ScheduleDAG.cpp revision e07f4c0f48e17594fd39b1151fc18c164aa5b4d1
1//===---- ScheduleDAG.cpp - Implement the ScheduleDAG class ---------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This implements the ScheduleDAG class, which is a base class used by 11// scheduling implementation classes. 12// 13//===----------------------------------------------------------------------===// 14 15#define DEBUG_TYPE "pre-RA-sched" 16#include "llvm/CodeGen/ScheduleDAG.h" 17#include "llvm/Target/TargetMachine.h" 18#include "llvm/Target/TargetInstrInfo.h" 19#include "llvm/Target/TargetRegisterInfo.h" 20#include "llvm/Support/Debug.h" 21#include <climits> 22using namespace llvm; 23 24ScheduleDAG::ScheduleDAG(SelectionDAG *dag, MachineBasicBlock *bb, 25 const TargetMachine &tm) 26 : DAG(dag), BB(bb), TM(tm), MRI(BB->getParent()->getRegInfo()) { 27 TII = TM.getInstrInfo(); 28 MF = BB->getParent(); 29 TRI = TM.getRegisterInfo(); 30 TLI = TM.getTargetLowering(); 31 ConstPool = MF->getConstantPool(); 32} 33 34ScheduleDAG::~ScheduleDAG() {} 35 36/// CalculateDepths - compute depths using algorithms for the longest 37/// paths in the DAG 38void ScheduleDAG::CalculateDepths() { 39 unsigned DAGSize = SUnits.size(); 40 std::vector<SUnit*> WorkList; 41 WorkList.reserve(DAGSize); 42 43 // Initialize the data structures 44 for (unsigned i = 0, e = DAGSize; i != e; ++i) { 45 SUnit *SU = &SUnits[i]; 46 unsigned Degree = SU->Preds.size(); 47 // Temporarily use the Depth field as scratch space for the degree count. 48 SU->Depth = Degree; 49 50 // Is it a node without dependencies? 51 if (Degree == 0) { 52 assert(SU->Preds.empty() && "SUnit should have no predecessors"); 53 // Collect leaf nodes 54 WorkList.push_back(SU); 55 } 56 } 57 58 // Process nodes in the topological order 59 while (!WorkList.empty()) { 60 SUnit *SU = WorkList.back(); 61 WorkList.pop_back(); 62 unsigned SUDepth = 0; 63 64 // Use dynamic programming: 65 // When current node is being processed, all of its dependencies 66 // are already processed. 67 // So, just iterate over all predecessors and take the longest path 68 for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end(); 69 I != E; ++I) { 70 unsigned PredDepth = I->Dep->Depth; 71 if (PredDepth+1 > SUDepth) { 72 SUDepth = PredDepth + 1; 73 } 74 } 75 76 SU->Depth = SUDepth; 77 78 // Update degrees of all nodes depending on current SUnit 79 for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end(); 80 I != E; ++I) { 81 SUnit *SU = I->Dep; 82 if (!--SU->Depth) 83 // If all dependencies of the node are processed already, 84 // then the longest path for the node can be computed now 85 WorkList.push_back(SU); 86 } 87 } 88} 89 90/// CalculateHeights - compute heights using algorithms for the longest 91/// paths in the DAG 92void ScheduleDAG::CalculateHeights() { 93 unsigned DAGSize = SUnits.size(); 94 std::vector<SUnit*> WorkList; 95 WorkList.reserve(DAGSize); 96 97 // Initialize the data structures 98 for (unsigned i = 0, e = DAGSize; i != e; ++i) { 99 SUnit *SU = &SUnits[i]; 100 unsigned Degree = SU->Succs.size(); 101 // Temporarily use the Height field as scratch space for the degree count. 102 SU->Height = Degree; 103 104 // Is it a node without dependencies? 105 if (Degree == 0) { 106 assert(SU->Succs.empty() && "Something wrong"); 107 assert(WorkList.empty() && "Should be empty"); 108 // Collect leaf nodes 109 WorkList.push_back(SU); 110 } 111 } 112 113 // Process nodes in the topological order 114 while (!WorkList.empty()) { 115 SUnit *SU = WorkList.back(); 116 WorkList.pop_back(); 117 unsigned SUHeight = 0; 118 119 // Use dynamic programming: 120 // When current node is being processed, all of its dependencies 121 // are already processed. 