LoopExtractor.cpp revision 081ce940e7351e90fff829320b7dc6738a6b3815 
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/LoopInfo.h"
24#include "llvm/Support/CommandLine.h"
25#include "llvm/Support/Compiler.h"
26#include "llvm/Transforms/Scalar.h"
27#include "llvm/Transforms/Utils/FunctionUtils.h"
28#include "llvm/ADT/Statistic.h"
29#include <fstream>
30#include <set>
31using namespace llvm;
32
33STATISTIC(NumExtracted, "Number of loops extracted");
34
35namespace {
36  // FIXME: This is not a function pass, but the PassManager doesn't allow
37  // Module passes to require FunctionPasses, so we can't get loop info if we're
38  // not a function pass.
39  struct VISIBILITY_HIDDEN LoopExtractor : public FunctionPass {
40    static char ID; // Pass identification, replacement for typeid
41    unsigned NumLoops;
42
43    explicit LoopExtractor(unsigned numLoops = ~0)
44      : FunctionPass((intptr_t)&ID), NumLoops(numLoops) {}
45
46    virtual bool runOnFunction(Function &F);
47
48    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
49      AU.addRequiredID(BreakCriticalEdgesID);
50      AU.addRequiredID(LoopSimplifyID);
51      AU.addRequired<DominatorTree>();
52      AU.addRequired<LoopInfo>();
53    }
54  };
55
56  char LoopExtractor::ID = 0;
57  RegisterPass<LoopExtractor>
58  X("loop-extract", "Extract loops into new functions");
59
60  /// SingleLoopExtractor - For bugpoint.
61  struct SingleLoopExtractor : public LoopExtractor {
62    static char ID; // Pass identification, replacement for typeid
63    SingleLoopExtractor() : LoopExtractor(1) {}
64  };
65
66  char SingleLoopExtractor::ID = 0;
67  RegisterPass<SingleLoopExtractor>
68  Y("loop-extract-single", "Extract at most one loop into a new function");
69} // End anonymous namespace
70
71// createLoopExtractorPass - This pass extracts all natural loops from the
72// program into a function if it can.
73//
74FunctionPass *llvm::createLoopExtractorPass() { return new LoopExtractor(); }
75
76bool LoopExtractor::runOnFunction(Function &F) {
77  LoopInfo &LI = getAnalysis<LoopInfo>();
78
79  // If this function has no loops, there is nothing to do.
80  if (LI.begin() == LI.end())
81    return false;
82
83  DominatorTree &DT = getAnalysis<DominatorTree>();
84
85  // If there is more than one top-level loop in this function, extract all of
86  // the loops.
87  bool Changed = false;
88  if (LI.end()-LI.begin() > 1) {
89    for (LoopInfo::iterator i = LI.begin(), e = LI.end(); i != e; ++i) {
90      if (NumLoops == 0) return Changed;
91      --NumLoops;
92      Changed |= ExtractLoop(DT, *i) != 0;
93      ++NumExtracted;
94    }
95  } else {
96    // Otherwise there is exactly one top-level loop.  If this function is more
97    // than a minimal wrapper around the loop, extract the loop.
98    Loop *TLL = *LI.begin();
99    bool ShouldExtractLoop = false;
100
101    // Extract the loop if the entry block doesn't branch to the loop header.
102    TerminatorInst *EntryTI = F.getEntryBlock().getTerminator();
103    if (!isa<BranchInst>(EntryTI) ||
104        !cast<BranchInst>(EntryTI)->isUnconditional() ||
105        EntryTI->getSuccessor(0) != TLL->getHeader())
106      ShouldExtractLoop = true;
107    else {
108      // Check to see if any exits from the loop are more than just return
109      // blocks.
110      SmallVector<BasicBlock*, 8> ExitBlocks;
111      TLL->getExitBlocks(ExitBlocks);
112      for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
113        if (!isa<ReturnInst>(ExitBlocks[i]->getTerminator())) {
114          ShouldExtractLoop = true;
115          break;
116        }
117    }
118
119    if (ShouldExtractLoop) {
120      if (NumLoops == 0) return Changed;
121      --NumLoops;
122      Changed |= ExtractLoop(DT, TLL) != 0;
123      ++NumExtracted;
124    } else {
125      // Okay, this function is a minimal container around the specified loop.
126      // If we extract the loop, we will continue to just keep extracting it
127      // infinitely... so don't extract it.  However, if the loop contains any
128      // subloops, extract them.
129      for (Loop::iterator i = TLL->begin(), e = TLL->end(); i != e; ++i) {
130        if (NumLoops == 0) return Changed;
131        --NumLoops;
132        Changed |= ExtractLoop(DT, *i) != 0;
133        ++NumExtracted;
134      }
135    }
136  }
137
138  return Changed;
139}
140
141// createSingleLoopExtractorPass - This pass extracts one natural loop from the
142// program into a function if it can.  This is used by bugpoint.
