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/*
* Copyright © 2024 Collabora, Ltd.
* SPDX-License-Identifier: MIT
*/
#include "nir.h"
#include "nir_builder.h"
static bool
nir_lower_terminate_cf_list(nir_builder *b, struct exec_list *cf_list)
{
bool progress = false;
foreach_list_typed_safe(nir_cf_node, node, node, cf_list) {
switch (node->type) {
case nir_cf_node_block: {
nir_block *block = nir_cf_node_as_block(node);
nir_foreach_instr_safe(instr, block) {
if (instr->type != nir_instr_type_intrinsic)
continue;
nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
switch (intrin->intrinsic) {
case nir_intrinsic_terminate: {
/* Everything after the terminate is dead */
nir_cf_list dead_cf;
nir_cf_extract(&dead_cf, nir_after_instr(&intrin->instr),
nir_after_cf_list(cf_list));
nir_cf_delete(&dead_cf);
intrin->intrinsic = nir_intrinsic_demote;
b->cursor = nir_after_instr(&intrin->instr);
nir_jump(b, nir_jump_halt);
/* We just removed the remainder of this list of CF nodes.
* It's not safe to continue iterating.
*/
return true;
}
case nir_intrinsic_terminate_if:
b->cursor = nir_before_instr(&intrin->instr);
nir_push_if(b, intrin->src[0].ssa);
{
nir_demote(b);
nir_jump(b, nir_jump_halt);
}
nir_instr_remove(&intrin->instr);
progress = true;
break;
default:
break;
}
}
break;
}
case nir_cf_node_if: {
nir_if *nif = nir_cf_node_as_if(node);
progress |= nir_lower_terminate_cf_list(b, &nif->then_list);
progress |= nir_lower_terminate_cf_list(b, &nif->else_list);
break;
}
case nir_cf_node_loop: {
nir_loop *loop = nir_cf_node_as_loop(node);
progress |= nir_lower_terminate_cf_list(b, &loop->body);
progress |= nir_lower_terminate_cf_list(b, &loop->continue_list);
break;
}
default:
UNREACHABLE("Unknown CF node type");
}
}
return progress;
}
static bool
nir_lower_terminate_impl(nir_function_impl *impl)
{
nir_builder b = nir_builder_create(impl);
bool progress = nir_lower_terminate_cf_list(&b, &impl->body);
return nir_progress(progress, impl, nir_metadata_none);
}
/** Lowers nir_intrinsic_terminate to demote + halt
*
* The semantics of nir_intrinsic_terminate require that threads immediately
* exit. In SPIR-V, terminate is branch instruction even though it's only an
* intrinsic in NIR. This pass lowers terminate to demote + halt. Since halt
* is a jump instruction in NIR, this restores those semantics and NIR can
* reason about dead threads after a halt. It allows lets back-ends to only
* implement nir_intrinsic_demote as long as they also implement nir_jump_halt.
*/
bool
nir_lower_terminate_to_demote(nir_shader *nir)
{
bool progress = false;
nir_foreach_function_impl(impl, nir) {
if (nir_lower_terminate_impl(impl))
progress = true;
}
return progress;
}
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