On Sep 20, 2017, at 2:14 PM, Bill Schmidt <[email protected]> wrote:
>
> On Sep 20, 2017, at 3:49 AM, Richard Sandiford <[email protected]>
> wrote:
>>
>> But I think this shows up another problem. In the vectorised loop,
>> we have 1 copy of the load and 4 copies of the ABS (after unpacking).
>> But vect_analyze_slp_cost_1 is being called with ncopies_for_cost == 4
>> even for the loads. So I think it's a double whammy: we've quadrupling
>> the real cost via the excessive ncopies_for_cost, and we're using the
>> wrong access type too.
>>
>> The patch below should fix the second problem but isn't much use without
>> the first. I think we need to adjust ncopies_for_cost in the recursive
>> calls as well.
>
> Unfortunately we have to deal with the fact that ncopies_for_cost is set
> once for the whole SLP instance, which is not ideal since we know the
> number of loads and stores doesn't follow the same rules.
>
> What about the following? I *think* that group_size / nunits is sufficient
> for
> VMAT_STRIDED_SLP and VMAT_CONTIGUOUS for which permuted loads are
> not possible (already handled differently), but I could well be missing
> something.
Uh, I need to do the obvious rounding of (group_size + nunits - 1) / nunits...
Bill
>
> Index: gcc/tree-vect-slp.c
> ===================================================================
> --- gcc/tree-vect-slp.c (revision 252760)
> +++ gcc/tree-vect-slp.c (working copy)
> @@ -1662,12 +1662,14 @@ vect_analyze_slp_cost_1 (slp_instance instance, sl
> stmt_info = vinfo_for_stmt (stmt);
> if (STMT_VINFO_GROUPED_ACCESS (stmt_info))
> {
> + int group_size = GROUP_SIZE (stmt_info);
> + int nunits = TYPE_VECTOR_SUBPARTS (STMT_VINFO_VECTYPE (stmt_info));
> vect_memory_access_type memory_access_type
> - = (STMT_VINFO_STRIDED_P (stmt_info)
> + = (STMT_VINFO_STRIDED_P (stmt_info) && group_size > nunits
> ? VMAT_STRIDED_SLP
> : VMAT_CONTIGUOUS);
> if (DR_IS_WRITE (STMT_VINFO_DATA_REF (stmt_info)))
> - vect_model_store_cost (stmt_info, ncopies_for_cost,
> + vect_model_store_cost (stmt_info, group_size / nunits,
> memory_access_type, vect_uninitialized_def,
> node, prologue_cost_vec, body_cost_vec);
> else
> @@ -1714,6 +1716,8 @@ vect_analyze_slp_cost_1 (slp_instance instance, sl
> + nunits - 1) / nunits);
> ncopies_for_cost *= SLP_INSTANCE_UNROLLING_FACTOR (instance);
> }
> + else
> + ncopies_for_cost = group_size / nunits;
> /* Record the cost for the vector loads. */
> vect_model_load_cost (stmt_info, ncopies_for_cost,
> memory_access_type, node, prologue_cost_vec,
>
> Bill
>
