lib/Transforms/IPO/LoopExtractor.cpp

   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 #define DEBUG_TYPE "loop-extract"
  18 #include "llvm/Transforms/IPO.h"
  19 #include "llvm/Instructions.h"
  20 #include "llvm/Module.h"
  21 #include "llvm/Pass.h"
  22 #include "llvm/Analysis/Dominators.h"
  23 #include "llvm/Analysis/LoopPass.h"
  24 #include "llvm/Support/CommandLine.h"
  25 #include "llvm/Transforms/Scalar.h"
  26 #include "llvm/Transforms/Utils/FunctionUtils.h"
  27 #include "llvm/ADT/Statistic.h"
  28 #include <fstream>
  29 #include <set>
  30 using namespace llvm;
  31
  32 STATISTIC(NumExtracted, "Number of loops extracted");
  33
  34 namespace {
  35   struct LoopExtractor : public LoopPass {
  36     static char ID; // Pass identification, replacement for typeid
  37     unsigned NumLoops;
  38
  39     explicit LoopExtractor(unsigned numLoops = ~0)
  40       : LoopPass(ID), NumLoops(numLoops) {
  41         initializeLoopExtractorPass(*PassRegistry::getPassRegistry());
  42       }
  43
  44     virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
  45
  46     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  47       AU.addRequiredID(BreakCriticalEdgesID);
  48       AU.addRequiredID(LoopSimplifyID);
  49       AU.addRequired<DominatorTree>();
  50     }
  51   };
  52 }
  53
  54 char LoopExtractor::ID = 0;
  55 INITIALIZE_PASS_BEGIN(LoopExtractor, "loop-extract",
  56                 "Extract loops into new functions", false, false)
  57 INITIALIZE_PASS_DEPENDENCY(BreakCriticalEdges)
  58 INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
  59 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
  60 INITIALIZE_PASS_END(LoopExtractor, "loop-extract",
  61                 "Extract loops into new functions", false, false)
  62
  63 namespace {
  64   /// SingleLoopExtractor - For bugpoint.
  65   struct SingleLoopExtractor : public LoopExtractor {
  66     static char ID; // Pass identification, replacement for typeid
  67     SingleLoopExtractor() : LoopExtractor(1) {}
  68   };
  69 } // End anonymous namespace
  70
  71 char SingleLoopExtractor::ID = 0;
  72 INITIALIZE_PASS(SingleLoopExtractor, "loop-extract-single",
  73                 "Extract at most one loop into a new function", false, false)
  74
  75 // createLoopExtractorPass - This pass extracts all natural loops from the
  76 // program into a function if it can.
  77 //
  78 Pass *llvm::createLoopExtractorPass() { return new LoopExtractor(); }
  79
  80 bool LoopExtractor::runOnLoop(Loop *L, LPPassManager &LPM) {
  81   // Only visit top-level loops.
  82   if (L->getParentLoop())
  83     return false;
  84
  85   // If LoopSimplify form is not available, stay out of trouble.
  86   if (!L->isLoopSimplifyForm())
  87     return false;
  88
  89   DominatorTree &DT = getAnalysis<DominatorTree>();
  90   bool Changed = false;
  91
  92   // If there is more than one top-level loop in this function, extract all of
  93   // the loops. Otherwise there is exactly one top-level loop; in this case if
  94   // this function is more than a minimal wrapper around the loop, extract
  95   // the loop.
  96   bool ShouldExtractLoop = false;
  97
  98   // Extract the loop if the entry block doesn't branch to the loop header.
  99   TerminatorInst *EntryTI =
 100     L->getHeader()->getParent()->getEntryBlock().getTerminator();
 101   if (!isa<BranchInst>(EntryTI) ||
 102       !cast<BranchInst>(EntryTI)->isUnconditional() ||
 103       EntryTI->getSuccessor(0) != L->getHeader())
 104     ShouldExtractLoop = true;
 105   else {
 106     // Check to see if any exits from the loop are more than just return
 107     // blocks.
 108     SmallVector<BasicBlock*, 8> ExitBlocks;
 109     L->getExitBlocks(ExitBlocks);
 110     for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
 111       if (!isa<ReturnInst>(ExitBlocks[i]->getTerminator())) {
 112         ShouldExtractLoop = true;
 113         break;
 114       }
 115   }
 116   if (ShouldExtractLoop) {
 117     if (NumLoops == 0) return Changed;
 118     --NumLoops;
 119     if (ExtractLoop(DT, L) != 0) {
 120       Changed = true;
 121       // After extraction, the loop is replaced by a function call, so
 122       // we shouldn't try to run any more loop passes on it.
