On Mon, Dec 19, 2016 at 8:18 PM, Timothy Arceri <
timothy.arc...@collabora.com> wrote:
> Unless an if statement contains nested returns we can simply add
> any following instructions to the branch without the return.
>
> V2: fix handling if_nested_return value when there is a sibling if/loop
> that doesn't contain a return. (Spotted by Ken)
> ---
> src/compiler/nir/nir_lower_returns.c | 37 ++++++++++++++++++++++++++++++
> ------
> 1 file changed, 31 insertions(+), 6 deletions(-)
>
> diff --git a/src/compiler/nir/nir_lower_returns.c
> b/src/compiler/nir/nir_lower_returns.c
> index cf49d5b..5eec984 100644
> --- a/src/compiler/nir/nir_lower_returns.c
> +++ b/src/compiler/nir/nir_lower_returns.c
> @@ -30,6 +30,8 @@ struct lower_returns_state {
> struct exec_list *cf_list;
> nir_loop *loop;
> nir_variable *return_flag;
> + /* Are there other return statments nested in the current if */
> + bool if_nested_return;
> };
>
> static bool lower_returns_in_cf_list(struct exec_list *cf_list,
> @@ -82,8 +84,10 @@ lower_returns_in_loop(nir_loop *loop, struct
> lower_returns_state *state)
> * flag set to true. We need to predicate everything following the
> loop
> * on the return flag.
> */
> - if (progress)
> + if (progress) {
> predicate_following(&loop->cf_node, state);
> + state->if_nested_return = true;
> + }
>
> return progress;
> }
> @@ -91,10 +95,13 @@ lower_returns_in_loop(nir_loop *loop, struct
> lower_returns_state *state)
> static bool
> lower_returns_in_if(nir_if *if_stmt, struct lower_returns_state *state)
> {
> - bool progress;
> + bool progress, then_progress;
>
> - progress = lower_returns_in_cf_list(&if_stmt->then_list, state);
> - progress = lower_returns_in_cf_list(&if_stmt->else_list, state) ||
> progress;
> + bool if_nested_return = state->if_nested_return;
> + state->if_nested_return = false;
> +
> + then_progress = lower_returns_in_cf_list(&if_stmt->then_list, state);
> + progress = lower_returns_in_cf_list(&if_stmt->else_list, state) ||
> then_progress;
>
I don't really get why we need this if_nested_return thing. Why can't we
just have two progress booleans called then_progress and else_progress and
just do
if (then_progress && else_progress) {
predicate_following
} else if (!then_progress && !else_progress) {
return false;
} else {
/* Put it in one side or the other based on progress */
}
That seems way simpler.
>
> /* If either of the recursive calls made progress, then there were
> * returns inside of the body of the if. If we're in a loop, then
> these
> @@ -106,8 +113,25 @@ lower_returns_in_if(nir_if *if_stmt, struct
> lower_returns_state *state)
> * after a return, we need to predicate everything following on the
> * return flag.
> */
> - if (progress && !state->loop)
> - predicate_following(&if_stmt->cf_node, state);
> + if (progress && !state->loop) {
> + if (state->if_nested_return) {
> + predicate_following(&if_stmt->cf_node, state);
> + } else {
> + /* If there are no nested returns we can just add the
> instructions to
> + * the end of the branch that doesn't have the return.
> + */
> + nir_cf_list list;
> + nir_cf_extract(&list, nir_after_cf_node(&if_stmt->cf_node),
> + nir_after_cf_list(state->cf_list));
> +
> + if (then_progress)
> + nir_cf_reinsert(&list, nir_after_cf_list(&if_stmt->
> else_list));
> + else
> + nir_cf_reinsert(&list, nir_after_cf_list(&if_stmt->
> then_list));
> + }
> + }
> +
> + state->if_nested_return = progress || if_nested_return;
>
> return progress;
> }
> @@ -221,6 +245,7 @@ nir_lower_returns_impl(nir_function_impl *impl)
> state.cf_list = &impl->body;
> state.loop = NULL;
> state.return_flag = NULL;
> + state.if_nested_return = false;
> nir_builder_init(&state.builder, impl);
>
> bool progress = lower_returns_in_cf_list(&impl->body, &state);
> --
> 2.9.3
>
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