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nir: add option to move terminate{_if} out of loops

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Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33479>
This commit is contained in:
Daniel Schürmann 2025-02-10 16:01:52 +01:00 • committed by Marge Bot
parent 07ae79d4f9
commit c59356e6a5
2 changed files with 80 additions and 0 deletions
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1
src/compiler/nir/nir.h
View file

@ -5900,6 +5900,7 @@ bool nir_lower_interpolation(nir_shader *shader,
typedef enum {
nir_lower_demote_if_to_cf = (1 << 0),
nir_lower_terminate_if_to_cf = (1 << 1),
nir_move_terminate_out_of_loops = (1 << 2),
} nir_lower_discard_if_options;
bool nir_lower_discard_if(nir_shader *shader, nir_lower_discard_if_options options);

79
src/compiler/nir/nir_lower_discard_if.c
View file

@ -22,8 +22,81 @@
*/
#include "compiler/nir/nir_builder.h"
#include "util/set.h"
#include "nir.h"
/**
* Moves terminate{_if} intrinsics out of loops.
*
* This lowering turns:
*
* loop {
* ...
* terminate_if(cond);
* ...
* }
*
* into:
*
* reg = false
* loop {
* ...
* if (cond) {
* reg = true;
* break;
* }
* ...
* }
* terminate_if(reg);
*/
static bool
move_out_of_loop(nir_builder *b, nir_intrinsic_instr *instr)
{
nir_cf_node *node = instr->instr.block->cf_node.parent;
while (node && node->type != nir_cf_node_loop)
node = node->parent;
if (node == NULL)
return false;
/* Lower the loop to LCSSA form, so that we don't break SSA. */
nir_convert_loop_to_lcssa(nir_cf_node_as_loop(node));
/* Create phi instruction for the terminate condition. */
nir_phi_instr *phi_instr = nir_phi_instr_create(b->shader);
nir_def_init(&phi_instr->instr, &phi_instr->def, 1, 1);
/* Set phi-src to 'false' for existing break conditions. */
b->cursor = nir_before_cf_node(node);
nir_def *false_val = nir_imm_false(b);
nir_block *after_loop = nir_cf_node_cf_tree_next(node);
set_foreach(after_loop->predecessors, entry) {
nir_phi_instr_add_src(phi_instr, (nir_block *)entry->key, false_val);
}
/* Break if terminate. */
b->cursor = nir_instr_remove(&instr->instr);
nir_def *cond = instr->intrinsic == nir_intrinsic_terminate_if
? instr->src[0].ssa
: nir_imm_true(b);
nir_push_if(b, cond);
nir_jump(b, nir_jump_break);
nir_block *break_block = nir_cursor_current_block(b->cursor);
nir_pop_if(b, NULL);
/* Add undef for existing phis and terminate condition for the new phi. */
nir_insert_phi_undef(after_loop, break_block);
nir_phi_instr_add_src(phi_instr, break_block, cond);
/* Insert phi and new terminate instruction. */
b->cursor = nir_after_phis(after_loop);
nir_builder_instr_insert(b, &phi_instr->instr);
nir_terminate_if(b, &phi_instr->def);
return true;
}
static bool
lower_discard_if(nir_builder *b, nir_intrinsic_instr *instr, void *cb_data)
{
@ -34,7 +107,13 @@ lower_discard_if(nir_builder *b, nir_intrinsic_instr *instr, void *cb_data)
if (!(options & nir_lower_demote_if_to_cf))
return false;
break;
case nir_intrinsic_terminate:
return (options & nir_move_terminate_out_of_loops) &&
move_out_of_loop(b, instr);
case nir_intrinsic_terminate_if:
if ((options & nir_move_terminate_out_of_loops) &&
move_out_of_loop(b, instr))
return true;
if (!(options & nir_lower_terminate_if_to_cf))
return false;
break;