1 //===- LoopExtractor.cpp - Extract each loop into a new function ----------===// 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 // A pass wrapper around the ExtractLoop() scalar transformation to extract each 11 // top-level loop into its own new function. If the loop is the ONLY loop in a 12 // given function, it is not touched. This is a pass most useful for debugging 13 // via bugpoint. 14 // 15 //===----------------------------------------------------------------------===// 16 17 #include "llvm/Transforms/IPO.h" 18 #include "llvm/ADT/Statistic.h" 19 #include "llvm/Analysis/LoopPass.h" 20 #include "llvm/IR/Dominators.h" 21 #include "llvm/IR/Instructions.h" 22 #include "llvm/IR/Module.h" 23 #include "llvm/Pass.h" 24 #include "llvm/Support/CommandLine.h" 25 #include "llvm/Transforms/Scalar.h" 26 #include "llvm/Transforms/Utils/BasicBlockUtils.h" 27 #include "llvm/Transforms/Utils/CodeExtractor.h" 28 #include <fstream> 29 #include <set> 30 using namespace llvm; 31 32 #define DEBUG_TYPE "loop-extract" 33 34 STATISTIC(NumExtracted, "Number of loops extracted"); 35 36 namespace { 37 struct LoopExtractor : public LoopPass { 38 static char ID; // Pass identification, replacement for typeid 39 unsigned NumLoops; 40 41 explicit LoopExtractor(unsigned numLoops = ~0) 42 : LoopPass(ID), NumLoops(numLoops) { 43 initializeLoopExtractorPass(*PassRegistry::getPassRegistry()); 44 } 45 46 bool runOnLoop(Loop *L, LPPassManager &) override; 47 48 void getAnalysisUsage(AnalysisUsage &AU) const override { 49 AU.addRequiredID(BreakCriticalEdgesID); 50 AU.addRequiredID(LoopSimplifyID); 51 AU.addRequired<DominatorTreeWrapperPass>(); 52 AU.addRequired<LoopInfoWrapperPass>(); 53 } 54 }; 55 } 56 57 char LoopExtractor::ID = 0; 58 INITIALIZE_PASS_BEGIN(LoopExtractor, "loop-extract", 59 "Extract loops into new functions", false, false) 60 INITIALIZE_PASS_DEPENDENCY(BreakCriticalEdges) 61 INITIALIZE_PASS_DEPENDENCY(LoopSimplify) 62 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) 63 INITIALIZE_PASS_END(LoopExtractor, "loop-extract", 64 "Extract loops into new functions", false, false) 65 66 namespace { 67 /// SingleLoopExtractor - For bugpoint. 68 struct SingleLoopExtractor : public LoopExtractor { 69 static char ID; // Pass identification, replacement for typeid 70 SingleLoopExtractor() : LoopExtractor(1) {} 71 }; 72 } // End anonymous namespace 73 74 char SingleLoopExtractor::ID = 0; 75 INITIALIZE_PASS(SingleLoopExtractor, "loop-extract-single", 76 "Extract at most one loop into a new function", false, false) 77 78 // createLoopExtractorPass - This pass extracts all natural loops from the 79 // program into a function if it can. 80 // 81 Pass *llvm::createLoopExtractorPass() { return new LoopExtractor(); } 82 83 bool LoopExtractor::runOnLoop(Loop *L, LPPassManager &) { 84 if (skipLoop(L)) 85 return false; 86 87 // Only visit top-level loops. 88 if (L->getParentLoop()) 89 return false; 90 91 // If LoopSimplify form is not available, stay out of trouble. 92 if (!L->isLoopSimplifyForm()) 93 return false; 94 95 DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree(); 96 LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); 97 bool Changed = false; 98 99 // If there is more than one top-level loop in this function, extract all of 100 // the loops. Otherwise there is exactly one top-level loop; in this case if 101 // this function is more than a minimal wrapper around the loop, extract 102 // the loop. 103 bool ShouldExtractLoop = false; 104 105 // Extract the loop if the entry block doesn't branch to the loop header. 