SparsePropagation.cpp revision afcde473c5baf292038ec494917f18c77a043340
1//===- SparsePropagation.cpp - Sparse Conditional Property Propagation ----===// 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 file implements an abstract sparse conditional propagation algorithm, 11// modeled after SCCP, but with a customizable lattice function. 12// 13//===----------------------------------------------------------------------===// 14 15#define DEBUG_TYPE "sparseprop" 16#include "llvm/Analysis/SparsePropagation.h" 17#include "llvm/Constants.h" 18#include "llvm/Function.h" 19#include "llvm/Instructions.h" 20#include "llvm/Support/Debug.h" 21using namespace llvm; 22 23//===----------------------------------------------------------------------===// 24// AbstractLatticeFunction Implementation 25//===----------------------------------------------------------------------===// 26 27AbstractLatticeFunction::~AbstractLatticeFunction() {} 28 29/// PrintValue - Render the specified lattice value to the specified stream. 30void AbstractLatticeFunction::PrintValue(LatticeVal V, std::ostream &OS) { 31 if (V == UndefVal) 32 OS << "undefined"; 33 else if (V == OverdefinedVal) 34 OS << "overdefined"; 35 else if (V == UntrackedVal) 36 OS << "untracked"; 37 else 38 OS << "unknown lattice value"; 39} 40 41//===----------------------------------------------------------------------===// 42// SparseSolver Implementation 43//===----------------------------------------------------------------------===// 44 45/// getOrInitValueState - Return the LatticeVal object that corresponds to the 46/// value, initializing the value's state if it hasn't been entered into the 47/// map yet. This function is necessary because not all values should start 48/// out in the underdefined state... Arguments should be overdefined, and 49/// constants should be marked as constants. 50/// 51SparseSolver::LatticeVal SparseSolver::getOrInitValueState(Value *V) { 52 DenseMap<Value*, LatticeVal>::iterator I = ValueState.find(V); 53 if (I != ValueState.end()) return I->second; // Common case, in the map 54 55 LatticeVal LV; 56 if (LatticeFunc->IsUntrackedValue(V)) 57 return LatticeFunc->getUntrackedVal(); 58 else if (Constant *C = dyn_cast<Constant>(V)) 59 LV = LatticeFunc->ComputeConstant(C); 60 else if (Argument *A = dyn_cast<Argument>(V)) 61 LV = LatticeFunc->ComputeArgument(A); 62 else if (!isa<Instruction>(V)) 63 // All other non-instructions are overdefined. 64 LV = LatticeFunc->getOverdefinedVal(); 65 else 66 // All instructions are underdefined by default. 67 LV = LatticeFunc->getUndefVal(); 68 69 // If this value is untracked, don't add it to the map. 70 if (LV == LatticeFunc->getUntrackedVal()) 71 return LV; 72 return ValueState[V] = LV; 73} 74 75/// UpdateState - When the state for some instruction is potentially updated, 76/// this function notices and adds I to the worklist if needed. 77void SparseSolver::UpdateState(Instruction &Inst, LatticeVal V) { 78 DenseMap<Value*, LatticeVal>::iterator I = ValueState.find(&Inst); 79 if (I != ValueState.end() && I->second == V) 80 return; // No change. 81 82 // An update. Visit uses of I. 83 ValueState[&Inst] = V; 84 InstWorkList.push_back(&Inst); 85} 86 87/// MarkBlockExecutable - This method can be used by clients to mark all of 88/// the blocks that are known to be intrinsically live in the processed unit. 89void SparseSolver::MarkBlockExecutable(BasicBlock *BB) { 90 DOUT << "Marking Block Executable: " << BB->getNameStart() << "\n"; 91 BBExecutable.insert(BB); // Basic block is executable! 92 BBWorkList.push_back(BB); // Add the block to the work list! 93} 94 95/// markEdgeExecutable - Mark a basic block as executable, adding it to the BB 96/// work list if it is not already executable... 