1//===- SparsePropagation.h - Sparse Conditional Property Propagation ------===// 2// 3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4// See https://llvm.org/LICENSE.txt for license information. 5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6// 7//===----------------------------------------------------------------------===// 8// 9// This file implements an abstract sparse conditional propagation algorithm, 10// modeled after SCCP, but with a customizable lattice function. 11// 12//===----------------------------------------------------------------------===// 13 14#ifndef LLVM_ANALYSIS_SPARSEPROPAGATION_H 15#define LLVM_ANALYSIS_SPARSEPROPAGATION_H 16 17#include "llvm/IR/Instructions.h" 18#include "llvm/Support/Debug.h" 19#include <set> 20 21#define DEBUG_TYPE "sparseprop" 22 23namespace llvm { 24 25/// A template for translating between LLVM Values and LatticeKeys. Clients must 26/// provide a specialization of LatticeKeyInfo for their LatticeKey type. 27template <class LatticeKey> struct LatticeKeyInfo { 28 // static inline Value *getValueFromLatticeKey(LatticeKey Key); 29 // static inline LatticeKey getLatticeKeyFromValue(Value *V); 30}; 31 32template <class LatticeKey, class LatticeVal, 33 class KeyInfo = LatticeKeyInfo<LatticeKey>> 34class SparseSolver; 35 36/// AbstractLatticeFunction - This class is implemented by the dataflow instance 37/// to specify what the lattice values are and how they handle merges etc. This 38/// gives the client the power to compute lattice values from instructions, 39/// constants, etc. The current requirement is that lattice values must be 40/// copyable. At the moment, nothing tries to avoid copying. Additionally, 41/// lattice keys must be able to be used as keys of a mapping data structure. 42/// Internally, the generic solver currently uses a DenseMap to map lattice keys 43/// to lattice values. If the lattice key is a non-standard type, a 44/// specialization of DenseMapInfo must be provided. 45template <class LatticeKey, class LatticeVal> class AbstractLatticeFunction { 46private: 47 LatticeVal UndefVal, OverdefinedVal, UntrackedVal; 48 49public: 50 AbstractLatticeFunction(LatticeVal undefVal, LatticeVal overdefinedVal, 51 LatticeVal untrackedVal) { 52 UndefVal = undefVal; 53 OverdefinedVal = overdefinedVal; 54 UntrackedVal = untrackedVal; 55 } 56 57 virtual ~AbstractLatticeFunction() = default; 58 59 LatticeVal getUndefVal() const { return UndefVal; } 60 LatticeVal getOverdefinedVal() const { return OverdefinedVal; } 61 LatticeVal getUntrackedVal() const { return UntrackedVal; } 62 63 /// IsUntrackedValue - If the specified LatticeKey is obviously uninteresting 64 /// to the analysis (i.e., it would always return UntrackedVal), this 65 /// function can return true to avoid pointless work. 66 virtual bool IsUntrackedValue(LatticeKey Key) { return false; } 67 68 /// ComputeLatticeVal - Compute and return a LatticeVal corresponding to the 69 /// given LatticeKey. 70 virtual LatticeVal ComputeLatticeVal(LatticeKey Key) { 71 return getOverdefinedVal(); 72 } 73 74 /// IsSpecialCasedPHI - Given a PHI node, determine whether this PHI node is 75 /// one that the we want to handle through ComputeInstructionState. 76 virtual bool IsSpecialCasedPHI(PHINode *PN) { return false; } 77 78 /// MergeValues - Compute and return the merge of the two specified lattice 79 /// values. Merging should only move one direction down the lattice to 80 /// guarantee convergence (toward overdefined). 81 virtual LatticeVal MergeValues(LatticeVal X, LatticeVal Y) { 82 return getOverdefinedVal(); // always safe, never useful. 83 } 84 85 /// ComputeInstructionState - Compute the LatticeKeys that change as a result 86 /// of executing instruction \p I. Their associated LatticeVals are store in 87 /// \p ChangedValues. 88 virtual void 89 ComputeInstructionState(Instruction &I, 90 DenseMap<LatticeKey, LatticeVal> &ChangedValues, 91 SparseSolver<LatticeKey, LatticeVal> &SS) = 0; 92 93 /// PrintLatticeVal - Render the given LatticeVal to the specified stream. 