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aco/lower_phis: optimize loop exit phis 

This optimization works by ensuring that disabled lanes
are zero'd before any merge sequence.

Totals from 6075 (4.05% of 150170) affected shaders: (GFX10.3)
CodeSize: 57913908 -> 57913212 (-0.00%)
Instrs: 11055852 -> 11055678 (-0.00%)
Latency: 438705219 -> 438534652 (-0.04%); split: -0.04%, +0.00%
InvThroughput: 125284101 -> 125251397 (-0.03%); split: -0.03%, +0.00%
Copies: 807388 -> 821035 (+1.69%); split: -0.00%, +1.69%
Branches: 391827 -> 391782 (-0.01%)
PreSGPRs: 574841 -> 574838 (-0.00%)

Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11659>
This commit is contained in:
Daniel Schürmann 2021-06-30 14:21:44 +02:00
parent 207249d2b2
commit ef7d840a70
1 changed files with 31 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

32
src/amd/compiler/aco_lower_phis.cpp
View File

@ -36,6 +36,7 @@ enum class pred_defined : uint8_t {
const_1 = 1,
const_0 = 2,
temp = 3,
zero = 4, /* all disabled lanes are zero'd out */
};
MESA_DEFINE_CPP_ENUM_BITFIELD_OPERATORS(pred_defined);
@ -71,7 +72,8 @@ get_ssa(Program* program, unsigned block_idx, ssa_state* state, bool input)
size_t pred = block.linear_preds.size();
Operand op;
if (block.loop_nest_depth < state->loop_nest_depth) {
op = Operand(program->lane_mask);
/* loop-carried value for loop exit phis */
op = Operand::zero(program->lane_mask.bytes());
} else if (block.loop_nest_depth > state->loop_nest_depth || pred == 1 ||
block.kind & block_kind_loop_exit) {
op = get_ssa(program, block.linear_preds[0], state, false);
@ -160,6 +162,22 @@ build_merge_code(Program* program, ssa_state* state, Block* block, Operand cur)
}
assert(prev.isTemp());
/* simpler sequence in case prev has only zeros in disabled lanes */
if ((defined & pred_defined::zero) == pred_defined::zero) {
if (cur.isConstant()) {
if (!cur.constantValue()) {
bld.copy(dst, prev);
return;
}
cur = Operand(exec, bld.lm);
} else {
cur =
bld.sop2(Builder::s_and, bld.def(bld.lm), bld.def(s1, scc), cur, Operand(exec, bld.lm));
}
bld.sop2(Builder::s_or, dst, bld.def(s1, scc), prev, cur);
return;
}
if (cur.isConstant()) {
if (cur.constantValue())
bld.sop2(Builder::s_or, dst, bld.def(s1, scc), prev, Operand(exec, bld.lm));
@ -208,6 +226,18 @@ init_any_pred_defined(Program* program, ssa_state* state, Block* block, aco_ptr<
state->any_pred_defined[block->index] = pred_defined::undef;
}
/* add dominating zero: this allows to emit simpler merge sequences
* if we can ensure that all disabled lanes are always zero on incoming values */
// TODO: find more occasions where pred_defined::zero is beneficial (e.g. with 2+ temp merges)
if (block->kind & block_kind_loop_exit) {
/* zero the loop-carried variable */
if (program->blocks[start].linear_preds.size() > 1) {
state->any_pred_defined[start] |= pred_defined::zero;
// TODO: emit this zero explicitly
state->any_pred_defined[start - 1] = pred_defined::const_0;
}
}
for (unsigned j = start; j < end; j++) {
if (state->any_pred_defined[j] == pred_defined::undef)
continue;