https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101178
Bug ID: 101178
Summary: SLP permute propagation doesn't handle VEC_PERM
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: rguenth at gcc dot gnu.org
Target Milestone: ---
The current permute propagation code simply treats VEC_PERM nodes as
materialization points (they can consume incoming permutes) but it does
neither handle them as sources for permutes nor does it consider propagating
a common source permute through itself. The latter can be seen for
double x[2], y[2], z[2], w[2];
void foo ()
{
double tem0 = x[1] + y[1];
double tem1 = x[0] - y[0];
double tem2 = z[1] * tem0;
double tem3 = z[0] * tem1;
z[0] = tem2 - w[0];
z[1] = tem3 + w[1];
}
where we do not end up materializing the x[], y[] and w[] permute at
the last +- node but instead materialize at the first +- node and thus
end up with incoming permute differences at the second +- one:
<bb 2> [local count: 1073741824]:
_21 = &x[1] + 18446744073709551608;
vect__3.9_22 = MEM <vector(2) double> [(double *)_21];
_1 = x[1];
_23 = &y[1] + 18446744073709551608;
vect__4.12_24 = MEM <vector(2) double> [(double *)_23];
vect_tem1_13.14_26 = vect__3.9_22 - vect__4.12_24;
vect_tem0_12.13_25 = vect__3.9_22 + vect__4.12_24;
_27 = VEC_PERM_EXPR <vect_tem0_12.13_25, vect_tem1_13.14_26, { 1, 2 }>;
_2 = y[1];
tem0_12 = _1 + _2;
_3 = x[0];
_4 = y[0];
tem1_13 = _3 - _4;
_18 = &z[1] + 18446744073709551608;
vect__5.5_19 = MEM <vector(2) double> [(double *)_18];
vect__6.6_20 = VEC_PERM_EXPR <vect__5.5_19, vect__5.5_19, { 1, 0 }>;
vect_tem2_14.15_28 = vect__6.6_20 * _27;
_5 = z[1];
tem2_14 = _5 * tem0_12;
_6 = z[0];
tem3_15 = _6 * tem1_13;
vect__7.18_29 = MEM <vector(2) double> [(double *)&w];
vect__10.20_31 = vect_tem2_14.15_28 + vect__7.18_29;
vect__8.19_30 = vect_tem2_14.15_28 - vect__7.18_29;
_32 = VEC_PERM_EXPR <vect__8.19_30, vect__10.20_31, { 0, 3 }>;
_7 = w[0];
_8 = tem2_14 - _7;
_9 = w[1];
_10 = _9 + tem3_15;
MEM <vector(2) double> [(double *)&z] = _32;
The permute vect__6.6_20 = VEC_PERM_EXPR <vect__5.5_19, vect__5.5_19, { 1, 0 }>
could have been elided.
