https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112653
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
We do use the alias oracle in folding memmove:
/* If the destination and source do not alias optimize into
memcpy as well. */
if ((is_gimple_min_invariant (dest)
|| TREE_CODE (dest) == SSA_NAME)
&& (is_gimple_min_invariant (src)
|| TREE_CODE (src) == SSA_NAME))
{
ao_ref destr, srcr;
ao_ref_init_from_ptr_and_size (&destr, dest, len);
ao_ref_init_from_ptr_and_size (&srcr, src, len);
if (!refs_may_alias_p_1 (&destr, &srcr, false))
{
tree fn;
fn = builtin_decl_implicit (BUILT_IN_MEMCPY);
if (!fn)
return false;
but the issue is that test2 escapes which makes this conflict:
# PT = null { D.2775 } (escaped, escaped heap)
# ALIGN = 8, MISALIGN = 0
# USE = nonlocal escaped
# CLB = nonlocal escaped
test2_4 = __builtin_malloc (1000);
# PT = nonlocal escaped null
test.0_1 = test;
__builtin_memmove (test2_4, test.0_1, 1000);
it works for
char *test, *test3;
void
copy_test ()
{
char *test2 = __builtin_malloc (1000);
__builtin_memmove (test2, test, 1000);
__builtin_memmove (test3, test2, 1000);
__builtin_free (test2);
}
where both memmove calls become memcpy. So this isn't asking for better
folding but for better pointer analysis I guess.
