[Mesa-dev] [PATCH v4 6/7] nir: add loop unroll support for wrapper loops

[Ian Romanick]

On 08/27/2018 02:08 AM, Timothy Arceri wrote:
> This adds support for unrolling the classic
> 
>     do {
>         // ...
>     } while (false)
> 
> that is used to wrap multi-line macros. GLSL IR also wraps switch
> statements in a loop like this.

Yes!  This has been several items down on my to-do list for months.

Reviewed-by: Ian Romanick <ian.d.romanick at intel.com>
Thanked-by: Ian Romanick <ian.d.romanick at intel.com>

> 
> shader-db results IVB:
> 
> total loops in shared programs: 2515 -> 2512 (-0.12%)
> loops in affected programs: 33 -> 30 (-9.09%)
> helped: 3
> HURT: 0
> ---
>  src/compiler/nir/nir_opt_loop_unroll.c | 77 ++++++++++++++++++++++++++
>  1 file changed, 77 insertions(+)
> 
> diff --git a/src/compiler/nir/nir_opt_loop_unroll.c b/src/compiler/nir/nir_opt_loop_unroll.c
> index e0e0b754716..9c33267cb72 100644
> --- a/src/compiler/nir/nir_opt_loop_unroll.c
> +++ b/src/compiler/nir/nir_opt_loop_unroll.c
> @@ -465,6 +465,65 @@ complex_unroll(nir_loop *loop, nir_loop_terminator *unlimit_term,
>     _mesa_hash_table_destroy(remap_table, NULL);
>  }
>  
> +/* Unrolls the classic wrapper loops e.g
> + *
> + *    do {
> + *        // ...
> + *    } while (false)
> + */
> +static bool
> +wrapper_unroll(nir_loop *loop)
> +{
> +   bool progress = false;
> +
> +   nir_block *blk_after_loop =
> +      nir_cursor_current_block(nir_after_cf_node(&loop->cf_node));
> +
> +   /* There may still be some single src phis following the loop that
> +    * have not yet been cleaned up by another pass. Tidy those up before
> +    * unrolling the loop.
> +    */
> +   nir_foreach_instr_safe(instr, blk_after_loop) {
> +      if (instr->type != nir_instr_type_phi)
> +         break;
> +
> +      nir_phi_instr *phi = nir_instr_as_phi(instr);
> +      assert(exec_list_length(&phi->srcs) == 1);
> +
> +      nir_phi_src *phi_src = exec_node_data(nir_phi_src,
> +                                            exec_list_get_head(&phi->srcs),
> +                                            node);
> +
> +      nir_ssa_def_rewrite_uses(&phi->dest.ssa, phi_src->src);
> +      nir_instr_remove(instr);
> +
> +      progress = true;
> +   }
> +
> +   nir_block *last_loop_blk = nir_loop_last_block(loop);
> +   if (nir_block_ends_in_break(last_loop_blk)) {
> +
> +      /* Remove break at end of the loop */
> +      nir_instr *break_instr = nir_block_last_instr(last_loop_blk);
> +      nir_instr_remove(break_instr);
> +
> +      /* Pluck out the loop body. */
> +      nir_cf_list loop_body;
> +      nir_cf_extract(&loop_body, nir_before_block(nir_loop_first_block(loop)),
> +                     nir_after_block(nir_loop_last_block(loop)));
> +
> +      /* Reinsert loop body after the loop */
> +      nir_cf_reinsert(&loop_body, nir_after_cf_node(&loop->cf_node));
> +
> +      /* The loop has been unrolled so remove it. */
> +      nir_cf_node_remove(&loop->cf_node);
> +
> +      progress = true;
> +   }
> +
> +   return progress;
> +}
> +
>  static bool
>  is_loop_small_enough_to_unroll(nir_shader *shader, nir_loop_info *li)
>  {
> @@ -516,6 +575,24 @@ process_loops(nir_shader *sh, nir_cf_node *cf_node, bool *has_nested_loop_out)
>      */
>     if (!progress) {
>  
> +      /* Check for the classic
> +       *
> +       *    do {
> +       *        // ...
> +       *    } while (false)
> +       *
> +       * that is used to wrap multi-line macros. GLSL IR also wraps switch
> +       * statements in a loop like this.
> +       */
> +      if (loop->info->limiting_terminator == NULL &&
> +          list_empty(&loop->info->loop_terminator_list) &&
> +          !loop->info->complex_loop) {
> +
> +         progress = wrapper_unroll(loop);
> +
> +         goto exit;
> +      }
> +
>        if (has_nested_loop || loop->info->limiting_terminator == NULL)
>           goto exit;
>  
>