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
35namespace aco {
36namespace {
37
38struct dce_ctx {
39   int current_block;
40   std::vector<uint16_t> uses;
41   std::vector<std::vector<bool>> live;
42
43   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
52void
53process_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
83bool
84is_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
94std::vector<uint16_t>
95dead_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