1 // Copyright 2013 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/crankshaft/hydrogen-uint32-analysis.h"
6
7 namespace v8 {
8 namespace internal {
9
10
IsUnsignedLoad(HLoadKeyed * instr)11 static bool IsUnsignedLoad(HLoadKeyed* instr) {
12 switch (instr->elements_kind()) {
13 case UINT8_ELEMENTS:
14 case UINT16_ELEMENTS:
15 case UINT32_ELEMENTS:
16 case UINT8_CLAMPED_ELEMENTS:
17 return true;
18 default:
19 return false;
20 }
21 }
22
23
IsUint32Operation(HValue * instr)24 static bool IsUint32Operation(HValue* instr) {
25 return instr->IsShr() ||
26 (instr->IsLoadKeyed() && IsUnsignedLoad(HLoadKeyed::cast(instr))) ||
27 (instr->IsInteger32Constant() && instr->GetInteger32Constant() >= 0);
28 }
29
30
IsSafeUint32Use(HValue * val,HValue * use)31 bool HUint32AnalysisPhase::IsSafeUint32Use(HValue* val, HValue* use) {
32 // Operations that operate on bits are safe.
33 if (use->IsBitwise() || use->IsShl() || use->IsSar() || use->IsShr()) {
34 return true;
35 } else if (use->IsSimulate() || use->IsArgumentsObject()) {
36 // Deoptimization has special support for uint32.
37 return true;
38 } else if (use->IsChange()) {
39 // Conversions have special support for uint32.
40 // This DCHECK guards that the conversion in question is actually
41 // implemented. Do not extend the whitelist without adding
42 // support to LChunkBuilder::DoChange().
43 DCHECK(HChange::cast(use)->to().IsDouble() ||
44 HChange::cast(use)->to().IsSmi() ||
45 HChange::cast(use)->to().IsTagged());
46 return true;
47 } else if (use->IsStoreKeyed()) {
48 HStoreKeyed* store = HStoreKeyed::cast(use);
49 if (store->is_fixed_typed_array()) {
50 // Storing a value into an external integer array is a bit level
51 // operation.
52 if (store->value() == val) {
53 // Clamping or a conversion to double should have beed inserted.
54 DCHECK(store->elements_kind() != UINT8_CLAMPED_ELEMENTS);
55 DCHECK(store->elements_kind() != FLOAT32_ELEMENTS);
56 DCHECK(store->elements_kind() != FLOAT64_ELEMENTS);
57 return true;
58 }
59 }
60 } else if (use->IsCompareNumericAndBranch()) {
61 HCompareNumericAndBranch* c = HCompareNumericAndBranch::cast(use);
62 return IsUint32Operation(c->left()) && IsUint32Operation(c->right());
63 }
64
65 return false;
66 }
67
68
69 // Iterate over all uses and verify that they are uint32 safe: either don't
70 // distinguish between int32 and uint32 due to their bitwise nature or
71 // have special support for uint32 values.
72 // Encountered phis are optimistically treated as safe uint32 uses,
73 // marked with kUint32 flag and collected in the phis_ list. A separate
74 // pass will be performed later by UnmarkUnsafePhis to clear kUint32 from
75 // phis that are not actually uint32-safe (it requires fix point iteration).
Uint32UsesAreSafe(HValue * uint32val)76 bool HUint32AnalysisPhase::Uint32UsesAreSafe(HValue* uint32val) {
77 bool collect_phi_uses = false;
78 for (HUseIterator it(uint32val->uses()); !it.Done(); it.Advance()) {
79 HValue* use = it.value();
80
81 if (use->IsPhi()) {
82 if (!use->CheckFlag(HInstruction::kUint32)) {
83 // There is a phi use of this value from a phi that is not yet
84 // collected in phis_ array. Separate pass is required.
85 collect_phi_uses = true;
86 }
87
88 // Optimistically treat phis as uint32 safe.
89 continue;
90 }
91
92 if (!IsSafeUint32Use(uint32val, use)) {
93 return false;
94 }
95 }
96
97 if (collect_phi_uses) {
98 for (HUseIterator it(uint32val->uses()); !it.Done(); it.Advance()) {
99 HValue* use = it.value();
100
101 // There is a phi use of this value from a phi that is not yet
102 // collected in phis_ array. Separate pass is required.
103 if (use->IsPhi() && !use->CheckFlag(HInstruction::kUint32)) {
104 use->SetFlag(HInstruction::kUint32);
105 phis_.Add(HPhi::cast(use), zone());
106 }
107 }
108 }
109
110 return true;
111 }
112
113
114 // Check if all operands to the given phi are marked with kUint32 flag.
