[Mesa-dev] [PATCH 14/22] glsl/ast: Generate a more compact expression to disable execution of default case

[Alejandro Piñeiro]

On 21/09/17 16:34, Ian Romanick wrote:
> From: "\"Ian Romanick\"" <idr at freedesktop.org>
>
> From: Ian Romanick <ian.d.romanick at intel.com>
>
> Instead of generating a sequence like:
>
>     run_default = true;
>     if (i == 3) // some label that appears after default
>         run_default = false;
>     if (i == 4) // some label that appears after default
>         run_default = false;
>     ...
>     if (run_default) {
>         ...
>     }
>
> generate something like:
>
>     run_default = !((i == 3) || (i == 4) || ...);
>     if (run_default) {
>         ...
>     }
>
> This eliminates a use of conditional assignements, and it enables the

typo: s/assignements/assignments


> elimination of another.
>
> Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
> ---
>  src/compiler/glsl/ast_to_hir.cpp | 31 ++++++++++---------------------
>  1 file changed, 10 insertions(+), 21 deletions(-)
>
> diff --git a/src/compiler/glsl/ast_to_hir.cpp b/src/compiler/glsl/ast_to_hir.cpp
> index 1d74e24..5f751a4 100644
> --- a/src/compiler/glsl/ast_to_hir.cpp
> +++ b/src/compiler/glsl/ast_to_hir.cpp
> @@ -6589,27 +6589,11 @@ ast_case_statement_list::hir(exec_list *instructions,
>      * if default should be chosen or not.
>      */
>     if (!default_case.is_empty()) {
> -
> -      ir_rvalue *const true_val = new (state) ir_constant(true);
> -      ir_dereference_variable *deref_run_default_var =
> -         new(state) ir_dereference_variable(state->switch_state.run_default);
> -
> -      /* Choose to run default case initially, following conditional
> -       * assignments might change this.
> -       */
> -      ir_assignment *const init_var =
> -         new(state) ir_assignment(deref_run_default_var, true_val);
> -      instructions->push_tail(init_var);
> -
> -      /* Default case was the last one, no checks required. */
> -      if (after_default.is_empty()) {
> -         instructions->append_list(&default_case);
> -         return NULL;
> -      }
> -
>        struct hash_entry *entry;
>        ir_factory body(instructions, state);
>  
> +      ir_expression *cmp = NULL;
> +
>        hash_table_foreach(state->switch_state.labels_ht, entry) {
>           const struct case_label *const l = (struct case_label *) entry->data;
>  
> @@ -6623,12 +6607,17 @@ ast_case_statement_list::hir(exec_list *instructions,
>                 ? body.constant(unsigned(l->value))
>                 : body.constant(int(l->value));
>  
> -            body.emit(assign(state->switch_state.run_default,
> -                             body.constant(false),
> -                             equal(cnst, state->switch_state.test_var)));
> +            cmp = cmp == NULL
> +               ? equal(cnst, state->switch_state.test_var)
> +               : logic_or(cmp, equal(cnst, state->switch_state.test_var));
>           }
>        }
>  
> +      if (cmp != NULL)
> +         body.emit(assign(state->switch_state.run_default, logic_not(cmp)));
> +      else
> +         body.emit(assign(state->switch_state.run_default, body.constant(true)));
> +
>        /* Append default case and all cases after it. */
>        instructions->append_list(&default_case);
>        instructions->append_list(&after_default);