https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101105
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC|rguenther at suse dot de |rguenth at gcc dot
gnu.org,
| |rsandifo at gcc dot gnu.org
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
Last reconfirmed| |2021-06-17
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.
short a;
int b[5][4] = {2, 2};
int d;
short e(int f) { return f == 0 || a && f == 1 ? 0 : a; }
int main() {
int g, h;
g = 3;
for (; g >= 0; g--) {
h = 3;
for (; h >= 0; h--)
b[g][h] = b[0][1] && e(1);
}
d = b[0][1];
if (d != 0)
__builtin_abort ();
return 0;
}
after if-conversion we have
<bb 3> [local count: 214748368]:
# g_40 = PHI <g_11(7), 3(2)>
# ivtmp_2 = PHI <ivtmp_27(7), 4(2)>
b[g_40][2] = 0;
b[g_40][3] = 0;
b[g_40][1] = 0;
_42 = b[0][1];
b[g_40][0] = 0;
g_11 = g_40 + -1;
ivtmp_27 = ivtmp_2 - 1;
if (ivtmp_27 != 0)
goto <bb 7>; [75.00%]
else
goto <bb 4>; [25.00%]
<bb 7> [local count: 161061274]:
goto <bb 3>; [100.00%]
<bb 4> [local count: 53687093]:
# _18 = PHI <_42(3)>
d = _18;
if (_18 != 0)
and vect produces
<bb 3> [local count: 214748368]:
# g_40 = PHI <g_11(7), 3(2)>
# ivtmp_2 = PHI <ivtmp_27(7), 4(2)>
# ivtmp_48 = PHI <ivtmp_26(7), _19(2)>
# ivtmp_32 = PHI <ivtmp_12(7), 0(2)>
_42 = b[0][1];
MEM <vector(4) int> [(int *)ivtmp_48] = { 0, 0, 0, 0 };
ivtmp_31 = ivtmp_48 + 18446744073709551600(OVF);
g_11 = g_40 + -1;
ivtmp_27 = ivtmp_2 - 1;
ivtmp_26 = ivtmp_48 + 18446744073709551600(OVF);
ivtmp_12 = ivtmp_32 + 1;
if (ivtmp_12 < 4)
goto <bb 7>; [75.00%]
else
goto <bb 4>; [25.00%]
<bb 7> [local count: 161061274]:
goto <bb 3>; [100.00%]
<bb 4> [local count: 53687093]:
# _18 = PHI <_42(3)>
We have
(Data Dep:
#(Data Ref:
# bb: 3
# stmt: b[g_40][1] = 0;
# ref: b[g_40][1];
# base_object: b;
# Access function 0: 1
# Access function 1: {3, +, -1}_1
#)
#(Data Ref:
# bb: 3
# stmt: _42 = b[0][1];
# ref: b[0][1];
# base_object: b;
# Access function 0: 1
# Access function 1: 0
#)
access_fn_A: 1
access_fn_B: 1
(subscript
iterations_that_access_an_element_twice_in_A: [0]
last_conflict: scev_not_known
iterations_that_access_an_element_twice_in_B: [0]
last_conflict: scev_not_known
(Subscript distance: 0 ))
access_fn_A: {3, +, -1}_1
access_fn_B: 0
(subscript
iterations_that_access_an_element_twice_in_A: [-3]
last_conflict: 1
iterations_that_access_an_element_twice_in_B: [0]
last_conflict: 1
(Subscript distance: -3 ))
loop nest: (1 )
)
and mark the DR for a runtime alias test. But then
t3.c:8:12: note: === vect_prune_runtime_alias_test_list ===
t3.c:8:12: note: can tell at compile time that b[g_40][0] and b[0][1] do not
alias
t3.c:8:12: note: improved number of alias checks from 1 to 0
as vect_compile_time_alias gets segment_lengths of zero (huh), since
/* Step values are irrelevant for aliasing if the number of vector
iterations is equal to the number of scalar iterations (which can
happen for fully-SLP loops). */
bool ignore_step_p = known_eq (LOOP_VINFO_VECT_FACTOR (loop_vinfo), 1U);
...
if (ignore_step_p)
{
segment_length_a = size_zero_node;
segment_length_b = size_zero_node;
}
but I'm not sure if a segment length of zero will do good in any case where
the alias check is needed? Richard - that's your code, can you have a look?
