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