[Mesa-dev] [PATCH 049/133] nir: Add a function to detect if a block is immediately followed by an if

[Connor Abbott]

On Tue, Dec 16, 2014 at 1:04 AM, Jason Ekstrand <jason at jlekstrand.net> wrote:
> Since we don't actually have an "if" instruction, this is a very common
> pattern when iterating over instructions.  This adds a helper function for
> it to make things a little less painful.
> ---
>  src/glsl/nir/nir.c          | 17 +++++++++++++++++
>  src/glsl/nir/nir.h          |  5 +++++
>  src/glsl/nir/nir_from_ssa.c |  9 +++------
>  src/glsl/nir/nir_opt_dce.c  | 12 +++++-------
>  4 files changed, 30 insertions(+), 13 deletions(-)
>
> diff --git a/src/glsl/nir/nir.c b/src/glsl/nir/nir.c
> index 5dbcc77..e90eeda 100644
> --- a/src/glsl/nir/nir.c
> +++ b/src/glsl/nir/nir.c
> @@ -1686,6 +1686,23 @@ nir_foreach_block_reverse(nir_function_impl *impl, nir_foreach_block_cb cb,
>     return true;
>  }
>
> +nir_if *
> +nir_block_following_if(nir_block *block)

Could you rename this to "nir_block_get_following_if"? I read this as
"block following if" (i.e. finding the block after an if statement)
and was confused at first. Also, it's generally a good idea to name
functions with verbs.

> +{
> +   if (exec_node_is_tail_sentinel(&block->cf_node.node))
> +      return NULL;
> +
> +   if (nir_cf_node_is_last(&block->cf_node))
> +      return NULL;
> +
> +   nir_cf_node *next_node = nir_cf_node_next(&block->cf_node);
> +
> +   if (next_node->type != nir_cf_node_if)
> +      return NULL;
> +
> +   return nir_cf_node_as_if(next_node);
> +}
> +
>  static bool
>  index_block(nir_block *block, void *state)
>  {
> diff --git a/src/glsl/nir/nir.h b/src/glsl/nir/nir.h
> index 8d5f6b8..f405694 100644
> --- a/src/glsl/nir/nir.h
> +++ b/src/glsl/nir/nir.h
> @@ -1275,6 +1275,11 @@ typedef bool (*nir_foreach_block_cb)(nir_block *block, void *state);
>  bool nir_foreach_block(nir_function_impl *impl, nir_foreach_block_cb cb,
>                         void *state);
>
> +/* If the following CF node is an if, this function returns that if.
> + * Otherwise, it returns NULL.
> + */
> +nir_if *nir_block_following_if(nir_block *block);
> +
>  void nir_index_local_regs(nir_function_impl *impl);
>  void nir_index_global_regs(nir_shader *shader);
>  void nir_index_ssa_defs(nir_function_impl *impl);
> diff --git a/src/glsl/nir/nir_from_ssa.c b/src/glsl/nir/nir_from_ssa.c
> index 04c8103..a26f0c4 100644
> --- a/src/glsl/nir/nir_from_ssa.c
> +++ b/src/glsl/nir/nir_from_ssa.c
> @@ -109,12 +109,9 @@ convert_from_ssa_block(nir_block *block, void *void_state)
>        }
>     }
>
> -   if (block->cf_node.node.next != NULL && /* check that we aren't the end node */
> -       !nir_cf_node_is_last(&block->cf_node) &&
> -       nir_cf_node_next(&block->cf_node)->type == nir_cf_node_if) {
> -      nir_if *if_stmt = nir_cf_node_as_if(nir_cf_node_next(&block->cf_node));
> -      rewrite_ssa_src(&if_stmt->condition, state);
> -   }
> +   nir_if *following_if = nir_block_following_if(block);
> +   if (following_if)
> +      rewrite_ssa_src(&following_if->condition, state);
>
>     return true;
>  }
> diff --git a/src/glsl/nir/nir_opt_dce.c b/src/glsl/nir/nir_opt_dce.c
> index c18ba32..c3bbcb4 100644
> --- a/src/glsl/nir/nir_opt_dce.c
> +++ b/src/glsl/nir/nir_opt_dce.c
> @@ -123,13 +123,11 @@ init_block_cb(nir_block *block, void *_state)
>     nir_foreach_instr(block, instr)
>        init_instr(instr, worklist);
>
> -   if (block->cf_node.node.next != NULL && /* check that we aren't the end node */
> -       !nir_cf_node_is_last(&block->cf_node) &&
> -       nir_cf_node_next(&block->cf_node)->type == nir_cf_node_if) {
> -      nir_if *if_stmt = nir_cf_node_as_if(nir_cf_node_next(&block->cf_node));
> -      if (if_stmt->condition.is_ssa &&
> -          !if_stmt->condition.ssa->parent_instr->live)
> -         worklist_push(worklist, if_stmt->condition.ssa->parent_instr);
> +   nir_if *following_if = nir_block_following_if(block);
> +   if (following_if) {
> +      if (following_if->condition.is_ssa &&
> +          !following_if->condition.ssa->parent_instr->live)
> +         worklist_push(worklist, following_if->condition.ssa->parent_instr);
>     }
>
>     return true;
> --
> 2.2.0
>
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