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/v8.h"
6
7#include "src/arm/lithium-codegen-arm.h"
8#include "src/arm/lithium-gap-resolver-arm.h"
9
10namespace v8 {
11namespace internal {
12
13// We use the root register to spill a value while breaking a cycle in parallel
14// moves. We don't need access to roots while resolving the move list and using
15// the root register has two advantages:
16//  - It is not in crankshaft allocatable registers list, so it can't interfere
17//    with any of the moves we are resolving.
18//  - We don't need to push it on the stack, as we can reload it with its value
19//    once we have resolved a cycle.
20#define kSavedValueRegister kRootRegister
21
22
23LGapResolver::LGapResolver(LCodeGen* owner)
24    : cgen_(owner), moves_(32, owner->zone()), root_index_(0), in_cycle_(false),
25      saved_destination_(NULL), need_to_restore_root_(false) { }
26
27
28#define __ ACCESS_MASM(cgen_->masm())
29
30
31void LGapResolver::Resolve(LParallelMove* parallel_move) {
32  DCHECK(moves_.is_empty());
33  // Build up a worklist of moves.
34  BuildInitialMoveList(parallel_move);
35
36  for (int i = 0; i < moves_.length(); ++i) {
37    LMoveOperands move = moves_[i];
38    // Skip constants to perform them last.  They don't block other moves
39    // and skipping such moves with register destinations keeps those
40    // registers free for the whole algorithm.
41    if (!move.IsEliminated() && !move.source()->IsConstantOperand()) {
42      root_index_ = i;  // Any cycle is found when by reaching this move again.
43      PerformMove(i);
44      if (in_cycle_) {
45        RestoreValue();
46      }
47    }
48  }
49
50  // Perform the moves with constant sources.
51  for (int i = 0; i < moves_.length(); ++i) {
52    if (!moves_[i].IsEliminated()) {
53      DCHECK(moves_[i].source()->IsConstantOperand());
54      EmitMove(i);
55    }
56  }
57
58  if (need_to_restore_root_) {
59    DCHECK(kSavedValueRegister.is(kRootRegister));
60    __ InitializeRootRegister();
61    need_to_restore_root_ = false;
62  }
63
64  moves_.Rewind(0);
65}
66
67
68void LGapResolver::BuildInitialMoveList(LParallelMove* parallel_move) {
69  // Perform a linear sweep of the moves to add them to the initial list of
70  // moves to perform, ignoring any move that is redundant (the source is
71  // the same as the destination, the destination is ignored and
72  // unallocated, or the move was already eliminated).
73  const ZoneList<LMoveOperands>* moves = parallel_move->move_operands();
74  for (int i = 0; i < moves->length(); ++i) {
75    LMoveOperands move = moves->at(i);
76    if (!move.IsRedundant()) moves_.Add(move, cgen_->zone());
77  }
78  Verify();
79}
80
81
82void LGapResolver::PerformMove(int index) {
83  // Each call to this function performs a move and deletes it from the move
84  // graph.  We first recursively perform any move blocking this one.  We
85  // mark a move as "pending" on entry to PerformMove in order to detect
86  // cycles in the move graph.
87
88  // We can only find a cycle, when doing a depth-first traversal of moves,
89  // be encountering the starting move again. So by spilling the source of
90  // the starting move, we break the cycle.  All moves are then unblocked,
91  // and the starting move is completed by writing the spilled value to
92  // its destination.  All other moves from the spilled source have been
93  // completed prior to breaking the cycle.
94  // An additional complication is that moves to MemOperands with large
95  // offsets (more than 1K or 4K) require us to spill this spilled value to
96  // the stack, to free up the register.
97  DCHECK(!moves_[index].IsPending());
98  DCHECK(!moves_[index].IsRedundant());
99
100  // Clear this move's destination to indicate a pending move.  The actual
101  // destination is saved in a stack allocated local.  Multiple moves can
102  // be pending because this function is recursive.
103  DCHECK(moves_[index].source() != NULL);  // Or else it will look eliminated.
104  LOperand* destination = moves_[index].destination();
105  moves_[index].set_destination(NULL);
106
107  // Perform a depth-first traversal of the move graph to resolve
108  // dependencies.  Any unperformed, unpending move with a source the same
109  // as this one's destination blocks this one so recursively perform all
110  // such moves.
