https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101944
Bug ID: 101944
Summary: suboptimal SLP for reduced case from namd_r
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: linkw at gcc dot gnu.org
Target Milestone: ---
For SPEC2017 bmk 508.namd_r, it's observed that it degraded by -3.73%
at -O2 -ftree-slp-vectorize vs baseline -O2 on Power9 with either default cost
model or very cheap cost model. By isolating functions, several functions are
responsible for it. One typical case is the below reduced one:
------------- TEST CASE
typedef double BigReal;
extern BigReal table_four_i[8];
extern void func1(BigReal *);
extern void func2(BigReal *);
extern void func3(BigReal, BigReal, BigReal, BigReal);
void foo(BigReal scaling, BigReal *A1, BigReal *B1, BigReal diffa) {
BigReal vdwEnergy = 0;
func1(&vdwEnergy);
const BigReal A = scaling * *A1;
const BigReal B = scaling * *B1;
BigReal vdw_d = A * table_four_i[0] - B * table_four_i[2];
BigReal vdw_c = A * table_four_i[1] - B * table_four_i[3];
BigReal vdw_b = A * table_four_i[4] - B * table_four_i[6];
BigReal vdw_a = A * table_four_i[5] - B * table_four_i[7];
register BigReal vdw_val =
((diffa * vdw_d * (1 / 6.) + vdw_c * (1 / 4.)) * diffa +
vdw_b * (1 / 2.)) * diffa + vdw_a;
vdwEnergy -= vdw_val;
func2 (&vdwEnergy);
func3 (vdw_a, vdw_b, vdw_c, vdw_d);
}
-------------
Options: -O2 -ffast-math -ftree-slp-vectorize -mcpu=power9
Scalar version at optimized dumping:
func1 (&vdwEnergy);
_1 = *A1_32(D);
A_34 = _1 * scaling_33(D);
_2 = *B1_35(D);
B_36 = _2 * scaling_33(D);
_3 = table_four_i[0];
_5 = table_four_i[2];
_6 = _5 * B_36;
vdw_d_37 = .FMS (_3, A_34, _6);
_7 = table_four_i[1];
_9 = table_four_i[3];
_10 = _9 * B_36;
vdw_c_38 = .FMS (_7, A_34, _10);
_11 = table_four_i[4];
_13 = table_four_i[6];
_14 = _13 * B_36;
vdw_b_39 = .FMS (_11, A_34, _14);
_15 = table_four_i[5];
_17 = table_four_i[7];
_18 = _17 * B_36;
vdw_a_40 = .FMS (_15, A_34, _18);
_51 = diffa_41(D) *
1.666666666666666574148081281236954964697360992431640625e-1;
_21 = vdw_c_38 * 2.5e-1;
_22 = .FMA (vdw_d_37, _51, _21);
_24 = vdw_b_39 * 5.0e-1;
_25 = .FMA (_22, diffa_41(D), _24);
_26 = _25 * diffa_41(D);
vdwEnergy.0_27 = vdwEnergy;
_49 = _18 + vdwEnergy.0_27;
_52 = .FMA (_15, A_34, _26);
_28 = _49 - _52;
vdwEnergy = _28;
func2 (&vdwEnergy);
Vector version at optimized dumping:
func1 (&vdwEnergy);
_1 = *A1_32(D);
A_34 = _1 * scaling_33(D);
_49 = {A_34, A_34};
_2 = *B1_35(D);
B_36 = _2 * scaling_33(D);
_54 = {B_36, B_36};
vect__3.6_48 = MEM <vector(2) double> [(double *)&table_four_i];
vect__5.10_52 = MEM <vector(2) double> [(double *)&table_four_i + 16B];
vect__6.11_55 = vect__5.10_52 * _54;
vect_vdw_d_37.12_56 = .FMS (vect__3.6_48, _49, vect__6.11_55);
_58 = BIT_FIELD_REF <vect_vdw_d_37.12_56, 64, 64>;
_57 = BIT_FIELD_REF <vect_vdw_d_37.12_56, 64, 0>;
_11 = table_four_i[4];
_13 = table_four_i[6];
_14 = _13 * B_36;
vdw_b_39 = .FMS (_11, A_34, _14);
_15 = table_four_i[5];
_17 = table_four_i[7];
_18 = _17 * B_36;
vdw_a_40 = .FMS (_15, A_34, _18);
_51 = diffa_41(D) *
1.666666666666666574148081281236954964697360992431640625e-1;
_59 = {_51, 2.5e-1};
vect__20.13_60 = vect_vdw_d_37.12_56 * _59;
_61 = .REDUC_PLUS (vect__20.13_60);
_24 = vdw_b_39 * 5.0e-1;
_25 = .FMA (diffa_41(D), _61, _24);
_26 = _25 * diffa_41(D);
vdwEnergy.0_27 = vdwEnergy;
_66 = _18 + vdwEnergy.0_27;
_68 = .FMA (_15, A_34, _26);
_28 = _66 - _68;
vdwEnergy = _28;
func2 (&vdwEnergy);
reduc.c:24:34: note: Cost model analysis for part in loop 0:
Vector cost: 16
Scalar cost: 17