94 virtual void PrintLatticeVal(LatticeVal LV, raw_ostream &OS); 95 96 /// PrintLatticeKey - Render the given LatticeKey to the specified stream. 97 virtual void PrintLatticeKey(LatticeKey Key, raw_ostream &OS); 98 99 /// GetValueFromLatticeVal - If the given LatticeVal is representable as an 100 /// LLVM value, return it; otherwise, return nullptr. If a type is given, the 101 /// returned value must have the same type. This function is used by the 102 /// generic solver in attempting to resolve branch and switch conditions. 103 virtual Value *GetValueFromLatticeVal(LatticeVal LV, Type *Ty = nullptr) { 104 return nullptr; 105 } 106}; 107 108/// SparseSolver - This class is a general purpose solver for Sparse Conditional 109/// Propagation with a programmable lattice function. 110template <class LatticeKey, class LatticeVal, class KeyInfo> 111class SparseSolver { 112 113 /// LatticeFunc - This is the object that knows the lattice and how to 114 /// compute transfer functions. 115 AbstractLatticeFunction<LatticeKey, LatticeVal> *LatticeFunc; 116 117 /// ValueState - Holds the LatticeVals associated with LatticeKeys. 118 DenseMap<LatticeKey, LatticeVal> ValueState; 119 120 /// BBExecutable - Holds the basic blocks that are executable. 121 SmallPtrSet<BasicBlock *, 16> BBExecutable; 122 123 /// ValueWorkList - Holds values that should be processed. 124 SmallVector<Value *, 64> ValueWorkList; 125 126 /// BBWorkList - Holds basic blocks that should be processed. 127 SmallVector<BasicBlock *, 64> BBWorkList; 128 129 using Edge = std::pair<BasicBlock *, BasicBlock *>; 130 131 /// KnownFeasibleEdges - Entries in this set are edges which have already had 132 /// PHI nodes retriggered. 133 std::set<Edge> KnownFeasibleEdges; 134 135public: 136 explicit SparseSolver( 137 AbstractLatticeFunction<LatticeKey, LatticeVal> *Lattice) 138 : LatticeFunc(Lattice) {} 139 SparseSolver(const SparseSolver &) = delete; 140 SparseSolver &operator=(const SparseSolver &) = delete; 141 142 /// Solve - Solve for constants and executable blocks. 143 void Solve(); 144 145 void Print(raw_ostream &OS) const; 146 147 /// getExistingValueState - Return the LatticeVal object corresponding to the 148 /// given value from the ValueState map. If the value is not in the map, 149 /// UntrackedVal is returned, unlike the getValueState method. 150 LatticeVal getExistingValueState(LatticeKey Key) const { 151 auto I = ValueState.find(Key); 152 return I != ValueState.end() ? I->second : LatticeFunc->getUntrackedVal(); 153 } 154 155 /// getValueState - Return the LatticeVal object corresponding to the given 156 /// value from the ValueState map. If the value is not in the map, its state 157 /// is initialized. 158 LatticeVal getValueState(LatticeKey Key); 159 160 /// isEdgeFeasible - Return true if the control flow edge from the 'From' 161 /// basic block to the 'To' basic block is currently feasible. If 162 /// AggressiveUndef is true, then this treats values with unknown lattice 163 /// values as undefined. This is generally only useful when solving the 164 /// lattice, not when querying it. 165 bool isEdgeFeasible(BasicBlock *From, BasicBlock *To, 166 bool AggressiveUndef = false); 167 168 /// isBlockExecutable - Return true if there are any known feasible 169 /// edges into the basic block. This is generally only useful when 170 /// querying the lattice. 171 bool isBlockExecutable(BasicBlock *BB) const { 172 return BBExecutable.count(BB); 173 } 174 175 /// MarkBlockExecutable - This method can be used by clients to mark all of 176 /// the blocks that are known to be intrinsically live in the processed unit. 177 void MarkBlockExecutable(BasicBlock *BB); 178 179private: 180 /// UpdateState - When the state of some LatticeKey is potentially updated to 181 /// the given LatticeVal, this function notices and adds the LLVM value 182 /// corresponding the key to the work list, if needed. 183 void UpdateState(LatticeKey Key, LatticeVal LV); 184 185 /// markEdgeExecutable - Mark a basic block as executable, adding it to the BB 186 /// work list if it is not already executable. 