111  for (int i = 0; i < moves_.length(); ++i) {
112    LMoveOperands other_move = moves_[i];
113    if (other_move.Blocks(destination) && !other_move.IsPending()) {
114      PerformMove(i);
115      // If there is a blocking, pending move it must be moves_[root_index_]
116      // and all other moves with the same source as moves_[root_index_] are
117      // sucessfully executed (because they are cycle-free) by this loop.
118    }
119  }
120
121  // We are about to resolve this move and don't need it marked as
122  // pending, so restore its destination.
123  moves_[index].set_destination(destination);
124
125  // The move may be blocked on a pending move, which must be the starting move.
126  // In this case, we have a cycle, and we save the source of this move to
127  // a scratch register to break it.
128  LMoveOperands other_move = moves_[root_index_];
129  if (other_move.Blocks(destination)) {
130    DCHECK(other_move.IsPending());
131    BreakCycle(index);
132    return;
133  }
134
135  // This move is no longer blocked.
136  EmitMove(index);
137}
138
139
140void LGapResolver::Verify() {
141#ifdef ENABLE_SLOW_DCHECKS
142  // No operand should be the destination for more than one move.
143  for (int i = 0; i < moves_.length(); ++i) {
144    LOperand* destination = moves_[i].destination();
145    for (int j = i + 1; j < moves_.length(); ++j) {
146      SLOW_DCHECK(!destination->Equals(moves_[j].destination()));
147    }
148  }
149#endif
150}
151
152
153void LGapResolver::BreakCycle(int index) {
154  // We save in a register the source of that move and we remember its
155  // destination. Then we mark this move as resolved so the cycle is
156  // broken and we can perform the other moves.
157  DCHECK(moves_[index].destination()->Equals(moves_[root_index_].source()));
158  DCHECK(!in_cycle_);
159  in_cycle_ = true;
160  LOperand* source = moves_[index].source();
161  saved_destination_ = moves_[index].destination();
162  if (source->IsRegister()) {
163    need_to_restore_root_ = true;
164    __ mov(kSavedValueRegister, cgen_->ToRegister(source));
165  } else if (source->IsStackSlot()) {
166    need_to_restore_root_ = true;
167    __ ldr(kSavedValueRegister, cgen_->ToMemOperand(source));
168  } else if (source->IsDoubleRegister()) {
169    __ vmov(kScratchDoubleReg, cgen_->ToDoubleRegister(source));
170  } else if (source->IsDoubleStackSlot()) {
171    __ vldr(kScratchDoubleReg, cgen_->ToMemOperand(source));
172  } else {
173    UNREACHABLE();
174  }
175  // This move will be done by restoring the saved value to the destination.
176  moves_[index].Eliminate();
177}
178
179
180void LGapResolver::RestoreValue() {
181  DCHECK(in_cycle_);
182  DCHECK(saved_destination_ != NULL);
183
184  if (saved_destination_->IsRegister()) {
185    __ mov(cgen_->ToRegister(saved_destination_), kSavedValueRegister);
186  } else if (saved_destination_->IsStackSlot()) {
187    __ str(kSavedValueRegister, cgen_->ToMemOperand(saved_destination_));
188  } else if (saved_destination_->IsDoubleRegister()) {
189    __ vmov(cgen_->ToDoubleRegister(saved_destination_), kScratchDoubleReg);
190  } else if (saved_destination_->IsDoubleStackSlot()) {
191    __ vstr(kScratchDoubleReg, cgen_->ToMemOperand(saved_destination_));
192  } else {
193    UNREACHABLE();
194  }
195
196  in_cycle_ = false;
197  saved_destination_ = NULL;
198}
199
200
201void LGapResolver::EmitMove(int index) {
202  LOperand* source = moves_[index].source();
203  LOperand* destination = moves_[index].destination();
204
205  // Dispatch on the source and destination operand kinds.  Not all
206  // combinations are possible.
