http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58981
--- Comment #6 from H.J. Lu <hjl.tools at gmail dot com> --- A testcase for memcpy: [hjl@gnu-32 gcc]$ cat /tmp/memcpy-2.c /* { dg-do run } */ /* { dg-options "-O2 -minline-all-stringops" } */ extern void abort (void); extern void exit (int); #define MAX_OFFSET (sizeof (long long)) #define MAX_COPY (8 * sizeof (long long)) #define MAX_EXTRA (sizeof (long long)) #define MAX_LENGTH (MAX_OFFSET + MAX_COPY + MAX_EXTRA) static union { char buf[MAX_LENGTH]; long long align_int; long double align_fp; } u; char A[MAX_LENGTH]; main () { int off, len, i; char *p, *q; for (i = 0; i < MAX_LENGTH; i++) A[i] = 'A'; for (off = 0; off < MAX_OFFSET; off++) for (len = 1; len < MAX_COPY; len++) { for (i = 0; i < MAX_LENGTH; i++) u.buf[i] = 'a'; p = __builtin_memcpy (u.buf + off, A, len); if (p != u.buf + off) abort (); q = u.buf; for (i = 0; i < off; i++, q++) if (*q != 'a') abort (); for (i = 0; i < len; i++, q++) if (*q != 'A') abort (); for (i = 0; i < MAX_EXTRA; i++, q++) if (*q != 'a') abort (); } exit(0); } [hjl@gnu-32 gcc]$ ./xgcc -B./ -O2 -mx32 /tmp/memcpy-2.c -minline-all-stringops [hjl@gnu-32 gcc]$ ./a.out Segmentation fault [hjl@gnu-32 gcc]$