LoopExtractor.cpp revision d720670393434effa832b686b4a482b736bd9c4d 
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>
30using namespace llvm;
31
32STATISTIC(NumExtracted, "Number of loops extracted");
33
34namespace {
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
42    virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
43
44    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
45      AU.addRequiredID(BreakCriticalEdgesID);
46      AU.addRequiredID(LoopSimplifyID);
47      AU.addRequired<DominatorTree>();
48    }
49  };
50}
51
52char LoopExtractor::ID = 0;
53INITIALIZE_PASS(LoopExtractor, "loop-extract",
54                "Extract loops into new functions", false, false);
55
56namespace {
57  /// SingleLoopExtractor - For bugpoint.
58  struct SingleLoopExtractor : public LoopExtractor {
59    static char ID; // Pass identification, replacement for typeid
60    SingleLoopExtractor() : LoopExtractor(1) {}
61  };
62} // End anonymous namespace
63
64char SingleLoopExtractor::ID = 0;
65INITIALIZE_PASS(SingleLoopExtractor, "loop-extract-single",
66                "Extract at most one loop into a new function", false, false);
67
68// createLoopExtractorPass - This pass extracts all natural loops from the
69// program into a function if it can.
70//
71Pass *llvm::createLoopExtractorPass() { return new LoopExtractor(); }
72
73bool LoopExtractor::runOnLoop(Loop *L, LPPassManager &LPM) {
74  // Only visit top-level loops.
75  if (L->getParentLoop())
76    return false;
77
78  // If LoopSimplify form is not available, stay out of trouble.
79  if (!L->isLoopSimplifyForm())
80    return false;
81
82  DominatorTree &DT = getAnalysis<DominatorTree>();
83  bool Changed = false;
84
85  // If there is more than one top-level loop in this function, extract all of
86  // the loops. Otherwise there is exactly one top-level loop; in this case if
87  // this function is more than a minimal wrapper around the loop, extract
88  // the loop.
89  bool ShouldExtractLoop = false;
90
91  // Extract the loop if the entry block doesn't branch to the loop header.
92  TerminatorInst *EntryTI =
93    L->getHeader()->getParent()->getEntryBlock().getTerminator();
94  if (!isa<BranchInst>(EntryTI) ||
95      !cast<BranchInst>(EntryTI)->isUnconditional() ||
96      EntryTI->getSuccessor(0) != L->getHeader())
97    ShouldExtractLoop = true;
98  else {
99    // Check to see if any exits from the loop are more than just return
100    // blocks.
101    SmallVector<BasicBlock*, 8> ExitBlocks;
102    L->getExitBlocks(ExitBlocks);
103    for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
104      if (!isa<ReturnInst>(ExitBlocks[i]->getTerminator())) {
105        ShouldExtractLoop = true;
106        break;
107      }
108  }
109  if (ShouldExtractLoop) {
110    if (NumLoops == 0) return Changed;
111    --NumLoops;
112    if (ExtractLoop(DT, L) != 0) {
113      Changed = true;
114      // After extraction, the loop is replaced by a function call, so
115      // we shouldn't try to run any more loop passes on it.
116      LPM.deleteLoopFromQueue(L);
117    }
118    ++NumExtracted;
119  }
120
121  return Changed;
122}
123
124// createSingleLoopExtractorPass - This pass extracts one natural loop from the
125// program into a function if it can.  This is used by bugpoint.
126//
127Pass *llvm::createSingleLoopExtractorPass() {
128  return new SingleLoopExtractor();
129}
130
131
132// BlockFile - A file which contains a list of blocks that should not be
133// extracted.
134static cl::opt<std::string>
135BlockFile("extract-blocks-file", cl::value_desc("filename"),
136          cl::desc("A file containing list of basic blocks to not extract"),
137          cl::Hidden);
138
139namespace {
140  /// BlockExtractorPass - This pass is used by bugpoint to extract all blocks
141  /// from the module into their own functions except for those specified by the
142  /// BlocksToNotExtract list.
143  class BlockExtractorPass : public ModulePass {
144    void LoadFile(const char *Filename);
145
146    std::vector<BasicBlock*> BlocksToNotExtract;
147    std::vector<std::pair<std::string, std::string> > BlocksToNotExtractByName;
148  public:
149    static char ID; // Pass identification, replacement for typeid
150    BlockExtractorPass() : ModulePass(&ID) {
151      if (!BlockFile.empty())
152        LoadFile(BlockFile.c_str());
153    }
154
155    bool runOnModule(Module &M);
156  };
157}
158
159char BlockExtractorPass::ID = 0;
160INITIALIZE_PASS(BlockExtractorPass, "extract-blocks",
161                "Extract Basic Blocks From Module (for bugpoint use)",
162                false, false);
163
164// createBlockExtractorPass - This pass extracts all blocks (except those
165// specified in the argument list) from the functions in the module.
166//
167ModulePass *llvm::createBlockExtractorPass()
168{
169  return new BlockExtractorPass();
170}
171
172void BlockExtractorPass::LoadFile(const char *Filename) {
173  // Load the BlockFile...
174  std::ifstream In(Filename);
175  if (!In.good()) {
176    errs() << "WARNING: BlockExtractor couldn't load file '" << Filename
177           << "'!\n";
178    return;
179  }
180  while (In) {
181    std::string FunctionName, BlockName;
182    In >> FunctionName;
183    In >> BlockName;
184    if (!BlockName.empty())
185      BlocksToNotExtractByName.push_back(
186          std::make_pair(FunctionName, BlockName));
187  }
188}
189
190bool BlockExtractorPass::runOnModule(Module &M) {
191  std::set<BasicBlock*> TranslatedBlocksToNotExtract;
192  for (unsigned i = 0, e = BlocksToNotExtract.size(); i != e; ++i) {
193    BasicBlock *BB = BlocksToNotExtract[i];
194    Function *F = BB->getParent();
195
196    // Map the corresponding function in this module.
197    Function *MF = M.getFunction(F->getName());
198    assert(MF->getFunctionType() == F->getFunctionType() && "Wrong function?");
199
200    // Figure out which index the basic block is in its function.
201    Function::iterator BBI = MF->begin();
202    std::advance(BBI, std::distance(F->begin(), Function::iterator(BB)));
203    TranslatedBlocksToNotExtract.insert(BBI);
204  }
205
206  while (!BlocksToNotExtractByName.empty()) {
207    // There's no way to find BBs by name without looking at every BB inside
208    // every Function. Fortunately, this is always empty except when used by
209    // bugpoint in which case correctness is more important than performance.
210
211    std::string &FuncName  = BlocksToNotExtractByName.back().first;
212    std::string &BlockName = BlocksToNotExtractByName.back().second;
213
214    for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI) {
215      Function &F = *FI;
216      if (F.getName() != FuncName) continue;
217
218      for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
219        BasicBlock &BB = *BI;
220        if (BB.getName() != BlockName) continue;
221
222        TranslatedBlocksToNotExtract.insert(BI);
223      }
224    }
225
226    BlocksToNotExtractByName.pop_back();
227  }
228
229  // Now that we know which blocks to not extract, figure out which ones we WANT
230  // to extract.
231  std::vector<BasicBlock*> BlocksToExtract;
232  for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
233    for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
234      if (!TranslatedBlocksToNotExtract.count(BB))
235        BlocksToExtract.push_back(BB);
236
237  for (unsigned i = 0, e = BlocksToExtract.size(); i != e; ++i)
238    ExtractBasicBlock(BlocksToExtract[i]);
239
240  return !BlocksToExtract.empty();
241}
242