207
208  if (source->IsRegister()) {
209    Register source_register = cgen_->ToRegister(source);
210    if (destination->IsRegister()) {
211      __ mov(cgen_->ToRegister(destination), source_register);
212    } else {
213      DCHECK(destination->IsStackSlot());
214      __ str(source_register, cgen_->ToMemOperand(destination));
215    }
216  } else if (source->IsStackSlot()) {
217    MemOperand source_operand = cgen_->ToMemOperand(source);
218    if (destination->IsRegister()) {
219      __ ldr(cgen_->ToRegister(destination), source_operand);
220    } else {
221      DCHECK(destination->IsStackSlot());
222      MemOperand destination_operand = cgen_->ToMemOperand(destination);
223      if (!destination_operand.OffsetIsUint12Encodable()) {
224        // ip is overwritten while saving the value to the destination.
225        // Therefore we can't use ip.  It is OK if the read from the source
226        // destroys ip, since that happens before the value is read.
227        __ vldr(kScratchDoubleReg.low(), source_operand);
228        __ vstr(kScratchDoubleReg.low(), destination_operand);
229      } else {
230        __ ldr(ip, source_operand);
231        __ str(ip, destination_operand);
232      }
233    }
234
235  } else if (source->IsConstantOperand()) {
236    LConstantOperand* constant_source = LConstantOperand::cast(source);
237    if (destination->IsRegister()) {
238      Register dst = cgen_->ToRegister(destination);
239      Representation r = cgen_->IsSmi(constant_source)
240          ? Representation::Smi() : Representation::Integer32();
241      if (cgen_->IsInteger32(constant_source)) {
242        __ mov(dst, Operand(cgen_->ToRepresentation(constant_source, r)));
243      } else {
244        __ Move(dst, cgen_->ToHandle(constant_source));
245      }
246    } else if (destination->IsDoubleRegister()) {
247      DwVfpRegister result = cgen_->ToDoubleRegister(destination);
248      double v = cgen_->ToDouble(constant_source);
249      __ Vmov(result, v, ip);
250    } else {
251      DCHECK(destination->IsStackSlot());
252      DCHECK(!in_cycle_);  // Constant moves happen after all cycles are gone.
253      need_to_restore_root_ = true;
254      Representation r = cgen_->IsSmi(constant_source)
255          ? Representation::Smi() : Representation::Integer32();
256      if (cgen_->IsInteger32(constant_source)) {
257        __ mov(kSavedValueRegister,
258               Operand(cgen_->ToRepresentation(constant_source, r)));
259      } else {
260        __ Move(kSavedValueRegister, cgen_->ToHandle(constant_source));
261      }
262      __ str(kSavedValueRegister, cgen_->ToMemOperand(destination));
263    }
264
265  } else if (source->IsDoubleRegister()) {
266    DwVfpRegister source_register = cgen_->ToDoubleRegister(source);
267    if (destination->IsDoubleRegister()) {
268      __ vmov(cgen_->ToDoubleRegister(destination), source_register);
269    } else {
270      DCHECK(destination->IsDoubleStackSlot());
271      __ vstr(source_register, cgen_->ToMemOperand(destination));
272    }
273
274  } else if (source->IsDoubleStackSlot()) {
275    MemOperand source_operand = cgen_->ToMemOperand(source);
276    if (destination->IsDoubleRegister()) {
277      __ vldr(cgen_->ToDoubleRegister(destination), source_operand);
278    } else {
279      DCHECK(destination->IsDoubleStackSlot());
280      MemOperand destination_operand = cgen_->ToMemOperand(destination);
281      if (in_cycle_) {
282        // kScratchDoubleReg was used to break the cycle.
283        __ vstm(db_w, sp, kScratchDoubleReg, kScratchDoubleReg);
284        __ vldr(kScratchDoubleReg, source_operand);
285        __ vstr(kScratchDoubleReg, destination_operand);
286        __ vldm(ia_w, sp, kScratchDoubleReg, kScratchDoubleReg);
287      } else {
288        __ vldr(kScratchDoubleReg, source_operand);
289        __ vstr(kScratchDoubleReg, destination_operand);
290      }
291    }
292  } else {
293    UNREACHABLE();
294  }
295
296  moves_[index].Eliminate();
297}
298
299
300#undef __
301
302} }  // namespace v8::internal
303