97void SparseSolver::markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) { 98 if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second) 99 return; // This edge is already known to be executable! 100 101 DOUT << "Marking Edge Executable: " << Source->getNameStart() 102 << " -> " << Dest->getNameStart() << "\n"; 103 104 if (BBExecutable.count(Dest)) { 105 // The destination is already executable, but we just made an edge 106 // feasible that wasn't before. Revisit the PHI nodes in the block 107 // because they have potentially new operands. 108 for (BasicBlock::iterator I = Dest->begin(); isa<PHINode>(I); ++I) 109 visitPHINode(*cast<PHINode>(I)); 110 111 } else { 112 MarkBlockExecutable(Dest); 113 } 114} 115 116 117/// getFeasibleSuccessors - Return a vector of booleans to indicate which 118/// successors are reachable from a given terminator instruction. 119void SparseSolver::getFeasibleSuccessors(TerminatorInst &TI, 120 SmallVectorImpl<bool> &Succs, 121 bool AggressiveUndef) { 122 Succs.resize(TI.getNumSuccessors()); 123 if (TI.getNumSuccessors() == 0) return; 124 125 if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) { 126 if (BI->isUnconditional()) { 127 Succs[0] = true; 128 return; 129 } 130 131 LatticeVal BCValue; 132 if (AggressiveUndef) 133 BCValue = getOrInitValueState(BI->getCondition()); 134 else 135 BCValue = getLatticeState(BI->getCondition()); 136 137 if (BCValue == LatticeFunc->getOverdefinedVal() || 138 BCValue == LatticeFunc->getUntrackedVal()) { 139 // Overdefined condition variables can branch either way. 140 Succs[0] = Succs[1] = true; 141 return; 142 } 143 144 // If undefined, neither is feasible yet. 145 if (BCValue == LatticeFunc->getUndefVal()) 146 return; 147 148 Constant *C = LatticeFunc->GetConstant(BCValue, BI->getCondition(), *this); 149 if (C == 0 || !isa<ConstantInt>(C)) { 150 // Non-constant values can go either way. 151 Succs[0] = Succs[1] = true; 152 return; 153 } 154 155 // Constant condition variables mean the branch can only go a single way 156 Succs[C == ConstantInt::getFalse()] = true; 157 return; 158 } 159 160 if (isa<InvokeInst>(TI)) { 161 // Invoke instructions successors are always executable. 162 // TODO: Could ask the lattice function if the value can throw. 163 Succs[0] = Succs[1] = true; 164 return; 165 } 166 167 SwitchInst &SI = cast<SwitchInst>(TI); 168 LatticeVal SCValue; 169 if (AggressiveUndef) 170 SCValue = getOrInitValueState(SI.getCondition()); 171 else 172 SCValue = getLatticeState(SI.getCondition()); 173 174 if (SCValue == LatticeFunc->getOverdefinedVal() || 175 SCValue == LatticeFunc->getUntrackedVal()) { 176 // All destinations are executable! 177 Succs.assign(TI.getNumSuccessors(), true); 178 return; 179 } 180 181 // If undefined, neither is feasible yet. 182 if (SCValue == LatticeFunc->getUndefVal()) 183 return; 184 185 Constant *C = LatticeFunc->GetConstant(SCValue, SI.getCondition(), *this); 186 if (C == 0 || !isa<ConstantInt>(C)) { 187 // All destinations are executable! 188 Succs.assign(TI.getNumSuccessors(), true); 189 return; 190 } 191 192 Succs[SI.findCaseValue(cast<ConstantInt>(C))] = true; 193} 194 195 196/// isEdgeFeasible - Return true if the control flow edge from the 'From' 197/// basic block to the 'To' basic block is currently feasible... 198bool SparseSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To, 199 bool AggressiveUndef) { 200 SmallVector<bool, 16> SuccFeasible; 201 TerminatorInst *TI = From->getTerminator(); 202 getFeasibleSuccessors(*TI, SuccFeasible, AggressiveUndef); 203 204 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) 205 if (TI->getSuccessor(i) == To && SuccFeasible[i]) 206 return true; 207 208 return false; 209} 210 211void SparseSolver::visitTerminatorInst(TerminatorInst &TI) { 212 SmallVector<bool, 16> SuccFeasible; 213 getFeasibleSuccessors(TI, SuccFeasible, true); 214 215 BasicBlock *BB = TI.getParent(); 216 217 // Mark all feasible successors executable... 