https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91294
Bug ID: 91294
Summary: [10 Regression] wrong strlen result of a conditional
with an offset
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
r273783 committed last week to resolve pr91183 introduced a couple of bugs into
the strlen pass: when copying the result of a conditional expression involving
source strings of different lengths into a destination containing a string, the
length of the result isn't computed correctly. Instead of using the length of
the shorter of the two source strings (adjusted for any offset into the
destination) as the lower bound of the result the optimization use the length
of the shorter source (again adjusted for any offset into the destination) as
the exact length of the result. The program below includes two test cases, one
for each instance of this bug (it's in two places).
$ cat z.c && gcc -O2 -Wall z.c && ./a.out
const char s[] = "76543210\0\0";
const char t[] = "01234567\0\0";
char a[16], b[16];
int i = 0;
int f (void)
{
__builtin_memcpy (a, i ? s + 2 : t + 1, 8);
return __builtin_strlen (a);
}
int g (void)
{
__builtin_strcpy (b, "12345678");
__builtin_strcat (b, "9a");
__builtin_memcpy (b + 6, i ? "78\0" : "789\0", 4);
return __builtin_strlen (b);
}
int main (void)
{
__builtin_printf ("strlen (\"%s\") = %i\n", a, f ());
__builtin_printf ("strlen (\"%s\") = %i\n", b, g ());
}
strlen ("1234567") = 6
strlen ("123456789") = 8
