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Emily Bernierd0a1eb72015-03-24 16:35:39 -04001// Copyright 2014 the V8 project authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#include "src/compiler/move-optimizer.h"
6
7namespace v8 {
8namespace internal {
9namespace compiler {
10
11MoveOptimizer::MoveOptimizer(Zone* local_zone, InstructionSequence* code)
12 : local_zone_(local_zone),
13 code_(code),
14 temp_vector_0_(local_zone),
15 temp_vector_1_(local_zone) {}
16
17
18void MoveOptimizer::Run() {
19 // First smash all consecutive moves into the left most move slot.
20 for (auto* block : code()->instruction_blocks()) {
21 GapInstruction* prev_gap = nullptr;
22 for (int index = block->code_start(); index < block->code_end(); ++index) {
23 auto instr = code()->instructions()[index];
24 if (!instr->IsGapMoves()) {
25 if (instr->IsSourcePosition() || instr->IsNop()) continue;
26 FinalizeMoves(&temp_vector_0_, &temp_vector_1_, prev_gap);
27 prev_gap = nullptr;
28 continue;
29 }
30 auto gap = GapInstruction::cast(instr);
31 // Find first non-empty slot.
32 int i = GapInstruction::FIRST_INNER_POSITION;
33 for (; i <= GapInstruction::LAST_INNER_POSITION; i++) {
34 auto move = gap->parallel_moves()[i];
35 if (move == nullptr) continue;
36 auto move_ops = move->move_operands();
37 auto op = move_ops->begin();
38 for (; op != move_ops->end(); ++op) {
39 if (!op->IsRedundant()) break;
40 }
41 if (op == move_ops->end()) {
42 move_ops->Rewind(0); // Clear this redundant move.
43 } else {
44 break; // Found index of first non-redundant move.
45 }
46 }
47 // Nothing to do here.
48 if (i == GapInstruction::LAST_INNER_POSITION + 1) {
49 if (prev_gap != nullptr) {
50 // Slide prev_gap down so we always know where to look for it.
51 std::swap(prev_gap->parallel_moves()[0], gap->parallel_moves()[0]);
52 prev_gap = gap;
53 }
54 continue;
55 }
56 // Move the first non-empty gap to position 0.
57 std::swap(gap->parallel_moves()[0], gap->parallel_moves()[i]);
58 auto left = gap->parallel_moves()[0];
59 // Compress everything into position 0.
60 for (++i; i <= GapInstruction::LAST_INNER_POSITION; ++i) {
61 auto move = gap->parallel_moves()[i];
62 if (move == nullptr) continue;
63 CompressMoves(&temp_vector_0_, left, move);
64 }
65 if (prev_gap != nullptr) {
66 // Smash left into prev_gap, killing left.
67 auto pred_moves = prev_gap->parallel_moves()[0];
68 CompressMoves(&temp_vector_0_, pred_moves, left);
69 std::swap(prev_gap->parallel_moves()[0], gap->parallel_moves()[0]);
70 }
71 prev_gap = gap;
72 }
73 FinalizeMoves(&temp_vector_0_, &temp_vector_1_, prev_gap);
74 }
75}
76
77
78static MoveOperands* PrepareInsertAfter(ParallelMove* left, MoveOperands* move,
79 Zone* zone) {
80 auto move_ops = left->move_operands();
81 MoveOperands* replacement = nullptr;
82 MoveOperands* to_eliminate = nullptr;
83 for (auto curr = move_ops->begin(); curr != move_ops->end(); ++curr) {
84 if (curr->IsEliminated()) continue;
85 if (curr->destination()->Equals(move->source())) {
86 DCHECK_EQ(nullptr, replacement);
87 replacement = curr;
88 if (to_eliminate != nullptr) break;
89 } else if (curr->destination()->Equals(move->destination())) {
90 DCHECK_EQ(nullptr, to_eliminate);
91 to_eliminate = curr;
92 if (replacement != nullptr) break;
93 }
94 }
95 DCHECK(!(replacement == to_eliminate && replacement != nullptr));
96 if (replacement != nullptr) {
97 auto new_source = new (zone) InstructionOperand(
98 replacement->source()->kind(), replacement->source()->index());
99 move->set_source(new_source);
100 }
101 return to_eliminate;
102}
103
104
105void MoveOptimizer::CompressMoves(MoveOpVector* eliminated, ParallelMove* left,
106 ParallelMove* right) {
107 DCHECK(eliminated->empty());
108 auto move_ops = right->move_operands();
109 // Modify the right moves in place and collect moves that will be killed by
110 // merging the two gaps.
