https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128163
Bug ID: 128163
Summary: wrong code at -O1: store through the pointer argument
of an [[unsequenced]] function declared without a
prototype is ignored
Product: gcc
Version: 17.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: yuki.tanaka at defaultcase dot de
Target Milestone: ---
int a() [[unsequenced]];
__attribute__((noipa)) int a(int *x)
{
*x = 5;
return 1;
}
int main(void)
{
int v = 0;
a(&v);
if (v != 5)
__builtin_abort();
return 0;
}
Compiler Explorer:
ASM generation compiler returned: 0
Execution build compiler returned: 0
Program returned: 134
Program terminated with signal SIGABRT (6)
The definition of a has the pointer parameter x, and an unsequenced function
may modify an object through a pointer parameter. a(&v) stores 5 to v, so v
must be 5 after the call and the program must exit with 0, as it does at -O0.
Instead GCC assumes that v is still 0 after the call and main aborts.
https://godbolt.org/z/WYfK78jPr
Also fails at -O1, with [[reproducible]] and with __attribute__((unsequenced)).
With the prototype int a(int *) [[unsequenced]]; the program exits with 0.
