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
7namespace v8 {
8namespace internal {
9
10
11static 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
24static bool IsUint32Operation(HValue* instr) {
25  return instr->IsShr() ||
26      (instr->IsLoadKeyed() && IsUnsignedLoad(HLoadKeyed::cast(instr))) ||
27      (instr->IsInteger32Constant() && instr->GetInteger32Constant() >= 0);
28}
29
30
31bool 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).
76bool 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.
115bool 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.
143void 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
157void 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
213void 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