187 void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest); 188 189 /// getFeasibleSuccessors - Return a vector of booleans to indicate which 190 /// successors are reachable from a given terminator instruction. 191 void getFeasibleSuccessors(Instruction &TI, SmallVectorImpl<bool> &Succs, 192 bool AggressiveUndef); 193 194 void visitInst(Instruction &I); 195 void visitPHINode(PHINode &I); 196 void visitTerminator(Instruction &TI); 197}; 198 199//===----------------------------------------------------------------------===// 200// AbstractLatticeFunction Implementation 201//===----------------------------------------------------------------------===// 202 203template <class LatticeKey, class LatticeVal> 204void AbstractLatticeFunction<LatticeKey, LatticeVal>::PrintLatticeVal( 205 LatticeVal V, raw_ostream &OS) { 206 if (V == UndefVal) 207 OS << "undefined"; 208 else if (V == OverdefinedVal) 209 OS << "overdefined"; 210 else if (V == UntrackedVal) 211 OS << "untracked"; 212 else 213 OS << "unknown lattice value"; 214} 215 216template <class LatticeKey, class LatticeVal> 217void AbstractLatticeFunction<LatticeKey, LatticeVal>::PrintLatticeKey( 218 LatticeKey Key, raw_ostream &OS) { 219 OS << "unknown lattice key"; 220} 221 222//===----------------------------------------------------------------------===// 223// SparseSolver Implementation 224//===----------------------------------------------------------------------===// 225 226template <class LatticeKey, class LatticeVal, class KeyInfo> 227LatticeVal 228SparseSolver<LatticeKey, LatticeVal, KeyInfo>::getValueState(LatticeKey Key) { 229 auto I = ValueState.find(Key); 230 if (I != ValueState.end()) 231 return I->second; // Common case, in the map 232 233 if (LatticeFunc->IsUntrackedValue(Key)) 234 return LatticeFunc->getUntrackedVal(); 235 LatticeVal LV = LatticeFunc->ComputeLatticeVal(Key); 236 237 // If this value is untracked, don't add it to the map. 238 if (LV == LatticeFunc->getUntrackedVal()) 239 return LV; 240 return ValueState[Key] = std::move(LV); 241} 242 243template <class LatticeKey, class LatticeVal, class KeyInfo> 244void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::UpdateState(LatticeKey Key, 245 LatticeVal LV) { 246 auto I = ValueState.find(Key); 247 if (I != ValueState.end() && I->second == LV) 248 return; // No change. 249 250 // Update the state of the given LatticeKey and add its corresponding LLVM 251 // value to the work list. 252 ValueState[Key] = std::move(LV); 253 if (Value *V = KeyInfo::getValueFromLatticeKey(Key)) 254 ValueWorkList.push_back(V); 255} 256 257template <class LatticeKey, class LatticeVal, class KeyInfo> 258void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::MarkBlockExecutable( 259 BasicBlock *BB) { 260 if (!BBExecutable.insert(BB).second) 261 return; 262 LLVM_DEBUG(dbgs() << "Marking Block Executable: " << BB->getName() << "\n"); 263 BBWorkList.push_back(BB); // Add the block to the work list! 264} 265 266template <class LatticeKey, class LatticeVal, class KeyInfo> 267void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::markEdgeExecutable( 268 BasicBlock *Source, BasicBlock *Dest) { 269 if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second) 270 return; // This edge is already known to be executable! 271 272 LLVM_DEBUG(dbgs() << "Marking Edge Executable: " << Source->getName() 273 << " -> " << Dest->getName() << "\n"); 274 275 if (BBExecutable.count(Dest)) { 276 // The destination is already executable, but we just made an edge 277 // feasible that wasn't before. Revisit the PHI nodes in the block 278 // because they have potentially new operands. 