122 // So, just iterate over all successors and take the longest path 123 for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end(); 124 I != E; ++I) { 125 unsigned SuccHeight = I->Dep->Height; 126 if (SuccHeight+1 > SUHeight) { 127 SUHeight = SuccHeight + 1; 128 } 129 } 130 131 SU->Height = SUHeight; 132 133 // Update degrees of all nodes depending on current SUnit 134 for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end(); 135 I != E; ++I) { 136 SUnit *SU = I->Dep; 137 if (!--SU->Height) 138 // If all dependencies of the node are processed already, 139 // then the longest path for the node can be computed now 140 WorkList.push_back(SU); 141 } 142 } 143} 144 145/// dump - dump the schedule. 146void ScheduleDAG::dumpSchedule() const { 147 for (unsigned i = 0, e = Sequence.size(); i != e; i++) { 148 if (SUnit *SU = Sequence[i]) 149 SU->dump(this); 150 else 151 cerr << "**** NOOP ****\n"; 152 } 153} 154 155 156/// Run - perform scheduling. 157/// 158void ScheduleDAG::Run() { 159 Schedule(); 160 161 DOUT << "*** Final schedule ***\n"; 162 DEBUG(dumpSchedule()); 163 DOUT << "\n"; 164} 165 166/// SUnit - Scheduling unit. It's an wrapper around either a single SDNode or 167/// a group of nodes flagged together. 168void SUnit::dump(const ScheduleDAG *G) const { 169 cerr << "SU(" << NodeNum << "): "; 170 G->dumpNode(this); 171} 172 173void SUnit::dumpAll(const ScheduleDAG *G) const { 174 dump(G); 175 176 cerr << " # preds left : " << NumPredsLeft << "\n"; 177 cerr << " # succs left : " << NumSuccsLeft << "\n"; 178 cerr << " Latency : " << Latency << "\n"; 179 cerr << " Depth : " << Depth << "\n"; 180 cerr << " Height : " << Height << "\n"; 181 182 if (Preds.size() != 0) { 183 cerr << " Predecessors:\n"; 184 for (SUnit::const_succ_iterator I = Preds.begin(), E = Preds.end(); 185 I != E; ++I) { 186 if (I->isCtrl) 187 cerr << " ch #"; 188 else 189 cerr << " val #"; 190 cerr << I->Dep << " - SU(" << I->Dep->NodeNum << ")"; 191 if (I->isArtificial) 192 cerr << " *"; 193 cerr << "\n"; 194 } 195 } 196 if (Succs.size() != 0) { 197 cerr << " Successors:\n"; 198 for (SUnit::const_succ_iterator I = Succs.begin(), E = Succs.end(); 199 I != E; ++I) { 200 if (I->isCtrl) 201 cerr << " ch #"; 202 else 203 cerr << " val #"; 204 cerr << I->Dep << " - SU(" << I->Dep->NodeNum << ")"; 205 if (I->isArtificial) 206 cerr << " *"; 207 cerr << "\n"; 208 } 209 } 210 cerr << "\n"; 211} 212 213#ifndef NDEBUG 214/// VerifySchedule - Verify that all SUnits were scheduled and that 215/// their state is consistent. 216/// 217void ScheduleDAG::VerifySchedule(bool isBottomUp) { 218 bool AnyNotSched = false; 219 unsigned DeadNodes = 0; 220 unsigned Noops = 0; 221 for (unsigned i = 0, e = SUnits.size(); i != e; ++i) { 222 if (!SUnits[i].isScheduled) { 223 if (SUnits[i].NumPreds == 0 && SUnits[i].NumSuccs == 0) { 224 ++DeadNodes; 225 continue; 226 } 227 if (!AnyNotSched) 228 cerr << "*** Scheduling failed! ***\n"; 229 SUnits[i].dump(this); 230 cerr << "has not been scheduled!\n"; 231 AnyNotSched = true; 232 } 233 if (SUnits[i].isScheduled && SUnits[i].Cycle > (unsigned)INT_MAX) { 234 if (!AnyNotSched) 235 cerr << "*** Scheduling failed! ***\n"; 236 SUnits[i].dump(this); 237 cerr << "has an unexpected Cycle value!\n"; 238 AnyNotSched = true; 239 } 240 if (isBottomUp) { 241 if (SUnits[i].NumSuccsLeft != 0) { 242 if (!AnyNotSched) 243 cerr << "*** Scheduling failed! ***\n"; 244 SUnits[i].dump(this); 245 cerr << "has successors left!