1// Copyright 2012 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/mips/lithium-gap-resolver-mips.h"
6
7#include "src/crankshaft/mips/lithium-codegen-mips.h"
8
9namespace v8 {
10namespace internal {
11
12LGapResolver::LGapResolver(LCodeGen* owner)
13    : cgen_(owner),
14      moves_(32, owner->zone()),
15      root_index_(0),
16      in_cycle_(false),
17      saved_destination_(NULL) {}
18
19
20void LGapResolver::Resolve(LParallelMove* parallel_move) {
21  DCHECK(moves_.is_empty());
22  // Build up a worklist of moves.
23  BuildInitialMoveList(parallel_move);
24
25  for (int i = 0; i < moves_.length(); ++i) {
26    LMoveOperands move = moves_[i];
27    // Skip constants to perform them last.  They don't block other moves
28    // and skipping such moves with register destinations keeps those
29    // registers free for the whole algorithm.
30    if (!move.IsEliminated() && !move.source()->IsConstantOperand()) {
31      root_index_ = i;  // Any cycle is found when by reaching this move again.
32      PerformMove(i);
33      if (in_cycle_) {
34        RestoreValue();
35      }
36    }
37  }
38
39  // Perform the moves with constant sources.
40  for (int i = 0; i < moves_.length(); ++i) {
41    if (!moves_[i].IsEliminated()) {
42      DCHECK(moves_[i].source()->IsConstantOperand());
43      EmitMove(i);
44    }
45  }
46
47  moves_.Rewind(0);
48}
49
50
51void LGapResolver::BuildInitialMoveList(LParallelMove* parallel_move) {
52  // Perform a linear sweep of the moves to add them to the initial list of
53  // moves to perform, ignoring any move that is redundant (the source is
54  // the same as the destination, the destination is ignored and
55  // unallocated, or the move was already eliminated).
56  const ZoneList<LMoveOperands>* moves = parallel_move->move_operands();
57  for (int i = 0; i < moves->length(); ++i) {
58    LMoveOperands move = moves->at(i);
59    if (!move.IsRedundant()) moves_.Add(move, cgen_->zone());
60  }
61  Verify();
62}
63
64
65void LGapResolver::PerformMove(int index) {
66  // Each call to this function performs a move and deletes it from the move
67  // graph.  We first recursively perform any move blocking this one.  We
68  // mark a move as "pending" on entry to PerformMove in order to detect
69  // cycles in the move graph.
70
71  // We can only find a cycle, when doing a depth-first traversal of moves,
72  // be encountering the starting move again. So by spilling the source of
73  // the starting move, we break the cycle.  All moves are then unblocked,
74  // and the starting move is completed by writing the spilled value to
75  // its destination.  All other moves from the spilled source have been
76  // completed prior to breaking the cycle.
77  // An additional complication is that moves to MemOperands with large
78  // offsets (more than 1K or 4K) require us to spill this spilled value to
79  // the stack, to free up the register.
80  DCHECK(!moves_[index].IsPending());
81  DCHECK(!moves_[index].IsRedundant());
82
83  // Clear this move's destination to indicate a pending move.  The actual
84  // destination is saved in a stack allocated local.  Multiple moves can
85  // be pending because this function is recursive.
86  DCHECK(moves_[index].source() != NULL);  // Or else it will look eliminated.
87  LOperand* destination = moves_[index].destination();
88  moves_[index].set_destination(NULL);
89
90  // Perform a depth-first traversal of the move graph to resolve
91  // dependencies.  Any unperformed, unpending move with a source the same
92  // as this one's destination blocks this one so recursively perform all
93  // such moves.
94  for (int i = 0; i < moves_.length(); ++i) {
95    LMoveOperands other_move = moves_[i];
96    if (other_move.Blocks(destination) && !other_move.IsPending()) {
97      PerformMove(i);
98      // If there is a blocking, pending move it must be moves_[root_index_]
99      // and all other moves with the same source as moves_[root_index_] are
100      // sucessfully executed (because they are cycle-free) by this loop.
101    }
102  }
103
104  // We are about to resolve this move and don't need it marked as
105  // pending, so restore its destination.