279 for (BasicBlock::iterator I = Dest->begin(); isa<PHINode>(I); ++I) 280 visitPHINode(*cast<PHINode>(I)); 281 } else { 282 MarkBlockExecutable(Dest); 283 } 284} 285 286template <class LatticeKey, class LatticeVal, class KeyInfo> 287void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::getFeasibleSuccessors( 288 Instruction &TI, SmallVectorImpl<bool> &Succs, bool AggressiveUndef) { 289 Succs.resize(TI.getNumSuccessors()); 290 if (TI.getNumSuccessors() == 0) 291 return; 292 293 if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) { 294 if (BI->isUnconditional()) { 295 Succs[0] = true; 296 return; 297 } 298 299 LatticeVal BCValue; 300 if (AggressiveUndef) 301 BCValue = 302 getValueState(KeyInfo::getLatticeKeyFromValue(BI->getCondition())); 303 else 304 BCValue = getExistingValueState( 305 KeyInfo::getLatticeKeyFromValue(BI->getCondition())); 306 307 if (BCValue == LatticeFunc->getOverdefinedVal() || 308 BCValue == LatticeFunc->getUntrackedVal()) { 309 // Overdefined condition variables can branch either way. 310 Succs[0] = Succs[1] = true; 311 return; 312 } 313 314 // If undefined, neither is feasible yet. 315 if (BCValue == LatticeFunc->getUndefVal()) 316 return; 317 318 Constant *C = 319 dyn_cast_or_null<Constant>(LatticeFunc->GetValueFromLatticeVal( 320 std::move(BCValue), BI->getCondition()->getType())); 321 if (!C || !isa<ConstantInt>(C)) { 322 // Non-constant values can go either way. 323 Succs[0] = Succs[1] = true; 324 return; 325 } 326 327 // Constant condition variables mean the branch can only go a single way 328 Succs[C->isNullValue()] = true; 329 return; 330 } 331 332 if (TI.isExceptionalTerminator() || 333 TI.isIndirectTerminator()) { 334 Succs.assign(Succs.size(), true); 335 return; 336 } 337 338 SwitchInst &SI = cast<SwitchInst>(TI); 339 LatticeVal SCValue; 340 if (AggressiveUndef) 341 SCValue = getValueState(KeyInfo::getLatticeKeyFromValue(SI.getCondition())); 342 else 343 SCValue = getExistingValueState( 344 KeyInfo::getLatticeKeyFromValue(SI.getCondition())); 345 346 if (SCValue == LatticeFunc->getOverdefinedVal() || 347 SCValue == LatticeFunc->getUntrackedVal()) { 348 // All destinations are executable! 349 Succs.assign(TI.getNumSuccessors(), true); 350 return; 351 } 352 353 // If undefined, neither is feasible yet. 354 if (SCValue == LatticeFunc->getUndefVal()) 355 return; 356 357 Constant *C = dyn_cast_or_null<Constant>(LatticeFunc->GetValueFromLatticeVal( 358 std::move(SCValue), SI.getCondition()->getType())); 359 if (!C || !isa<ConstantInt>(C)) { 360 // All destinations are executable! 361 Succs.assign(TI.getNumSuccessors(), true); 362 return; 363 } 364 SwitchInst::CaseHandle Case = *SI.findCaseValue(cast<ConstantInt>(C)); 365 Succs[Case.getSuccessorIndex()] = true; 366} 367 368template <class LatticeKey, class LatticeVal, class KeyInfo> 369bool SparseSolver<LatticeKey, LatticeVal, KeyInfo>::isEdgeFeasible( 370 BasicBlock *From, BasicBlock *To, bool AggressiveUndef) { 371 SmallVector<bool, 16> SuccFeasible; 372 Instruction *TI = From->getTerminator(); 373 getFeasibleSuccessors(*TI, SuccFeasible, AggressiveUndef); 374 375 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) 376 if (TI->getSuccessor(i) == To && SuccFeasible[i]) 377 return true; 378 379 return false; 380} 381 382template <class LatticeKey, class LatticeVal, class KeyInfo> 383void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::visitTerminator( 384 Instruction &TI) { 385 SmallVector<bool, 16> SuccFeasible; 386 getFeasibleSuccessors(TI, SuccFeasible, true); 387 388 BasicBlock *BB = TI.getParent(); 389 390 // Mark all feasible successors executable... 391 for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i) 392 if (SuccFeasible[i]) 393 markEdgeExecutable(BB, TI.getSuccessor(i)); 394} 395 396template <class LatticeKey, class LatticeVal, class KeyInfo> 397void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::visitPHINode(PHINode &PN) { 398 // The lattice function may store more information on a PHINode than could be 399 // computed from its incoming values. For example, SSI form stores its sigma 400 // functions as PHINodes with a single incoming value. 401 if (LatticeFunc->IsSpecialCasedPHI(&PN)) { 402 DenseMap<LatticeKey, LatticeVal> ChangedValues; 403 LatticeFunc->ComputeInstructionState(PN, ChangedValues, *this); 404 for (auto &ChangedValue : ChangedValues) 405 if (ChangedValue.second != LatticeFunc->getUntrackedVal()) 406 UpdateState(std::move(ChangedValue.first), 407 std::move(ChangedValue.second)); 408 return; 409 } 410 411 LatticeKey Key = KeyInfo::getLatticeKeyFromValue(&PN); 412 LatticeVal PNIV = getValueState(Key); 413 LatticeVal Overdefined = LatticeFunc->getOverdefinedVal(); 414 415 // If this value is already overdefined (common) just return. 