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nir/opt_if: merge two break statements from both branch legs

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This optimization turns

     loop {
        ...
        if (cond) {
           do_work_1();
           break;
        } else {
           do_work_2();
           break;
        }
     }

 into:

     loop {
        ...
        if (cond) {
           do_work_1();
        } else {
           do_work_2();
        }
        break;
     }

Reviewed-by: Emma Anholt <emma@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7587>
This commit is contained in:
Daniel Schürmann
2020-11-09 21:28:08 +01:00
committed by Marge Bot
parent 64a51293c8
commit dad609d152
1 changed files with 68 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

73
src/compiler/nir/nir_opt_if.c
View File

@@ -930,6 +930,64 @@ opt_if_simplification(nir_builder *b, nir_if *nif)
return true;
}
/**
* This optimization tries to merge two break statements into a single break.
* For this purpose, it checks if both branch legs end in a break.
*
* This optimization turns
*
* loop {
* ...
* if (cond) {
* do_work_1();
* break;
* } else {
* do_work_2();
* break;
* }
* }
*
* into:
*
* loop {
* ...
* if (cond) {
* do_work_1();
* } else {
* do_work_2();
* }
* break;
* }
*
*/
static bool
opt_merge_breaks(nir_if *nif)
{
nir_block *last_then = nir_if_last_then_block(nif);
nir_block *last_else = nir_if_last_else_block(nif);
bool then_break = nir_block_ends_in_break(last_then);
bool else_break = nir_block_ends_in_break(last_else);
/* If both branch legs end in a break, merge the break after the branch */
if (then_break && else_break) {
nir_block *after_if = nir_cf_node_cf_tree_next(&nif->cf_node);
/* Make sure that the successor is empty.
* If not we let nir_opt_dead_cf() clean it up first.
*/
if (!is_block_empty(after_if))
return false;
nir_lower_phis_to_regs_block(last_then->successors[0]);
nir_instr_remove_v(nir_block_last_instr(last_then));
nir_instr *jump = nir_block_last_instr(last_else);
nir_instr_remove_v(jump);
nir_instr_insert(nir_after_block(after_if), jump);
return true;
}
return false;
}
/**
* This optimization simplifies potential loop terminators which then allows
* other passes such as opt_if_simplification() and loop unrolling to progress
@@ -1443,8 +1501,12 @@ opt_if_cf_list(nir_builder *b, struct exec_list *cf_list,
return progress;
}
/**
* Optimizations which can create registers are done after other optimizations
* which require SSA.
*/
static bool
opt_peel_loop_initial_if_cf_list(struct exec_list *cf_list)
opt_if_regs_cf_list(struct exec_list *cf_list)
{
bool progress = false;
foreach_list_typed(nir_cf_node, cf_node, node, cf_list) {
@@ -1454,14 +1516,15 @@ opt_peel_loop_initial_if_cf_list(struct exec_list *cf_list)
case nir_cf_node_if: {
nir_if *nif = nir_cf_node_as_if(cf_node);
progress |= opt_peel_loop_initial_if_cf_list(&nif->then_list);
progress |= opt_peel_loop_initial_if_cf_list(&nif->else_list);
progress |= opt_if_regs_cf_list(&nif->then_list);
progress |= opt_if_regs_cf_list(&nif->else_list);
progress |= opt_merge_breaks(nif);
break;
}
case nir_cf_node_loop: {
nir_loop *loop = nir_cf_node_as_loop(cf_node);
progress |= opt_peel_loop_initial_if_cf_list(&loop->body);
progress |= opt_if_regs_cf_list(&loop->body);
progress |= opt_peel_loop_initial_if(loop);
break;
}
@@ -1537,7 +1600,7 @@ nir_opt_if(nir_shader *shader, bool aggressive_last_continue)
progress = true;
}
if (opt_peel_loop_initial_if_cf_list(&function->impl->body)) {
if (opt_if_regs_cf_list(&function->impl->body)) {
preserve = false;
progress = true;