106  moves_[index].set_destination(destination);
107
108  // The move may be blocked on a pending move, which must be the starting move.
109  // In this case, we have a cycle, and we save the source of this move to
110  // a scratch register to break it.
111  LMoveOperands other_move = moves_[root_index_];
112  if (other_move.Blocks(destination)) {
113    DCHECK(other_move.IsPending());
114    BreakCycle(index);
115    return;
116  }
117
118  // This move is no longer blocked.
119  EmitMove(index);
120}
121
122
123void LGapResolver::Verify() {
124#ifdef ENABLE_SLOW_DCHECKS
125  // No operand should be the destination for more than one move.
126  for (int i = 0; i < moves_.length(); ++i) {
127    LOperand* destination = moves_[i].destination();
128    for (int j = i + 1; j < moves_.length(); ++j) {
129      SLOW_DCHECK(!destination->Equals(moves_[j].destination()));
130    }
131  }
132#endif
133}
134
135#define __ ACCESS_MASM(cgen_->masm())
136
137void LGapResolver::BreakCycle(int index) {
138  // We save in a register the value that should end up in the source of
139  // moves_[root_index].  After performing all moves in the tree rooted
140  // in that move, we save the value to that source.
141  DCHECK(moves_[index].destination()->Equals(moves_[root_index_].source()));
142  DCHECK(!in_cycle_);
143  in_cycle_ = true;
144  LOperand* source = moves_[index].source();
145  saved_destination_ = moves_[index].destination();
146  if (source->IsRegister()) {
147    __ mov(kLithiumScratchReg, cgen_->ToRegister(source));
148  } else if (source->IsStackSlot()) {
149    __ lw(kLithiumScratchReg, cgen_->ToMemOperand(source));
150  } else if (source->IsDoubleRegister()) {
151    __ mov_d(kLithiumScratchDouble, cgen_->ToDoubleRegister(source));
152  } else if (source->IsDoubleStackSlot()) {
153    __ ldc1(kLithiumScratchDouble, cgen_->ToMemOperand(source));
154  } else {
155    UNREACHABLE();
156  }
157  // This move will be done by restoring the saved value to the destination.
158  moves_[index].Eliminate();
159}
160
161
162void LGapResolver::RestoreValue() {
163  DCHECK(in_cycle_);
164  DCHECK(saved_destination_ != NULL);
165
166  // Spilled value is in kLithiumScratchReg or kLithiumScratchDouble.
167  if (saved_destination_->IsRegister()) {
168    __ mov(cgen_->ToRegister(saved_destination_), kLithiumScratchReg);
169  } else if (saved_destination_->IsStackSlot()) {
170    __ sw(kLithiumScratchReg, cgen_->ToMemOperand(saved_destination_));
171  } else if (saved_destination_->IsDoubleRegister()) {
172    __ mov_d(cgen_->ToDoubleRegister(saved_destination_),
173            kLithiumScratchDouble);
174  } else if (saved_destination_->IsDoubleStackSlot()) {
175    __ sdc1(kLithiumScratchDouble,
176            cgen_->ToMemOperand(saved_destination_));
177  } else {
178    UNREACHABLE();
179  }
180
181  in_cycle_ = false;
182  saved_destination_ = NULL;
183}
184
185
186void LGapResolver::EmitMove(int index) {
187  LOperand* source = moves_[index].source();
188  LOperand* destination = moves_[index].destination();
189
190  // Dispatch on the source and destination operand kinds.  Not all
191  // combinations are possible.
192
193  if (source->IsRegister()) {
194    Register source_register = cgen_->ToRegister(source);
195    if (destination->IsRegister()) {
196      __ mov(cgen_->ToRegister(destination), source_register);
197    } else {
198      DCHECK(destination->IsStackSlot());
199      __ sw(source_register, cgen_->ToMemOperand(destination));
200    }
201  } else if (source->IsStackSlot()) {
202    MemOperand source_operand = cgen_->ToMemOperand(source);
203    if (destination->IsRegister()) {
204      __ lw(cgen_->ToRegister(destination), source_operand);
205    } else {
206      DCHECK(destination->IsStackSlot());
207      MemOperand destination_operand = cgen_->ToMemOperand(destination);
208      if (in_cycle_) {
209        if (!destination_operand.OffsetIsInt16Encodable()) {
210          // 'at' is overwritten while saving the value to the destination.
