[Mesa-dev] [PATCH 3/9] nir: Skip common instructions when comparing deref paths

[Jason Ekstrand]

Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>

On Wed, Aug 15, 2018 at 4:57 PM Caio Marcelo de Oliveira Filho <
caio.oliveira at intel.com> wrote:

> Deref paths may share the same deref instructions in their chains,
> e.g.
>
>     ssa_100 = deref_var A
>     ssa_101 = deref_struct "array_field" of ssa_100
>     ssa_102 = deref_array "[1]" of ssa_101
>     ssa_103 = deref_struct "field_a" of ssa_102
>     ssa_104 = deref_struct "field_a" of ssa_103
>
> when comparing the two last deref instructions, their paths will share
> a common sequence ssa_100, ssa_101, ssa_102.  This patch skips to next
> iteration if the deref instructions are the same.  Path[0] (the var)
> is still handled specially, so in the case above, only ssa_101 and
> ssa_102 will be skipped.
> ---
>  src/compiler/nir/nir_deref.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/src/compiler/nir/nir_deref.c b/src/compiler/nir/nir_deref.c
> index d013b423a8b..c8851688f9d 100644
> --- a/src/compiler/nir/nir_deref.c
> +++ b/src/compiler/nir/nir_deref.c
> @@ -294,6 +294,9 @@ nir_compare_deref_paths(nir_deref_path *a_path,
>        nir_deref_instr *a_tail = *(a_p++);
>        nir_deref_instr *b_tail = *(b_p++);
>
> +      if (a_tail == b_tail)
> +         continue;
> +
>        switch (a_tail->deref_type) {
>        case nir_deref_type_array:
>        case nir_deref_type_array_wildcard: {
> --
> 2.18.0
>
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