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