [Bug tree-optimization/116316] " pinskia at gcc dot gnu.org 2024-08-09 19:15 ` qinzhao at gcc dot gnu.org 0 siblings, 2 replies; 3+ messages in thread From: qinzhao at gcc dot gnu.org @ 2024-08-09 18:42 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116316 Bug ID: 116316 Summary: incorrect code with -O2 Product: gcc Version: 15.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: qinzhao at gcc dot gnu.org Target Milestone: --- the following testing case failed on both x86 and aarch64 with -O2, but passed with -O1: #include <stdio.h> struct annotated { int b; int c[]; } *array_annotated; int main(int argc, char *argv[]) { size_t __size = sizeof(struct annotated) + sizeof(*array_annotated->c) * 10; array_annotated = (struct annotated *) __builtin_malloc(__size); __builtin_memset(array_annotated, 0, __size); if (&(array_annotated->b)) *(size_t *)(&(array_annotated->b)) = 10; if (array_annotated->b != 10) __builtin_abort (); printf("pass\n"); return 0; } adding -fno-tree-fre -fno-tree-pre -fno-code-hoisting cures the issue [opc@qinzhao-aarch64-ol8 ~]$ ./Install/latest-d/bin/gcc t.c -O2 [opc@qinzhao-aarch64-ol8 ~]$ ./a.out Aborted (core dumped) [opc@qinzhao-aarch64-ol8 ~]$ ./Install/latest-d/bin/gcc t.c -O2 -fno-tree-fre -fno-tree-pre -fno-code-hoisting [opc@qinzhao-aarch64-ol8 ~]$ ./a.out pass ^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug tree-optimization/116316] incorrect code with -O2 2024-08-09 18:42 [Bug tree-optimization/116316] New: incorrect code with -O2 qinzhao at gcc dot gnu.org @ 2024-08-09 18:51 ` pinskia at gcc dot gnu.org 2024-08-09 19:15 ` qinzhao at gcc dot gnu.org 1 sibling, 0 replies; 3+ messages in thread From: pinskia at gcc dot gnu.org @ 2024-08-09 18:51 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116316 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution|--- |INVALID --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- <source>:13:6: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing] 13 | *(size_t *)(&(array_annotated->b)) = 10; | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -fno-strict-aliasing fixes it. You access `array_annotated->b` via size_t (which is most likely `unsigned long`) and via int. Since long and int are distant types (and not signed versions of each other) they don't alias. ^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug tree-optimization/116316] incorrect code with -O2 2024-08-09 18:42 [Bug tree-optimization/116316] New: incorrect code with -O2 qinzhao at gcc dot gnu.org 2024-08-09 18:51 ` [Bug tree-optimization/116316] " pinskia at gcc dot gnu.org @ 2024-08-09 19:15 ` qinzhao at gcc dot gnu.org 1 sibling, 0 replies; 3+ messages in thread From: qinzhao at gcc dot gnu.org @ 2024-08-09 19:15 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116316 --- Comment #2 from qinzhao at gcc dot gnu.org --- (In reply to Andrew Pinski from comment #1) > <source>:13:6: warning: dereferencing type-punned pointer will break > strict-aliasing rules [-Wstrict-aliasing] > 13 | *(size_t *)(&(array_annotated->b)) = 10; > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > -fno-strict-aliasing fixes it. > > You access `array_annotated->b` via size_t (which is most likely `unsigned > long`) and via int. Since long and int are distant types (and not signed > versions of each other) they don't alias. Okay, I see. thanks a lot. I did suspect that this is a source code issue, now confirmed. -:) ^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2024-08-09 19:15 UTC | newest] Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2024-08-09 18:42 [Bug tree-optimization/116316] New: incorrect code with -O2 qinzhao at gcc dot gnu.org 2024-08-09 18:51 ` [Bug tree-optimization/116316] " pinskia at gcc dot gnu.org 2024-08-09 19:15 ` qinzhao at gcc dot gnu.org
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