106 TerminatorInst *EntryTI = 107 L->getHeader()->getParent()->getEntryBlock().getTerminator(); 108 if (!isa<BranchInst>(EntryTI) || 109 !cast<BranchInst>(EntryTI)->isUnconditional() || 110 EntryTI->getSuccessor(0) != L->getHeader()) { 111 ShouldExtractLoop = true; 112 } else { 113 // Check to see if any exits from the loop are more than just return 114 // blocks. 115 SmallVector<BasicBlock*, 8> ExitBlocks; 116 L->getExitBlocks(ExitBlocks); 117 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) 118 if (!isa<ReturnInst>(ExitBlocks[i]->getTerminator())) { 119 ShouldExtractLoop = true; 120 break; 121 } 122 } 123 124 if (ShouldExtractLoop) { 125 // We must omit EH pads. EH pads must accompany the invoke 126 // instruction. But this would result in a loop in the extracted 127 // function. An infinite cycle occurs when it tries to extract that loop as 128 // well. 129 SmallVector<BasicBlock*, 8> ExitBlocks; 130 L->getExitBlocks(ExitBlocks); 131 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) 132 if (ExitBlocks[i]->isEHPad()) { 133 ShouldExtractLoop = false; 134 break; 135 } 136 } 137 138 if (ShouldExtractLoop) { 139 if (NumLoops == 0) return Changed; 140 --NumLoops; 141 CodeExtractor Extractor(DT, *L); 142 if (Extractor.extractCodeRegion() != nullptr) { 143 Changed = true; 144 // After extraction, the loop is replaced by a function call, so 145 // we shouldn't try to run any more loop passes on it. 146 LI.markAsRemoved(L); 147 } 148 ++NumExtracted; 149 } 150 151 return Changed; 152 } 153 154 // createSingleLoopExtractorPass - This pass extracts one natural loop from the 155 // program into a function if it can. This is used by bugpoint. 156 // 157 Pass *llvm::createSingleLoopExtractorPass() { 158 return new SingleLoopExtractor(); 159 } 160 161 162 // BlockFile - A file which contains a list of blocks that should not be 163 // extracted. 164 static cl::opt<std::string> 165 BlockFile("extract-blocks-file", cl::value_desc("filename"), 166 cl::desc("A file containing list of basic blocks to not extract"), 167 cl::Hidden); 168 169 namespace { 170 /// BlockExtractorPass - This pass is used by bugpoint to extract all blocks 171 /// from the module into their own functions except for those specified by the 172 /// BlocksToNotExtract list. 173 class BlockExtractorPass : public ModulePass { 174 void LoadFile(const char *Filename); 175 void SplitLandingPadPreds(Function *F); 176 177 std::vector<BasicBlock*> BlocksToNotExtract; 178 std::vector<std::pair<std::string, std::string> > BlocksToNotExtractByName; 179 public: 180 static char ID; // Pass identification, replacement for typeid 181 BlockExtractorPass() : ModulePass(ID) { 182 if (!BlockFile.empty()) 183 LoadFile(BlockFile.c_str()); 184 } 185 186 bool runOnModule(Module &M) override; 187 }; 188 } 189 190 char BlockExtractorPass::ID = 0; 191 INITIALIZE_PASS(BlockExtractorPass, "extract-blocks", 192 "Extract Basic Blocks From Module (for bugpoint use)", 193 false, false) 194 195 // createBlockExtractorPass - This pass extracts all blocks (except those 196 // specified in the argument list) from the functions in the module. 197 // 198 ModulePass *llvm::createBlockExtractorPass() { 199 return new BlockExtractorPass(); 200 } 201 202 void BlockExtractorPass::LoadFile(const char *Filename) { 203 // Load the BlockFile... 204 std::ifstream In(Filename); 205 if (!In.good()) { 206 errs() << "WARNING: BlockExtractor couldn't load file '" << Filename 207 << "'!