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aco: optimize boolean phis with uniform selections

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Even though the boolean can be divergent, the control flow can be (at
least partially) uniform. For example, we don't have to create any
s_andn2_b64/s_and_b64/s_or_b64 instructions with this code:
a = ...
loop {
    b = bool_phi a, c
    if (uniform)
        break
    c = ...
}
d = phi c

fossil-db (Navi):
Totals from 5506 (4.05% of 135946) affected shaders:
SGPRs: 605720 -> 604024 (-0.28%)
SpillSGPRs: 52025 -> 51733 (-0.56%)
CodeSize: 65221188 -> 64957808 (-0.40%); split: -0.41%, +0.00%
Instrs: 12637881 -> 12584610 (-0.42%); split: -0.42%, +0.00%

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3388>
This commit is contained in:
Rhys Perry 2020-01-09 16:51:34 +00:00 • committed by Marge Bot
parent f622e80494
commit 9a089baff1
1 changed files with 27 additions and 1 deletions
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28
src/amd/compiler/aco_lower_phis.cpp
View file

@ -35,6 +35,9 @@
namespace aco {
struct ssa_state {
bool checked_preds_for_uniform;
bool all_preds_uniform;
bool needs_init;
uint64_t cur_undef_operands;
@ -152,6 +155,19 @@ void lower_divergent_bool_phi(Program *program, ssa_state *state, Block *block,
{
Builder bld(program);
if (!state->checked_preds_for_uniform) {
state->all_preds_uniform = !(block->kind & block_kind_merge);
for (unsigned pred : block->logical_preds)
state->all_preds_uniform = state->all_preds_uniform && (program->blocks[pred].kind & block_kind_uniform);
state->checked_preds_for_uniform = true;
}
if (state->all_preds_uniform) {
assert(block->logical_preds.size() == block->linear_preds.size());
phi->opcode = aco_opcode::p_linear_phi;
return;
}
state->latest.resize(program->blocks.size());
uint64_t undef_operands = 0;
@ -180,14 +196,23 @@ void lower_divergent_bool_phi(Program *program, ssa_state *state, Block *block,
state->writes[block->logical_preds[i]] = program->allocateId();
}
bool uniform_merge = block->kind & block_kind_loop_header;
for (unsigned i = 0; i < phi->operands.size(); i++) {
Block *pred = &program->blocks[block->logical_preds[i]];
bool need_get_ssa = !uniform_merge;
if (block->kind & block_kind_loop_header && !(pred->kind & block_kind_uniform))
uniform_merge = false;
if (phi->operands[i].isUndefined())
continue;
Operand cur = get_ssa(program, pred->index, state, true);
Operand cur(bld.lm);
if (need_get_ssa)
cur = get_ssa(program, pred->index, state, true);
assert(cur.regClass() == bld.lm);
Temp new_cur = {state->writes.at(pred->index), program->lane_mask};
assert(new_cur.regClass() == bld.lm);
@ -241,6 +266,7 @@ void lower_phis(Program* program)
ssa_state state;
for (Block& block : program->blocks) {
state.checked_preds_for_uniform = false;
state.needs_init = true;
for (aco_ptr<Instruction>& phi : block.instructions) {
if (phi->opcode == aco_opcode::p_phi) {