https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80130
Bug ID: 80130
Summary: Wrong diagnostic: dereferencing type-punned pointer
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: ahmad at a3f dot at
Target Milestone: ---
/* gcc -c -Wstrict-aliasing -fstrict-aliasing snippet.c */
union punu {
char _Alignas(_Alignof(int)) buf[sizeof(int)];
int i;
};
extern char _Alignas(_Alignof(int)) buf[sizeof(int)];
int main(void) {
int i;
/* (1) Warning: dereferencing type-punned pointer will break
strict-aliasing rules */
i = *(int*)buf;
/* (2) No warning */
union punu* u = (union punu*)buf;
i = *(int*)u;
/* (3) Warning: dereferencing type-punned pointer will break
strict-aliasing rules */
i = *(int*)(union punu*)buf;
return i;
}
On Compiler Explorer: https://godbolt.org/g/n13LRq
Is (2) a permissible way to tell GCC that buf and i may share the same memory?
In any case, (2) and (3) should exhibit the same behavior.
