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/*
* Copyright 2018 Collabora Ltd.
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* on the rights to use, copy, modify, merge, publish, distribute, sub
* license, and/or sell copies of the Software, and to permit persons to whom
* the Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice (including the next
* paragraph) shall be included in all copies or substantial portions of the
* Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL
* THE AUTHOR(S) AND/OR THEIR SUPPLIERS BE LIABLE FOR ANY CLAIM,
* DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
* OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
* USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
#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)
{
nir_lower_discard_if_options options = *(nir_lower_discard_if_options *)cb_data;
switch (instr->intrinsic) {
case nir_intrinsic_demote_if:
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;
default:
return false;
}
b->cursor = nir_before_instr(&instr->instr);
nir_if *if_stmt = nir_push_if(b, instr->src[0].ssa);
switch (instr->intrinsic) {
case nir_intrinsic_demote_if:
nir_demote(b);
break;
case nir_intrinsic_terminate_if:
nir_terminate(b);
break;
default:
UNREACHABLE("bad intrinsic");
}
nir_pop_if(b, if_stmt);
nir_instr_remove(&instr->instr);
return true;
/* a shader like this (shaders@glsl-fs-discard-04):
uniform int j, k;
void main()
{
for (int i = 0; i < j; i++) {
if (i > k)
continue;
discard;
}
gl_FragColor = vec4(0.0, 1.0, 0.0, 0.0);
}
will generate nir like:
loop {
//snip
if ssa_11 {
block block_5:
/ preds: block_4 /
vec1 32 ssa_17 = iadd ssa_50, ssa_31
/ succs: block_7 /
} else {
block block_6:
/ preds: block_4 /
intrinsic terminate () () <-- not last instruction
vec1 32 ssa_23 = iadd ssa_50, ssa_31 <-- dead code loop itr increment
/ succs: block_7 /
}
//snip
}
which means that we can't assert like this:
assert(instr->intrinsic != nir_intrinsic_terminate ||
nir_block_last_instr(instr->instr.block) == &instr->instr);
and it's unnecessary anyway since later optimizations will dce the
instructions following the discard
*/
return false;
}
bool
nir_lower_discard_if(nir_shader *shader, nir_lower_discard_if_options options)
{
return nir_shader_intrinsics_pass(shader,
lower_discard_if,
nir_metadata_none,
&options);
}
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