https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107160
--- Comment #9 from Kewen Lin <linkw at gcc dot gnu.org> ---
>
> The above doesn't look wrong (but may miss the rest of the IL). On
> x86_64 this looks like
>
> <bb 4> [local count: 105119324]:
> # sum0_41 = PHI <sum0_28(3)>
> # sum1_39 = PHI <sum1_29(3)>
> # sum2_37 = PHI <sum2_30(3)>
> # sum3_35 = PHI <sum3_31(3)>
> # vect_sum3_31.11_59 = PHI <vect_sum3_31.11_60(3)>
> _58 = BIT_FIELD_REF <vect_sum3_31.11_59, 32, 0>;
> _57 = BIT_FIELD_REF <vect_sum3_31.11_59, 32, 32>;
> _56 = BIT_FIELD_REF <vect_sum3_31.11_59, 32, 64>;
> _55 = BIT_FIELD_REF <vect_sum3_31.11_59, 32, 96>;
> _74 = _58 + _57;
> _76 = _56 + _74;
> _78 = _55 + _76;
>
> <bb 5> [local count: 118111600]:
> # prephitmp_79 = PHI <_78(4), 0.0(2)>
> return prephitmp_79;
>
Yeah, it looks expected without unrolling.
> when unrolling is applied, thus with a larger VF, you should ideally
> see the vectors accumulated.
>
> Btw, I've fixed a SLP reduction issue two days ago in
> r13-3226-gee467644c53ee2
> though that looks unrelated?
Thanks for the information, I'll double check it.
>
> When I force a larger VF on x86 by adding a int store in the loop I see
>
> <bb 11> [local count: 94607391]:
> # sum0_48 = PHI <sum0_29(3)>
> # sum1_36 = PHI <sum1_30(3)>
> # sum2_35 = PHI <sum2_31(3)>
> # sum3_24 = PHI <sum3_32(3)>
> # vect_sum3_32.16_110 = PHI <vect_sum3_32.16_106(3)>
> # vect_sum3_32.16_111 = PHI <vect_sum3_32.16_107(3)>
> # vect_sum3_32.16_112 = PHI <vect_sum3_32.16_108(3)>
> # vect_sum3_32.16_113 = PHI <vect_sum3_32.16_109(3)>
> _114 = BIT_FIELD_REF <vect_sum3_32.16_110, 32, 0>;
> _115 = BIT_FIELD_REF <vect_sum3_32.16_110, 32, 32>;
> _116 = BIT_FIELD_REF <vect_sum3_32.16_110, 32, 64>;
> _117 = BIT_FIELD_REF <vect_sum3_32.16_110, 32, 96>;
> _118 = BIT_FIELD_REF <vect_sum3_32.16_111, 32, 0>;
> _119 = BIT_FIELD_REF <vect_sum3_32.16_111, 32, 32>;
> _120 = BIT_FIELD_REF <vect_sum3_32.16_111, 32, 64>;
> _121 = BIT_FIELD_REF <vect_sum3_32.16_111, 32, 96>;
> _122 = BIT_FIELD_REF <vect_sum3_32.16_112, 32, 0>;
> _123 = BIT_FIELD_REF <vect_sum3_32.16_112, 32, 32>;
> _124 = BIT_FIELD_REF <vect_sum3_32.16_112, 32, 64>;
> _125 = BIT_FIELD_REF <vect_sum3_32.16_112, 32, 96>;
> _126 = BIT_FIELD_REF <vect_sum3_32.16_113, 32, 0>;
> _127 = BIT_FIELD_REF <vect_sum3_32.16_113, 32, 32>;
> _128 = BIT_FIELD_REF <vect_sum3_32.16_113, 32, 64>;
> _129 = BIT_FIELD_REF <vect_sum3_32.16_113, 32, 96>;
> _130 = _114 + _118;
> _131 = _115 + _119;
> _132 = _116 + _120;
> _133 = _117 + _121;
> _134 = _130 + _122;
> _135 = _131 + _123;
> _136 = _132 + _124;
> _137 = _133 + _125;
> _138 = _134 + _126;
>
> see how the lanes from the different vectors are accumulated? (yeah,
> we should simply add the vectors!)
Yes, it's the same as what I saw on ppc64le, but the closely following dce6
removes the three vect_sum3_32 (in your dump, they are
vect_sum3_32.16_10{7,8,9}) as the subsequent joints don't actually use the
separated accumulated lane values (_138 -> sum0 ...) but only use
vect_sum3_32.16_110.
