On Tue, Jan 12, 2016 at 3:51 PM, Kumar, Venkataramanan
<venkataramanan.ku...@amd.com> wrote:
> Hi
>
> The code below it looks like we always call “vect_permute_load_chain” to
> load non-unit strides of size powers of 2.
>
> (---snip---)
> /* If reassociation width for vector type is 2 or greater target machine can
> execute 2 or more vector instructions in parallel. Otherwise try to
> get chain for loads group using vect_shift_permute_load_chain. */
> mode = TYPE_MODE (STMT_VINFO_VECTYPE (vinfo_for_stmt (stmt)));
>
> if (targetm.sched.reassociation_width (VEC_PERM_EXPR, mode) > 1
> || exact_log2 (size) != -1
> || !vect_shift_permute_load_chain (dr_chain, size, stmt,
> gsi, &result_chain))
> vect_permute_load_chain (dr_chain, size, stmt, gsi, &result_chain);
>
> static bool
> vect_shift_permute_load_chain (vec<tree> dr_chain,
> unsigned int length,
> gimple *stmt,
> gimple_stmt_iterator *gsi,
> vec<tree> *result_chain)
> {
> …...
> …...
> if (exact_log2 (length) != -1 && LOOP_VINFO_VECT_FACTOR (loop_vinfo) > 4) ⇐
> This is not used.
> {
> unsigned int j, log_length = exact_log2 (length);
> for (i = 0; i < nelt / 2; ++i)
> sel[i] = i * 2;
> for (i = 0; i < nelt / 2; ++i)
> sel[nelt / 2 + i] = i * 2 + 1;
> (---snip------)
>
>
> Is there any reason to do so?
No idea, benchmarking or history probably
(vect_shift_permute_load_chain not handlinging size != 3).
> I have not done any benchmarking, but tried simple test cases for -mavx
> targets with sizes 2, 4 and VF > 4 (short/char types).
> Looks like using vect_shift_permute_load_chain seems better.
>
> Should we change it to something like this ?
>
> diff --git a/gcc/tree-vect-data-refs.c b/gcc/tree-vect-data-refs.c
> index d0e20da..b0f0a02 100644
> --- a/gcc/tree-vect-data-refs.c
> +++ b/gcc/tree-vect-data-refs.c
> @@ -5733,9 +5733,9 @@ vect_transform_grouped_load (gimple *stmt, vec<tree>
> dr_chain, int size,
> get chain for loads group using vect_shift_permute_load_chain. */
> mode = TYPE_MODE (STMT_VINFO_VECTYPE (vinfo_for_stmt (stmt)));
> if (targetm.sched.reassociation_width (VEC_PERM_EXPR, mode) > 1
> - || exact_log2 (size) != -1
> - || !vect_shift_permute_load_chain (dr_chain, size, stmt,
> - gsi, &result_chain))
> + || (!vect_shift_permute_load_chain (dr_chain, size, stmt,
> + gsi, &result_chain)
> + && exact_log2 (size) != -1))
Iff then the exact_log2 check should be simply dropped. It doesn't
make much sense with shift_permute_laod_chain
supporting power-of-two size.
Of course only benchmarking will tell ;)
Richard.
> vect_permute_load_chain (dr_chain, size, stmt, gsi, &result_chain);
> vect_record_grouped_load_vectors (stmt, result_chain);
> result_chain.release ();
>
> regards,
> Venkat.