\n"; 246 AnyNotSched = true; 247 } 248 } else { 249 if (SUnits[i].NumPredsLeft != 0) { 250 if (!AnyNotSched) 251 cerr << "*** Scheduling failed! ***\n"; 252 SUnits[i].dump(this); 253 cerr << "has predecessors left!\n"; 254 AnyNotSched = true; 255 } 256 } 257 } 258 for (unsigned i = 0, e = Sequence.size(); i != e; ++i) 259 if (!Sequence[i]) 260 ++Noops; 261 assert(!AnyNotSched); 262 assert(Sequence.size() + DeadNodes - Noops == SUnits.size() && 263 "The number of nodes scheduled doesn't match the expected number!"); 264} 265#endif 266 267/// InitDAGTopologicalSorting - create the initial topological 268/// ordering from the DAG to be scheduled. 269/// 270/// The idea of the algorithm is taken from 271/// "Online algorithms for managing the topological order of 272/// a directed acyclic graph" by David J. Pearce and Paul H.J. Kelly 273/// This is the MNR algorithm, which was first introduced by 274/// A. Marchetti-Spaccamela, U. Nanni and H. Rohnert in 275/// "Maintaining a topological order under edge insertions". 276/// 277/// Short description of the algorithm: 278/// 279/// Topological ordering, ord, of a DAG maps each node to a topological 280/// index so that for all edges X->Y it is the case that ord(X) < ord(Y). 281/// 282/// This means that if there is a path from the node X to the node Z, 283/// then ord(X) < ord(Z). 284/// 285/// This property can be used to check for reachability of nodes: 286/// if Z is reachable from X, then an insertion of the edge Z->X would 287/// create a cycle. 288/// 289/// The algorithm first computes a topological ordering for the DAG by 290/// initializing the Index2Node and Node2Index arrays and then tries to keep 291/// the ordering up-to-date after edge insertions by reordering the DAG. 292/// 293/// On insertion of the edge X->Y, the algorithm first marks by calling DFS 294/// the nodes reachable from Y, and then shifts them using Shift to lie 295/// immediately after X in Index2Node. 296void ScheduleDAGTopologicalSort::InitDAGTopologicalSorting() { 297 unsigned DAGSize = SUnits.size(); 298 std::vector<SUnit*> WorkList; 299 WorkList.reserve(DAGSize); 300 301 Index2Node.resize(DAGSize); 302 Node2Index.resize(DAGSize); 303 304 // Initialize the data structures. 305 for (unsigned i = 0, e = DAGSize; i != e; ++i) { 306 SUnit *SU = &SUnits[i]; 307 int NodeNum = SU->NodeNum; 308 unsigned Degree = SU->Succs.size(); 309 // Temporarily use the Node2Index array as scratch space for degree counts. 310 Node2Index[NodeNum] = Degree; 311 312 // Is it a node without dependencies? 313 if (Degree == 0) { 314 assert(SU->Succs.empty() && "SUnit should have no successors"); 315 // Collect leaf nodes. 316 WorkList.push_back(SU); 317 } 318 } 319 320 int Id = DAGSize; 321 while (!WorkList.empty()) { 322 SUnit *SU = WorkList.back(); 323 WorkList.pop_back(); 324 Allocate(SU->NodeNum, --Id); 325 for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end(); 326 I != E; ++I) { 327 SUnit *SU = I->Dep; 328 if (!--Node2Index[SU->NodeNum]) 329 // If all dependencies of the node are processed already, 330 // then the node can be computed now. 331 WorkList.push_back(SU); 332 } 333 } 334 335 Visited.resize(DAGSize); 336 337#ifndef NDEBUG 338 // Check correctness of the ordering 339 for (unsigned i = 0, e = DAGSize; i != e; ++i) { 340 SUnit *SU = &SUnits[i]; 341 for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end(); 342 I != E; ++I) { 343 assert(Node2Index[SU->NodeNum] > Node2Index[I->Dep->NodeNum] && 344 "Wrong topological sorting"); 345 } 346 } 347#endif 348} 349 350/// AddPred - Updates the topological ordering to accomodate an edge 351/// to be added from SUnit X to SUnit Y. 352void ScheduleDAGTopologicalSort::AddPred(SUnit *Y, SUnit *X) { 353 int UpperBound, LowerBound; 354 LowerBound = Node2Index[Y->NodeNum]; 355 UpperBound = Node2Index[X->NodeNum]; 356 bool HasLoop = false; 357 // Is Ord(X) < Ord(Y) ? 