211          // Therefore we can't use 'at'.  It is OK if the read from the source
212          // destroys 'at', since that happens before the value is read.
213          // This uses only a single reg of the double reg-pair.
214          __ lwc1(kLithiumScratchDouble, source_operand);
215          __ swc1(kLithiumScratchDouble, destination_operand);
216        } else {
217          __ lw(at, source_operand);
218          __ sw(at, destination_operand);
219        }
220      } else {
221        __ lw(kLithiumScratchReg, source_operand);
222        __ sw(kLithiumScratchReg, destination_operand);
223      }
224    }
225
226  } else if (source->IsConstantOperand()) {
227    LConstantOperand* constant_source = LConstantOperand::cast(source);
228    if (destination->IsRegister()) {
229      Register dst = cgen_->ToRegister(destination);
230      Representation r = cgen_->IsSmi(constant_source)
231          ? Representation::Smi() : Representation::Integer32();
232      if (cgen_->IsInteger32(constant_source)) {
233        __ li(dst, Operand(cgen_->ToRepresentation(constant_source, r)));
234      } else {
235        __ li(dst, cgen_->ToHandle(constant_source));
236      }
237    } else if (destination->IsDoubleRegister()) {
238      DoubleRegister result = cgen_->ToDoubleRegister(destination);
239      double v = cgen_->ToDouble(constant_source);
240      __ Move(result, v);
241    } else {
242      DCHECK(destination->IsStackSlot());
243      DCHECK(!in_cycle_);  // Constant moves happen after all cycles are gone.
244      Representation r = cgen_->IsSmi(constant_source)
245          ? Representation::Smi() : Representation::Integer32();
246      if (cgen_->IsInteger32(constant_source)) {
247        __ li(kLithiumScratchReg,
248              Operand(cgen_->ToRepresentation(constant_source, r)));
249      } else {
250        __ li(kLithiumScratchReg, cgen_->ToHandle(constant_source));
251      }
252      __ sw(kLithiumScratchReg, cgen_->ToMemOperand(destination));
253    }
254
255  } else if (source->IsDoubleRegister()) {
256    DoubleRegister source_register = cgen_->ToDoubleRegister(source);
257    if (destination->IsDoubleRegister()) {
258      __ mov_d(cgen_->ToDoubleRegister(destination), source_register);
259    } else {
260      DCHECK(destination->IsDoubleStackSlot());
261      MemOperand destination_operand = cgen_->ToMemOperand(destination);
262      __ sdc1(source_register, destination_operand);
263    }
264
265  } else if (source->IsDoubleStackSlot()) {
266    MemOperand source_operand = cgen_->ToMemOperand(source);
267    if (destination->IsDoubleRegister()) {
268      __ ldc1(cgen_->ToDoubleRegister(destination), source_operand);
269    } else {
270      DCHECK(destination->IsDoubleStackSlot());
271      MemOperand destination_operand = cgen_->ToMemOperand(destination);
272      if (in_cycle_) {
273        // kLithiumScratchDouble was used to break the cycle,
274        // but kLithiumScratchReg is free.
275        MemOperand source_high_operand =
276            cgen_->ToHighMemOperand(source);
277        MemOperand destination_high_operand =
278            cgen_->ToHighMemOperand(destination);
279        __ lw(kLithiumScratchReg, source_operand);
280        __ sw(kLithiumScratchReg, destination_operand);
281        __ lw(kLithiumScratchReg, source_high_operand);
282        __ sw(kLithiumScratchReg, destination_high_operand);
283      } else {
284        __ ldc1(kLithiumScratchDouble, source_operand);
285        __ sdc1(kLithiumScratchDouble, destination_operand);
286      }
287    }
288  } else {
289    UNREACHABLE();
290  }
291
292  moves_[index].Eliminate();
293}
294
295
296#undef __
297
298}  // namespace internal
299}  // namespace v8
300