143//
144FunctionPass *llvm::createSingleLoopExtractorPass() {
145  return new SingleLoopExtractor();
146}
147
148
149namespace {
150  // BlockFile - A file which contains a list of blocks that should not be
151  // extracted.
152  cl::opt<std::string>
153  BlockFile("extract-blocks-file", cl::value_desc("filename"),
154            cl::desc("A file containing list of basic blocks to not extract"),
155            cl::Hidden);
156
157  /// BlockExtractorPass - This pass is used by bugpoint to extract all blocks
158  /// from the module into their own functions except for those specified by the
159  /// BlocksToNotExtract list.
160  class BlockExtractorPass : public ModulePass {
161    void LoadFile(const char *Filename);
162
163    std::vector<BasicBlock*> BlocksToNotExtract;
164    std::vector<std::pair<std::string, std::string> > BlocksToNotExtractByName;
165  public:
166    static char ID; // Pass identification, replacement for typeid
167    explicit BlockExtractorPass(const std::vector<BasicBlock*> &B)
168      : ModulePass((intptr_t)&ID), BlocksToNotExtract(B) {
169      if (!BlockFile.empty())
170        LoadFile(BlockFile.c_str());
171    }
172    BlockExtractorPass() : ModulePass((intptr_t)&ID) {}
173
174    bool runOnModule(Module &M);
175  };
176
177  char BlockExtractorPass::ID = 0;
178  RegisterPass<BlockExtractorPass>
179  XX("extract-blocks", "Extract Basic Blocks From Module (for bugpoint use)");
180}
181
182// createBlockExtractorPass - This pass extracts all blocks (except those
183// specified in the argument list) from the functions in the module.
184//
185ModulePass *llvm::createBlockExtractorPass(const std::vector<BasicBlock*> &BTNE)
186{
187  return new BlockExtractorPass(BTNE);
188}
189
190void BlockExtractorPass::LoadFile(const char *Filename) {
191  // Load the BlockFile...
192  std::ifstream In(Filename);
193  if (!In.good()) {
194    cerr << "WARNING: BlockExtractor couldn't load file '" << Filename
195         << "'!\n";
196    return;
197  }
198  while (In) {
199    std::string FunctionName, BlockName;
200    In >> FunctionName;
201    In >> BlockName;
202    if (!BlockName.empty())
203      BlocksToNotExtractByName.push_back(
204          std::make_pair(FunctionName, BlockName));
205  }
206}
207
208bool BlockExtractorPass::runOnModule(Module &M) {
209  std::set<BasicBlock*> TranslatedBlocksToNotExtract;
210  for (unsigned i = 0, e = BlocksToNotExtract.size(); i != e; ++i) {
211    BasicBlock *BB = BlocksToNotExtract[i];
212    Function *F = BB->getParent();
213
214    // Map the corresponding function in this module.
215    Function *MF = M.getFunction(F->getName());
216    assert(MF->getFunctionType() == F->getFunctionType() && "Wrong function?");
217
218    // Figure out which index the basic block is in its function.
219    Function::iterator BBI = MF->begin();
220    std::advance(BBI, std::distance(F->begin(), Function::iterator(BB)));
221    TranslatedBlocksToNotExtract.insert(BBI);
222  }
223
224  while (!BlocksToNotExtractByName.empty()) {
225    // There's no way to find BBs by name without looking at every BB inside
226    // every Function. Fortunately, this is always empty except when used by
227    // bugpoint in which case correctness is more important than performance.
228
229    std::string &FuncName  = BlocksToNotExtractByName.back().first;
230    std::string &BlockName = BlocksToNotExtractByName.back().second;
231
232    for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI) {
233      Function &F = *FI;
234      if (F.getName() != FuncName) continue;
235
236      for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
237        BasicBlock &BB = *BI;
238        if (BB.getName() != BlockName) continue;
239
240        TranslatedBlocksToNotExtract.insert(BI);
241      }
242    }
243
244    BlocksToNotExtractByName.pop_back();
245  }
246
247  // Now that we know which blocks to not extract, figure out which ones we WANT
248  // to extract.
249  std::vector<BasicBlock*> BlocksToExtract;
250  for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
251    for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
252      if (!TranslatedBlocksToNotExtract.count(BB))
253        BlocksToExtract.push_back(BB);
254
255  for (unsigned i = 0, e = BlocksToExtract.size(); i != e; ++i)
256    ExtractBasicBlock(BlocksToExtract[i]);
257
258  return !BlocksToExtract.empty();
259}
260