 123       LPM.deleteLoopFromQueue(L);
 124     }
 125     ++NumExtracted;
 126   }
 127
 128   return Changed;
 129 }
 130
 131 // createSingleLoopExtractorPass - This pass extracts one natural loop from the
 132 // program into a function if it can.  This is used by bugpoint.
 133 //
 134 Pass *llvm::createSingleLoopExtractorPass() {
 135   return new SingleLoopExtractor();
 136 }
 137
 138
 139 // BlockFile - A file which contains a list of blocks that should not be
 140 // extracted.
 141 static cl::opt<std::string>
 142 BlockFile("extract-blocks-file", cl::value_desc("filename"),
 143           cl::desc("A file containing list of basic blocks to not extract"),
 144           cl::Hidden);
 145
 146 namespace {
 147   /// BlockExtractorPass - This pass is used by bugpoint to extract all blocks
 148   /// from the module into their own functions except for those specified by the
 149   /// BlocksToNotExtract list.
 150   class BlockExtractorPass : public ModulePass {
 151     void LoadFile(const char *Filename);
 152
 153     std::vector<BasicBlock*> BlocksToNotExtract;
 154     std::vector<std::pair<std::string, std::string> > BlocksToNotExtractByName;
 155   public:
 156     static char ID; // Pass identification, replacement for typeid
 157     BlockExtractorPass() : ModulePass(ID) {
 158       if (!BlockFile.empty())
 159         LoadFile(BlockFile.c_str());
 160     }
 161
 162     bool runOnModule(Module &M);
 163   };
 164 }
 165
 166 char BlockExtractorPass::ID = 0;
 167 INITIALIZE_PASS(BlockExtractorPass, "extract-blocks",
 168                 "Extract Basic Blocks From Module (for bugpoint use)",
 169                 false, false)
 170
 171 // createBlockExtractorPass - This pass extracts all blocks (except those
 172 // specified in the argument list) from the functions in the module.
 173 //
 174 ModulePass *llvm::createBlockExtractorPass()
 175 {
 176   return new BlockExtractorPass();
 177 }
 178
 179 void BlockExtractorPass::LoadFile(const char *Filename) {
 180   // Load the BlockFile...
 181   std::ifstream In(Filename);
 182   if (!In.good()) {
 183     errs() << "WARNING: BlockExtractor couldn't load file '" << Filename
 184            << "'!\n";
 185     return;
 186   }
 187   while (In) {
 188     std::string FunctionName, BlockName;
 189     In >> FunctionName;
 190     In >> BlockName;
 191     if (!BlockName.empty())
 192       BlocksToNotExtractByName.push_back(
 193           std::make_pair(FunctionName, BlockName));
 194   }
 195 }
 196
 197 bool BlockExtractorPass::runOnModule(Module &M) {
 198   std::set<BasicBlock*> TranslatedBlocksToNotExtract;
 199   for (unsigned i = 0, e = BlocksToNotExtract.size(); i != e; ++i) {
 200     BasicBlock *BB = BlocksToNotExtract[i];
 201     Function *F = BB->getParent();
 202
 203     // Map the corresponding function in this module.
 204     Function *MF = M.getFunction(F->getName());
 205     assert(MF->getFunctionType() == F->getFunctionType() && "Wrong function?");
 206
 207     // Figure out which index the basic block is in its function.
 208     Function::iterator BBI = MF->begin();
 209     std::advance(BBI, std::distance(F->begin(), Function::iterator(BB)));
 210     TranslatedBlocksToNotExtract.insert(BBI);
 211   }
 212
 213   while (!BlocksToNotExtractByName.empty()) {
 214     // There's no way to find BBs by name without looking at every BB inside
 215     // every Function. Fortunately, this is always empty except when used by
 216     // bugpoint in which case correctness is more important than performance.
 217
 218     std::string &FuncName  = BlocksToNotExtractByName.back().first;
 219     std::string &BlockName = BlocksToNotExtractByName.back().second;
 220
 221     for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI) {
 222       Function &F = *FI;
 223       if (F.getName() != FuncName) continue;
 224
 225       for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
 226         BasicBlock &BB = *BI;
 227         if (BB.getName() != BlockName) continue;
 228
 229         TranslatedBlocksToNotExtract.insert(BI);
 230       }
 231     }
 232
 233     BlocksToNotExtractByName.pop_back();
 234   }
 235
 236   // Now that we know which blocks to not extract, figure out which ones we WANT
 237   // to extract.
 238   std::vector<BasicBlock*> BlocksToExtract;
 239   for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
 240     for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
 241       if (!TranslatedBlocksToNotExtract.count(BB))
 242         BlocksToExtract.push_back(BB);
 243
 244   for (unsigned i = 0, e = BlocksToExtract.size(); i != e; ++i)
 245     ExtractBasicBlock(BlocksToExtract[i]);
 246
 247   return !BlocksToExtract.empty();
 248 }