https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127130
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot
gnu.org
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
So the issue lies with SCEV. We get
(get_scalar_evolution
(scalar = _4)
(scalar_evolution = {-66, +, -97}<nw>_1))
for
<bb 3> [local count: 955630224]:
# n.0_44 = PHI <_24(5), 20158(2)>
# _45 = PHI <_3(5), -66(2)>
# ivtmp_67 = PHI <ivtmp_66(5), 2(2)
..
_4 = (int) _45;
..
n.22_22 = (unsigned short) n.0_44;
_23 = n.22_22 + 6303;
_24 = (short int) _23;
..
_3 = (signed char) _23;
..
ivtmp_66 = ivtmp_67 - 1;
if (ivtmp_66 == 0)
goto <bb 4>; [11.00%]
else
goto <bb 5>; [89.00%]
<bb 5> [local count: 850510900]:
goto <bb 3>; [100.00%]
with the cycles analyzed to
(set_scalar_evolution
instantiated_below = 2
(scalar = n.0_44)
(scalar_evolution = {20158, +, 6303}_1))
(instantiate_scev
(instantiate_below = 2 -> 3)
(evolution_loop = 1)
(chrec = {93, +, -97}_1)
(res = {93, +, -97}_1))
Simplify PEELED_CHREC into POLYNOMIAL_CHREC.
(evolution_function = {-66, +, -97}_1))
(set_scalar_evolution
instantiated_below = 2
(scalar = _45)
(scalar_evolution = {-66, +, -97}_1))
)
simplify_peeled_chrec turns {93, +, -97}_1 into {-66, +, -97}_1 with
left = CHREC_LEFT (ev);
right = CHREC_RIGHT (ev);
type = TREE_TYPE (left);
step_val = chrec_fold_plus (type, init_cond, right);
/* Transform (init, {left, right}_LOOP)_LOOP to {init, right}_LOOP
if "left" equals to "init + right". */
if (operand_equal_p (left, step_val, 0))
{
if (dump_file && (dump_flags & TDF_SCEV))
fprintf (dump_file, "Simplify PEELED_CHREC into POLYNOMIAL_CHREC.\n");
return build_polynomial_chrec (loop->num, init_cond, right);
}
but here init_cond + right overflows (-66 + -97), we get 93(OVF). The
following "try harder" code does not seem to care about overflow either.