111 for (auto op = move_ops->begin(); op != move_ops->end(); ++op) {
112 if (op->IsRedundant()) continue;
113 MoveOperands* to_eliminate = PrepareInsertAfter(left, op, code_zone());
114 if (to_eliminate != nullptr) {
115 eliminated->push_back(to_eliminate);
116 }
117 }
118 // Eliminate dead moves. Must happen before insertion of new moves as the
119 // contents of eliminated are pointers into a list.
120 for (auto to_eliminate : *eliminated) {
121 to_eliminate->Eliminate();
122 }
123 eliminated->clear();
124 // Add all possibly modified moves from right side.
125 for (auto op = move_ops->begin(); op != move_ops->end(); ++op) {
126 if (op->IsRedundant()) continue;
127 left->move_operands()->Add(*op, code_zone());
128 }
129 // Nuke right.
130 move_ops->Rewind(0);
131}
132
133
134void MoveOptimizer::FinalizeMoves(MoveOpVector* loads, MoveOpVector* new_moves,
135 GapInstruction* gap) {
136 DCHECK(loads->empty());
137 DCHECK(new_moves->empty());
138 if (gap == nullptr) return;
139 // Split multiple loads of the same constant or stack slot off into the second
140 // slot and keep remaining moves in the first slot.
141 auto move_ops = gap->parallel_moves()[0]->move_operands();
142 for (auto move = move_ops->begin(); move != move_ops->end(); ++move) {
143 if (move->IsRedundant()) {
144 move->Eliminate();
145 continue;
146 }
147 if (!(move->source()->IsConstant() || move->source()->IsStackSlot() ||
148 move->source()->IsDoubleStackSlot()))
149 continue;
150 // Search for existing move to this slot.
151 MoveOperands* found = nullptr;
152 for (auto load : *loads) {
153 if (load->source()->Equals(move->source())) {
154 found = load;
155 break;
156 }
157 }
158 // Not found so insert.
159 if (found == nullptr) {
160 loads->push_back(move);
161 // Replace source with copy for later use.
162 auto dest = move->destination();
163 move->set_destination(new (code_zone())
164 InstructionOperand(dest->kind(), dest->index()));
165 continue;
166 }
167 if ((found->destination()->IsStackSlot() ||
168 found->destination()->IsDoubleStackSlot()) &&
169 !(move->destination()->IsStackSlot() ||
170 move->destination()->IsDoubleStackSlot())) {
171 // Found a better source for this load. Smash it in place to affect other
172 // loads that have already been split.
173 InstructionOperand::Kind found_kind = found->destination()->kind();
174 int found_index = found->destination()->index();
175 auto next_dest =
176 new (code_zone()) InstructionOperand(found_kind, found_index);
177 auto dest = move->destination();
178 found->destination()->ConvertTo(dest->kind(), dest->index());
179 move->set_destination(next_dest);
180 }
181 // move from load destination.
182 move->set_source(found->destination());
183 new_moves->push_back(move);
184 }
185 loads->clear();
186 if (new_moves->empty()) return;
187 // Insert all new moves into slot 1.
188 auto slot_1 = gap->GetOrCreateParallelMove(
189 static_cast<GapInstruction::InnerPosition>(1), code_zone());
190 DCHECK(slot_1->move_operands()->is_empty());
191 slot_1->move_operands()->AddBlock(MoveOperands(nullptr, nullptr),
192 static_cast<int>(new_moves->size()),
193 code_zone());
194 auto it = slot_1->move_operands()->begin();
195 for (auto new_move : *new_moves) {
196 std::swap(*new_move, *it);
197 ++it;
198 }
199 DCHECK_EQ(it, slot_1->move_operands()->end());
200 new_moves->clear();
201}
202
203} // namespace compiler
204} // namespace internal
205} // namespace v8