1 /*
2 * Copyright © 2019 Valve Corporation
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining a
5 * copy of this software and associated documentation files (the "Software"),
6 * to deal in the Software without restriction, including without limitation
7 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
8 * and/or sell copies of the Software, and to permit persons to whom the
9 * Software is furnished to do so, subject to the following conditions:
10 *
11 * The above copyright notice and this permission notice (including the next
12 * paragraph) shall be included in all copies or substantial portions of the
13 * Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
18 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
21 * IN THE SOFTWARE.
22 *
23 */
24
25 #include "aco_ir.h"
26
27 #include <algorithm>
28 #include <vector>
29
30 /*
31 * Implements an analysis pass to determine the number of uses
32 * for each SSA-definition.
33 */
34
35 namespace aco {
36 namespace {
37
38 struct dce_ctx {
39 int current_block;
40 std::vector<uint16_t> uses;
41 std::vector<std::vector<bool>> live;
42
dce_ctxaco::__anon454616f50111::dce_ctx43 dce_ctx(Program* program)
44 : current_block(program->blocks.size() - 1), uses(program->peekAllocationId())
45 {
46 live.reserve(program->blocks.size());
47 for (Block& block : program->blocks)
48 live.emplace_back(block.instructions.size());
49 }
50 };
51
52 void
process_block(dce_ctx & ctx,Block & block)53 process_block(dce_ctx& ctx, Block& block)
54 {
55 std::vector<bool>& live = ctx.live[block.index];
56 assert(live.size() == block.instructions.size());
57 bool process_predecessors = false;
58 for (int idx = block.instructions.size() - 1; idx >= 0; idx--) {
59 if (live[idx])
60 continue;
61
62 aco_ptr<Instruction>& instr = block.instructions[idx];
63 if (!is_dead(ctx.uses, instr.get())) {
64 for (const Operand& op : instr->operands) {
65 if (op.isTemp()) {
66 if (ctx.uses[op.tempId()] == 0)
67 process_predecessors = true;
68 ctx.uses[op.tempId()]++;
69 }
70 }
71 live[idx] = true;
72 }
73 }
74
75 if (process_predecessors) {
76 for (unsigned pred_idx : block.linear_preds)
77 ctx.current_block = std::max(ctx.current_block, (int)pred_idx);
78 }
79 }
80
81 } /* end namespace */
82
83 bool
is_dead(const std::vector<uint16_t> & uses,Instruction * instr)84 is_dead(const std::vector<uint16_t>& uses, Instruction* instr)
85 {
86 if (instr->definitions.empty() || instr->isBranch())
87 return false;
88 if (std::any_of(instr->definitions.begin(), instr->definitions.end(),
89 [&uses](const Definition& def) { return !def.isTemp() || uses[def.tempId()]; }))
90 return false;
91 return !(get_sync_info(instr).semantics & (semantic_volatile | semantic_acqrel));
92 }
93
94 std::vector<uint16_t>
dead_code_analysis(Program * program)95 dead_code_analysis(Program* program)
96 {
97
98 dce_ctx ctx(program);
99
100 while (ctx.current_block >= 0) {
101 unsigned next_block = ctx.current_block--;
102 process_block(ctx, program->blocks[next_block]);
103 }
104
105 /* add one use to exec to prevent startpgm from being removed */
106 aco_ptr<Instruction>& startpgm = program->blocks[0].instructions[0];
107 assert(startpgm->opcode == aco_opcode::p_startpgm);
108 ctx.uses[startpgm->definitions.back().tempId()]++;
109
110 return ctx.uses;
111 }
112
113 } // namespace aco
114