https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108953
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|c++ |tree-optimization
CC| |jakub at gcc dot gnu.org
--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I don't think there is anything the C++ FE should do here, user can write it
like that
by hand too:
bool check(C const& lhs, C const& rhs) {
if (lhs.a != rhs.a) return false;
if (lhs.b != rhs.b) return false;
if (lhs.c != rhs.c) return false;
if (lhs.d != rhs.d) return false;
if (lhs.e != rhs.e) return false;
if (lhs.f != rhs.f) return false;
if (lhs.g != rhs.g) return false;
return true;
}
etc., so we should pattern match this somewhere during GIMPLE opts.
The memcmp issue is a RTL issue (so I think we want actually two bugs), at
GIMPLE level it is optimized into:
_1 = __builtin_memcmp_eq (lhs_3(D), rhs_4(D), 12);
_5 = _1 == 0;
return _5;
which is I think what we want.
The reason for doing conditional branch after each comparison is
targetm.compare_by_pieces_branch_ratio (DImode) tells it not to batch more than
one.
Not really sure if we should override it to something else and on which
targets.
The reason for the weird
mov eax, 1
test eax, eax
sete al
instead of
xor eax, eax
and
xor eax, eax
test eax, eax
sete al
instead of
mov eax, 1
is that the epilogue is threaded only too late where the constant propagation
through it isn't possible.
