[Mesa-dev] [PATCH] nir: Do not use progress for unreachable code in return lowering.

[Timothy Arceri]

On 23/04/18 03:26, Bas Nieuwenhuizen wrote:
> We seems to use progress for two cases:

seems -> seem

> 1) When we lowered some returns.
> 2) When we remove unreachable code.
> 
> If just case 2 happens we assert as state->return_flag has not
> been allocated yet, but we are still trying to do insert all
> predicates based on it.
> 
> This splits the concerns. We only use progress internally for case 1
> and then keep track of 2 in a separate variable to indicate progress
> in the return value of the pass.
> 
> This is slightly better than transforming the assert into
> if (!state->return_flag) return, as it avoids inserting predicates

"as it avoids" -> "as that would avoid" ?

> even if some other part of the code might need them.
> 
> Fixes: 6e22ad6edc "nir: return early when lowering a return at the end of a function"
> CC: 18.1 <mesa-stable at lists.freedesktop.org>

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106174

Reviewed-by: Timothy Arceri <tarceri at itsqueeze.com>

Thanks for fixing!

> ---
>   src/compiler/nir/nir_lower_returns.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/src/compiler/nir/nir_lower_returns.c b/src/compiler/nir/nir_lower_returns.c
> index 3ea69e2520..9c4881112e 100644
> --- a/src/compiler/nir/nir_lower_returns.c
> +++ b/src/compiler/nir/nir_lower_returns.c
> @@ -37,6 +37,8 @@ struct lower_returns_state {
>       * needs to be predicated on the return flag variable.
>       */
>      bool has_predicated_return;
> +
> +   bool removed_unreachable_code;
>   };
>   
>   static bool lower_returns_in_cf_list(struct exec_list *cf_list,
> @@ -162,8 +164,9 @@ lower_returns_in_block(nir_block *block, struct lower_returns_state *state)
>             */
>            return false;
>         } else {
> +         state->removed_unreachable_code = true;
>            nir_cf_delete(&list);
> -         return true;
> +         return false;
>         }
>      }
>   
> @@ -262,9 +265,11 @@ nir_lower_returns_impl(nir_function_impl *impl)
>      state.loop = NULL;
>      state.return_flag = NULL;
>      state.has_predicated_return = false;
> +   state.removed_unreachable_code = false;
>      nir_builder_init(&state.builder, impl);
>   
>      bool progress = lower_returns_in_cf_list(&impl->body, &state);
> +   progress = progress || state.removed_unreachable_code;
>   
>      if (progress) {
>         nir_metadata_preserve(impl, nir_metadata_none);
>