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* [Bug c++/102022] New: incorrect code with -O2 @ 2021-08-23 10:27 scu319hy at msn dot com 2021-08-23 10:30 ` [Bug c++/102022] " marxin at gcc dot gnu.org ` (4 more replies) 0 siblings, 5 replies; 6+ messages in thread From: scu319hy at msn dot com @ 2021-08-23 10:27 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102022 Bug ID: 102022 Summary: incorrect code with -O2 Product: gcc Version: 10.3.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: scu319hy at msn dot com Target Milestone: --- following code doesn't works well with -O2 flag. #include <stdio.h> #include <memory.h> #include <stdlib.h> struct _node_t { _node_t * _next; }; static void _rebase_ptr(char *&ptr, void *old_base, void *new_base) { if ( ptr != 0 ) { ptr = (char *)((char *)(ptr) - (char *)(old_base) + (char *)(new_base)); } } static void _rebase_ptr( _node_t *&head, void *old_base, void *new_base ) { _rebase_ptr(*(char**)&head, old_base, new_base); // error!! value of "head" not changed _node_t * node = head; while( node != 0 ) { _rebase_ptr( *(char**)&(node->_next), old_base, new_base ); node = node->_next; } } int main() { _node_t *tmp = (_node_t *)calloc(1, sizeof(_node_t)); _node_t *tmp2 = (_node_t *)calloc(1, sizeof(_node_t)); memcpy(tmp2, tmp, sizeof(_node_t)); free(tmp); _rebase_ptr(tmp, tmp, tmp2); printf("%llx == %llx\n", (long long)tmp, (long long)tmp2); free(tmp); return 0; } ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/102022] incorrect code with -O2 2021-08-23 10:27 [Bug c++/102022] New: incorrect code with -O2 scu319hy at msn dot com @ 2021-08-23 10:30 ` marxin at gcc dot gnu.org 2021-08-23 10:33 ` pinskia at gcc dot gnu.org ` (3 subsequent siblings) 4 siblings, 0 replies; 6+ messages in thread From: marxin at gcc dot gnu.org @ 2021-08-23 10:30 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102022 Martin Liška <marxin at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |hubicka at gcc dot gnu.org, | |marxin at gcc dot gnu.org Ever confirmed|0 |1 Last reconfirmed| |2021-08-23 Status|UNCONFIRMED |NEW --- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> --- Started with r6-1220-g6e042ef4e2b96c07. ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/102022] incorrect code with -O2 2021-08-23 10:27 [Bug c++/102022] New: incorrect code with -O2 scu319hy at msn dot com 2021-08-23 10:30 ` [Bug c++/102022] " marxin at gcc dot gnu.org @ 2021-08-23 10:33 ` pinskia at gcc dot gnu.org 2021-08-23 10:36 ` pinskia at gcc dot gnu.org ` (2 subsequent siblings) 4 siblings, 0 replies; 6+ messages in thread From: pinskia at gcc dot gnu.org @ 2021-08-23 10:33 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102022 --- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> --- This part of the code looks like there could be a huge alias violation waiting to happen *(char**)&head ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/102022] incorrect code with -O2 2021-08-23 10:27 [Bug c++/102022] New: incorrect code with -O2 scu319hy at msn dot com 2021-08-23 10:30 ` [Bug c++/102022] " marxin at gcc dot gnu.org 2021-08-23 10:33 ` pinskia at gcc dot gnu.org @ 2021-08-23 10:36 ` pinskia at gcc dot gnu.org 2021-08-23 13:22 ` rguenth at gcc dot gnu.org 2021-08-23 13:24 ` jakub at gcc dot gnu.org 4 siblings, 0 replies; 6+ messages in thread From: pinskia at gcc dot gnu.org @ 2021-08-23 10:36 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102022 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED Resolution|--- |INVALID --- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> --- And yes it is. You write head as both char* and then read it as head*. That is an alias violation for sure. Use either -fno-strict-aliasing go figure out a way to use an union or memcpy. ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/102022] incorrect code with -O2 2021-08-23 10:27 [Bug c++/102022] New: incorrect code with -O2 scu319hy at msn dot com ` (2 preceding siblings ...) 2021-08-23 10:36 ` pinskia at gcc dot gnu.org @ 2021-08-23 13:22 ` rguenth at gcc dot gnu.org 2021-08-23 13:24 ` jakub at gcc dot gnu.org 4 siblings, 0 replies; 6+ messages in thread From: rguenth at gcc dot gnu.org @ 2021-08-23 13:22 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102022 --- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> --- You could use *(void **) which GCC(!) treats conservative. But yes, *(char **)&head should use memcpy to be truly portable. ^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/102022] incorrect code with -O2 2021-08-23 10:27 [Bug c++/102022] New: incorrect code with -O2 scu319hy at msn dot com ` (3 preceding siblings ...) 2021-08-23 13:22 ` rguenth at gcc dot gnu.org @ 2021-08-23 13:24 ` jakub at gcc dot gnu.org 4 siblings, 0 replies; 6+ messages in thread From: jakub at gcc dot gnu.org @ 2021-08-23 13:24 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102022 Jakub Jelinek <jakub at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |jakub at gcc dot gnu.org --- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Or when you already use C++ change _rebase_ptr into a function template that will handle T *&ptr for template parameter T. ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2021-08-23 13:24 UTC | newest] Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-08-23 10:27 [Bug c++/102022] New: incorrect code with -O2 scu319hy at msn dot com 2021-08-23 10:30 ` [Bug c++/102022] " marxin at gcc dot gnu.org 2021-08-23 10:33 ` pinskia at gcc dot gnu.org 2021-08-23 10:36 ` pinskia at gcc dot gnu.org 2021-08-23 13:22 ` rguenth at gcc dot gnu.org 2021-08-23 13:24 ` jakub at gcc dot gnu.org
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