416 if (PNIV == Overdefined || PNIV == LatticeFunc->getUntrackedVal()) 417 return; // Quick exit 418 419 // Super-extra-high-degree PHI nodes are unlikely to ever be interesting, 420 // and slow us down a lot. Just mark them overdefined. 421 if (PN.getNumIncomingValues() > 64) { 422 UpdateState(Key, Overdefined); 423 return; 424 } 425 426 // Look at all of the executable operands of the PHI node. If any of them 427 // are overdefined, the PHI becomes overdefined as well. Otherwise, ask the 428 // transfer function to give us the merge of the incoming values. 429 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) { 430 // If the edge is not yet known to be feasible, it doesn't impact the PHI. 431 if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent(), true)) 432 continue; 433 434 // Merge in this value. 435 LatticeVal OpVal = 436 getValueState(KeyInfo::getLatticeKeyFromValue(PN.getIncomingValue(i))); 437 if (OpVal != PNIV) 438 PNIV = LatticeFunc->MergeValues(PNIV, OpVal); 439 440 if (PNIV == Overdefined) 441 break; // Rest of input values don't matter. 442 } 443 444 // Update the PHI with the compute value, which is the merge of the inputs. 445 UpdateState(Key, PNIV); 446} 447 448template <class LatticeKey, class LatticeVal, class KeyInfo> 449void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::visitInst(Instruction &I) { 450 // PHIs are handled by the propagation logic, they are never passed into the 451 // transfer functions. 452 if (PHINode *PN = dyn_cast<PHINode>(&I)) 453 return visitPHINode(*PN); 454 455 // Otherwise, ask the transfer function what the result is. If this is 456 // something that we care about, remember it. 457 DenseMap<LatticeKey, LatticeVal> ChangedValues; 458 LatticeFunc->ComputeInstructionState(I, ChangedValues, *this); 459 for (auto &ChangedValue : ChangedValues) 460 if (ChangedValue.second != LatticeFunc->getUntrackedVal()) 461 UpdateState(ChangedValue.first, ChangedValue.second); 462 463 if (I.isTerminator()) 464 visitTerminator(I); 465} 466 467template <class LatticeKey, class LatticeVal, class KeyInfo> 468void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::Solve() { 469 // Process the work lists until they are empty! 470 while (!BBWorkList.empty() || !ValueWorkList.empty()) { 471 // Process the value work list. 472 while (!ValueWorkList.empty()) { 473 Value *V = ValueWorkList.pop_back_val(); 474 475 LLVM_DEBUG(dbgs() << "\nPopped off V-WL: " << *V << "\n"); 476 477 // "V" got into the work list because it made a transition. See if any 478 // users are both live and in need of updating. 479 for (User *U : V->users()) 480 if (Instruction *Inst = dyn_cast<Instruction>(U)) 481 if (BBExecutable.count(Inst->getParent())) // Inst is executable? 482 visitInst(*Inst); 483 } 484 485 // Process the basic block work list. 486 while (!BBWorkList.empty()) { 487 BasicBlock *BB = BBWorkList.pop_back_val(); 488 489 LLVM_DEBUG(dbgs() << "\nPopped off BBWL: " << *BB); 490 491 // Notify all instructions in this basic block that they are newly 492 // executable. 493 for (Instruction &I : *BB) 494 visitInst(I); 495 } 496 } 497} 498 499template <class LatticeKey, class LatticeVal, class KeyInfo> 500void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::Print( 501 raw_ostream &OS) const { 502 if (ValueState.empty()) 503 return; 504 505 LatticeKey Key; 506 LatticeVal LV; 507 508 OS << "ValueState:\n"; 509 for (auto &Entry : ValueState) { 510 std::tie(Key, LV) = Entry; 511 if (LV == LatticeFunc->getUntrackedVal()) 512 continue; 513 OS << "\t"; 514 LatticeFunc->PrintLatticeVal(LV, OS); 515 OS << ": "; 516 LatticeFunc->PrintLatticeKey(Key, OS); 517 OS << "\n"; 518 } 519} 520} // end namespace llvm 521 522#undef DEBUG_TYPE 523 524#endif // LLVM_ANALYSIS_SPARSEPROPAGATION_H 525