\n"; 208 return; 209 } 210 while (In) { 211 std::string FunctionName, BlockName; 212 In >> FunctionName; 213 In >> BlockName; 214 if (!BlockName.empty()) 215 BlocksToNotExtractByName.push_back( 216 std::make_pair(FunctionName, BlockName)); 217 } 218 } 219 220 /// SplitLandingPadPreds - The landing pad needs to be extracted with the invoke 221 /// instruction. The critical edge breaker will refuse to break critical edges 222 /// to a landing pad. So do them here. After this method runs, all landing pads 223 /// should have only one predecessor. 224 void BlockExtractorPass::SplitLandingPadPreds(Function *F) { 225 for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) { 226 InvokeInst *II = dyn_cast<InvokeInst>(I); 227 if (!II) continue; 228 BasicBlock *Parent = II->getParent(); 229 BasicBlock *LPad = II->getUnwindDest(); 230 231 // Look through the landing pad's predecessors. If one of them ends in an 232 // 'invoke', then we want to split the landing pad. 233 bool Split = false; 234 for (pred_iterator 235 PI = pred_begin(LPad), PE = pred_end(LPad); PI != PE; ++PI) { 236 BasicBlock *BB = *PI; 237 if (BB->isLandingPad() && BB != Parent && 238 isa<InvokeInst>(Parent->getTerminator())) { 239 Split = true; 240 break; 241 } 242 } 243 244 if (!Split) continue; 245 246 SmallVector<BasicBlock*, 2> NewBBs; 247 SplitLandingPadPredecessors(LPad, Parent, ".1", ".2", NewBBs); 248 } 249 } 250 251 bool BlockExtractorPass::runOnModule(Module &M) { 252 if (skipModule(M)) 253 return false; 254 255 std::set<BasicBlock*> TranslatedBlocksToNotExtract; 256 for (unsigned i = 0, e = BlocksToNotExtract.size(); i != e; ++i) { 257 BasicBlock *BB = BlocksToNotExtract[i]; 258 Function *F = BB->getParent(); 259 260 // Map the corresponding function in this module. 261 Function *MF = M.getFunction(F->getName()); 262 assert(MF->getFunctionType() == F->getFunctionType() && "Wrong function?"); 263 264 // Figure out which index the basic block is in its function. 265 Function::iterator BBI = MF->begin(); 266 std::advance(BBI, std::distance(F->begin(), Function::iterator(BB))); 267 TranslatedBlocksToNotExtract.insert(&*BBI); 268 } 269 270 while (!BlocksToNotExtractByName.empty()) { 271 // There's no way to find BBs by name without looking at every BB inside 272 // every Function. Fortunately, this is always empty except when used by 273 // bugpoint in which case correctness is more important than performance. 274 275 std::string &FuncName = BlocksToNotExtractByName.back().first; 276 std::string &BlockName = BlocksToNotExtractByName.back().second; 277 278 for (Function &F : M) { 279 if (F.getName() != FuncName) continue; 280 281 for (BasicBlock &BB : F) { 282 if (BB.getName() != BlockName) continue; 283 284 TranslatedBlocksToNotExtract.insert(&BB); 285 } 286 } 287 288 BlocksToNotExtractByName.pop_back(); 289 } 290 291 // Now that we know which blocks to not extract, figure out which ones we WANT 292 // to extract. 293 std::vector<BasicBlock*> BlocksToExtract; 294 for (Function &F : M) { 295 SplitLandingPadPreds(&F); 296 for (BasicBlock &BB : F) 297 if (!TranslatedBlocksToNotExtract.count(&BB)) 298 BlocksToExtract.push_back(&BB); 299 } 300 301 for (BasicBlock *BlockToExtract : BlocksToExtract) { 302 SmallVector<BasicBlock*, 2> BlocksToExtractVec; 303 BlocksToExtractVec.push_back(BlockToExtract); 304 if (const InvokeInst *II = 305 dyn_cast<InvokeInst>(BlockToExtract->getTerminator())) 306 BlocksToExtractVec.push_back(II->getUnwindDest()); 307 CodeExtractor(BlocksToExtractVec).extractCodeRegion(); 308 } 309 310 return !BlocksToExtract.empty(); 311 } 312