CheckPhiOperands(HPhi * phi)115 bool HUint32AnalysisPhase::CheckPhiOperands(HPhi* phi) {
116 if (!phi->CheckFlag(HInstruction::kUint32)) {
117 // This phi is not uint32 safe. No need to check operands.
118 return false;
119 }
120
121 for (int j = 0; j < phi->OperandCount(); j++) {
122 HValue* operand = phi->OperandAt(j);
123 if (!operand->CheckFlag(HInstruction::kUint32)) {
124 // Lazily mark constants that fit into uint32 range with kUint32 flag.
125 if (operand->IsInteger32Constant() &&
126 operand->GetInteger32Constant() >= 0) {
127 operand->SetFlag(HInstruction::kUint32);
128 continue;
129 }
130
131 // This phi is not safe, some operands are not uint32 values.
132 return false;
133 }
134 }
135
136 return true;
137 }
138
139
140 // Remove kUint32 flag from the phi itself and its operands. If any operand
141 // was a phi marked with kUint32 place it into a worklist for
142 // transitive clearing of kUint32 flag.
UnmarkPhi(HPhi * phi,ZoneList<HPhi * > * worklist)143 void HUint32AnalysisPhase::UnmarkPhi(HPhi* phi, ZoneList<HPhi*>* worklist) {
144 phi->ClearFlag(HInstruction::kUint32);
145 for (int j = 0; j < phi->OperandCount(); j++) {
146 HValue* operand = phi->OperandAt(j);
147 if (operand->CheckFlag(HInstruction::kUint32)) {
148 operand->ClearFlag(HInstruction::kUint32);
149 if (operand->IsPhi()) {
150 worklist->Add(HPhi::cast(operand), zone());
151 }
152 }
153 }
154 }
155
156
UnmarkUnsafePhis()157 void HUint32AnalysisPhase::UnmarkUnsafePhis() {
158 // No phis were collected. Nothing to do.
159 if (phis_.length() == 0) return;
160
161 // Worklist used to transitively clear kUint32 from phis that
162 // are used as arguments to other phis.
163 ZoneList<HPhi*> worklist(phis_.length(), zone());
164
165 // Phi can be used as a uint32 value if and only if
166 // all its operands are uint32 values and all its
167 // uses are uint32 safe.
168
169 // Iterate over collected phis and unmark those that
170 // are unsafe. When unmarking phi unmark its operands
171 // and add it to the worklist if it is a phi as well.
172 // Phis that are still marked as safe are shifted down
173 // so that all safe phis form a prefix of the phis_ array.
174 int phi_count = 0;
175 for (int i = 0; i < phis_.length(); i++) {
176 HPhi* phi = phis_[i];
177
178 if (CheckPhiOperands(phi) && Uint32UsesAreSafe(phi)) {
179 phis_[phi_count++] = phi;
180 } else {
181 UnmarkPhi(phi, &worklist);
182 }
183 }
184
185 // Now phis array contains only those phis that have safe
186 // non-phi uses. Start transitively clearing kUint32 flag
187 // from phi operands of discovered non-safe phis until
188 // only safe phis are left.
189 while (!worklist.is_empty()) {
190 while (!worklist.is_empty()) {
191 HPhi* phi = worklist.RemoveLast();
192 UnmarkPhi(phi, &worklist);
193 }
194
195 // Check if any operands to safe phis were unmarked
196 // turning a safe phi into unsafe. The same value
197 // can flow into several phis.
198 int new_phi_count = 0;
199 for (int i = 0; i < phi_count; i++) {
200 HPhi* phi = phis_[i];
201
202 if (CheckPhiOperands(phi)) {
203 phis_[new_phi_count++] = phi;
204 } else {
205 UnmarkPhi(phi, &worklist);
206 }
207 }
208 phi_count = new_phi_count;
209 }
210 }
211
212
Run()213 void HUint32AnalysisPhase::Run() {
214 if (!graph()->has_uint32_instructions()) return;
215
216 ZoneList<HInstruction*>* uint32_instructions = graph()->uint32_instructions();
217 for (int i = 0; i < uint32_instructions->length(); ++i) {
218 // Analyze instruction and mark it with kUint32 if all
219 // its uses are uint32 safe.
220 HInstruction* current = uint32_instructions->at(i);
221 if (current->IsLinked() &&
222 current->representation().IsInteger32() &&
223 Uint32UsesAreSafe(current)) {
224 current->SetFlag(HInstruction::kUint32);
225 }
226 }
227
228 // Some phis might have been optimistically marked with kUint32 flag.
229 // Remove this flag from those phis that are unsafe and propagate
230 // this information transitively potentially clearing kUint32 flag
231 // from some non-phi operations that are used as operands to unsafe phis.
232 UnmarkUnsafePhis();
233 }
234
235
236 } // namespace internal
237 } // namespace v8
238