[Mesa-dev] [PATCH 08/13] nir: add control flow helpers for loop unrolling

[Connor Abbott]

I already noted in patch 12/13 that you can get rid of your use of
stitch_blocks(). I also don't get why you need a special
nir_cf_loop_list_extract() here... why

On Mon, Aug 29, 2016 at 12:59 AM, Timothy Arceri
<timothy.arceri at collabora.com> wrote:
> This makes stitch_blocks() available for use else where, and adds
> a new helper that extracts a cf list without worrying about
> validation.

I already noted in patch 12/13 that you can get rid of your use of
stitch_blocks(). I also don't get why you need a special
nir_cf_loop_list_extract() here... why can't you use nir_cf_extract()?
The only difference between the two is that nir_cf_extract()
re-stitches the nodes together, and it also makes sure that you don't
handle phi nodes incorrectly, but AFAICT those differences don't
matter for the way you intend to use it.

> ---
>  src/compiler/nir/nir_control_flow.c | 34 ++++++++++++++++++++++++++++++++--
>  src/compiler/nir/nir_control_flow.h |  5 +++++
>  2 files changed, 37 insertions(+), 2 deletions(-)
>
> diff --git a/src/compiler/nir/nir_control_flow.c b/src/compiler/nir/nir_control_flow.c
> index a485e71..ed8cd24 100644
> --- a/src/compiler/nir/nir_control_flow.c
> +++ b/src/compiler/nir/nir_control_flow.c
> @@ -628,8 +628,7 @@ update_if_uses(nir_cf_node *node)
>   * Stitch two basic blocks together into one. The aggregate must have the same
>   * predecessors as the first and the same successors as the second.
>   */
> -
> -static void
> +void
>  stitch_blocks(nir_block *before, nir_block *after)
>  {
>     /*
> @@ -791,6 +790,37 @@ nir_cf_extract(nir_cf_list *extracted, nir_cursor begin, nir_cursor end)
>     stitch_blocks(block_before, block_after);
>  }
>
> +/**
> + * Its not really possible to extract control flow from a loop while keeping
> + * the cf valid so this function just rips out what we ask for and any
> + * validation and fix ups are left to the caller.
> + */
> +void
> +nir_cf_loop_list_extract(nir_cf_list *extracted, nir_cf_node *begin,
> +                         nir_cf_node *end)
> +{
> +   extracted->impl = nir_cf_node_get_function(begin);
> +   exec_list_make_empty(&extracted->list);
> +
> +   /* Dominance and other block-related information is toast. */
> +   nir_metadata_preserve(extracted->impl, nir_metadata_none);
> +
> +   nir_cf_node *cf_node = begin;
> +   nir_cf_node *cf_node_end = end;
> +   while (true) {
> +      nir_cf_node *next = nir_cf_node_next(cf_node);
> +
> +      exec_node_remove(&cf_node->node);
> +      cf_node->parent = NULL;
> +      exec_list_push_tail(&extracted->list, &cf_node->node);
> +
> +      if (cf_node == cf_node_end)
> +         break;
> +
> +      cf_node = next;
> +   }
> +}
> +
>  void
>  nir_cf_reinsert(nir_cf_list *cf_list, nir_cursor cursor)
>  {
> diff --git a/src/compiler/nir/nir_control_flow.h b/src/compiler/nir/nir_control_flow.h
> index b71382f..0d97486 100644
> --- a/src/compiler/nir/nir_control_flow.h
> +++ b/src/compiler/nir/nir_control_flow.h
> @@ -78,6 +78,9 @@ nir_cf_node_insert_end(struct exec_list *list, nir_cf_node *node)
>     nir_cf_node_insert(nir_after_cf_list(list), node);
>  }
>
> +void
> +stitch_blocks(nir_block *before, nir_block *after);
> +
>
>  /** Control flow motion.
>   *
> @@ -148,6 +151,8 @@ nir_cf_list_extract(nir_cf_list *extracted, struct exec_list *cf_list)
>                    nir_after_cf_list(cf_list));
>  }
>
> +void nir_cf_loop_list_extract(nir_cf_list *extracted, nir_cf_node *begin, nir_cf_node *end);
> +
>  /** removes a control flow node, doing any cleanup necessary */
>  static inline void
>  nir_cf_node_remove(nir_cf_node *node)
> --
> 2.7.4
>
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