218 for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i) 219 if (SuccFeasible[i]) 220 markEdgeExecutable(BB, TI.getSuccessor(i)); 221} 222 223void SparseSolver::visitPHINode(PHINode &PN) { 224 LatticeVal PNIV = getOrInitValueState(&PN); 225 LatticeVal Overdefined = LatticeFunc->getOverdefinedVal(); 226 227 // If this value is already overdefined (common) just return. 228 if (PNIV == Overdefined || PNIV == LatticeFunc->getUntrackedVal()) 229 return; // Quick exit 230 231 // Super-extra-high-degree PHI nodes are unlikely to ever be interesting, 232 // and slow us down a lot. Just mark them overdefined. 233 if (PN.getNumIncomingValues() > 64) { 234 UpdateState(PN, Overdefined); 235 return; 236 } 237 238 // Look at all of the executable operands of the PHI node. If any of them 239 // are overdefined, the PHI becomes overdefined as well. Otherwise, ask the 240 // transfer function to give us the merge of the incoming values. 241 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) { 242 // If the edge is not yet known to be feasible, it doesn't impact the PHI. 243 if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent(), true)) 244 continue; 245 246 // Merge in this value. 247 LatticeVal OpVal = getOrInitValueState(PN.getIncomingValue(i)); 248 if (OpVal != PNIV) 249 PNIV = LatticeFunc->MergeValues(PNIV, OpVal); 250 251 if (PNIV == Overdefined) 252 break; // Rest of input values don't matter. 253 } 254 255 // Update the PHI with the compute value, which is the merge of the inputs. 256 UpdateState(PN, PNIV); 257} 258 259 260void SparseSolver::visitInst(Instruction &I) { 261 // PHIs are handled by the propagation logic, they are never passed into the 262 // transfer functions. 263 if (PHINode *PN = dyn_cast<PHINode>(&I)) 264 return visitPHINode(*PN); 265 266 // Otherwise, ask the transfer function what the result is. If this is 267 // something that we care about, remember it. 268 LatticeVal IV = LatticeFunc->ComputeInstructionState(I, *this); 269 if (IV != LatticeFunc->getUntrackedVal()) 270 UpdateState(I, IV); 271 272 if (TerminatorInst *TI = dyn_cast<TerminatorInst>(&I)) 273 visitTerminatorInst(*TI); 274} 275 276void SparseSolver::Solve(Function &F) { 277 MarkBlockExecutable(&F.getEntryBlock()); 278 279 // Process the work lists until they are empty! 280 while (!BBWorkList.empty() || !InstWorkList.empty()) { 281 // Process the instruction work list. 282 while (!InstWorkList.empty()) { 283 Instruction *I = InstWorkList.back(); 284 InstWorkList.pop_back(); 285 286 DOUT << "\nPopped off I-WL: " << *I; 287 288 // "I" got into the work list because it made a transition. See if any 289 // users are both live and in need of updating. 290 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); 291 UI != E; ++UI) { 292 Instruction *U = cast<Instruction>(*UI); 293 if (BBExecutable.count(U->getParent())) // Inst is executable? 294 visitInst(*U); 295 } 296 } 297 298 // Process the basic block work list. 299 while (!BBWorkList.empty()) { 300 BasicBlock *BB = BBWorkList.back(); 301 BBWorkList.pop_back(); 302 303 DOUT << "\nPopped off BBWL: " << *BB; 304 305 // Notify all instructions in this basic block that they are newly 306 // executable. 307 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 308 visitInst(*I); 309 } 310 } 311} 312 313void SparseSolver::Print(Function &F, std::ostream &OS) { 314 OS << "\nFUNCTION: " << F.getNameStr() << "\n"; 315 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { 316 if (!BBExecutable.count(BB)) 317 OS << "INFEASIBLE: "; 318 OS << "\t"; 319 if (BB->hasName()) 320 OS << BB->getNameStr() << ":\n"; 321 else 322 OS << "; anon bb\n"; 323 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { 324 LatticeFunc->PrintValue(getLatticeState(I), OS); 325 OS << *I; 326 } 327 328 OS << "\n"; 329 } 330} 331 332