358 if (LowerBound < UpperBound) { 359 // Update the topological order. 360 Visited.reset(); 361 DFS(Y, UpperBound, HasLoop); 362 assert(!HasLoop && "Inserted edge creates a loop!"); 363 // Recompute topological indexes. 364 Shift(Visited, LowerBound, UpperBound); 365 } 366} 367 368/// RemovePred - Updates the topological ordering to accomodate an 369/// an edge to be removed from the specified node N from the predecessors 370/// of the current node M. 371void ScheduleDAGTopologicalSort::RemovePred(SUnit *M, SUnit *N) { 372 // InitDAGTopologicalSorting(); 373} 374 375/// DFS - Make a DFS traversal to mark all nodes reachable from SU and mark 376/// all nodes affected by the edge insertion. These nodes will later get new 377/// topological indexes by means of the Shift method. 378void ScheduleDAGTopologicalSort::DFS(const SUnit *SU, int UpperBound, 379 bool& HasLoop) { 380 std::vector<const SUnit*> WorkList; 381 WorkList.reserve(SUnits.size()); 382 383 WorkList.push_back(SU); 384 while (!WorkList.empty()) { 385 SU = WorkList.back(); 386 WorkList.pop_back(); 387 Visited.set(SU->NodeNum); 388 for (int I = SU->Succs.size()-1; I >= 0; --I) { 389 int s = SU->Succs[I].Dep->NodeNum; 390 if (Node2Index[s] == UpperBound) { 391 HasLoop = true; 392 return; 393 } 394 // Visit successors if not already and in affected region. 395 if (!Visited.test(s) && Node2Index[s] < UpperBound) { 396 WorkList.push_back(SU->Succs[I].Dep); 397 } 398 } 399 } 400} 401 402/// Shift - Renumber the nodes so that the topological ordering is 403/// preserved. 404void ScheduleDAGTopologicalSort::Shift(BitVector& Visited, int LowerBound, 405 int UpperBound) { 406 std::vector<int> L; 407 int shift = 0; 408 int i; 409 410 for (i = LowerBound; i <= UpperBound; ++i) { 411 // w is node at topological index i. 412 int w = Index2Node[i]; 413 if (Visited.test(w)) { 414 // Unmark. 415 Visited.reset(w); 416 L.push_back(w); 417 shift = shift + 1; 418 } else { 419 Allocate(w, i - shift); 420 } 421 } 422 423 for (unsigned j = 0; j < L.size(); ++j) { 424 Allocate(L[j], i - shift); 425 i = i + 1; 426 } 427} 428 429 430/// WillCreateCycle - Returns true if adding an edge from SU to TargetSU will 431/// create a cycle. 432bool ScheduleDAGTopologicalSort::WillCreateCycle(SUnit *SU, SUnit *TargetSU) { 433 if (IsReachable(TargetSU, SU)) 434 return true; 435 for (SUnit::pred_iterator I = SU->Preds.begin(), E = SU->Preds.end(); 436 I != E; ++I) 437 if (I->Cost < 0 && IsReachable(TargetSU, I->Dep)) 438 return true; 439 return false; 440} 441 442/// IsReachable - Checks if SU is reachable from TargetSU. 443bool ScheduleDAGTopologicalSort::IsReachable(const SUnit *SU, 444 const SUnit *TargetSU) { 445 // If insertion of the edge SU->TargetSU would create a cycle 446 // then there is a path from TargetSU to SU. 447 int UpperBound, LowerBound; 448 LowerBound = Node2Index[TargetSU->NodeNum]; 449 UpperBound = Node2Index[SU->NodeNum]; 450 bool HasLoop = false; 451 // Is Ord(TargetSU) < Ord(SU) ? 452 if (LowerBound < UpperBound) { 453 Visited.reset(); 454 // There may be a path from TargetSU to SU. Check for it. 455 DFS(TargetSU, UpperBound, HasLoop); 456 } 457 return HasLoop; 458} 459 460/// Allocate - assign the topological index to the node n. 461void ScheduleDAGTopologicalSort::Allocate(int n, int index) { 462 Node2Index[n] = index; 463 Index2Node[index] = n; 464} 465 466ScheduleDAGTopologicalSort::ScheduleDAGTopologicalSort( 467 std::vector<SUnit> &sunits) 468 : SUnits(sunits) {} 469