I cannot remember if I filed a bug about this or not but I noticed this while looking at some Fortran code. Here is testcase which shows the issue: void link_error(void);
int *t; int g(int *a) { t = a; *a = 2; } void f(int *a) { int b; b = 1; g(&b); b = 2; *a = 1; <--- a cannot point to b here. if (b == 2) link_error(); } int main(void) { int t; f(&t); return 0; } -- Summary: Arguments cannot alias local variables Product: gcc Version: 4.2.0 Status: UNCONFIRMED Keywords: missed-optimization, alias Severity: normal Priority: P3 Component: tree-optimization AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: pinskia at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25558