LoopExtractor.cpp revision 52909454c479c63c49a3386059a5ad58bbcc8b97 
1//===- LoopExtractor.cpp - Extract each loop into a new function ----------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file was developed by the LLVM research group and is distributed under
6// the University of Illinois Open Source 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/Compiler.h"
25#include "llvm/Transforms/Scalar.h"
26#include "llvm/Transforms/Utils/FunctionUtils.h"
27#include "llvm/ADT/Statistic.h"
28using namespace llvm;
29
30STATISTIC(NumExtracted, "Number of loops extracted");
31
32namespace {
33  // FIXME: This is not a function pass, but the PassManager doesn't allow
34  // Module passes to require FunctionPasses, so we can't get loop info if we're
35  // not a function pass.
36  struct VISIBILITY_HIDDEN LoopExtractor : public FunctionPass {
37    static char ID; // Pass identification, replacement for typeid
38    unsigned NumLoops;
39
40    explicit LoopExtractor(unsigned numLoops = ~0)
41      : FunctionPass((intptr_t)&ID), NumLoops(numLoops) {}
42
43    virtual bool runOnFunction(Function &F);
44
45    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
46      AU.addRequiredID(BreakCriticalEdgesID);
47      AU.addRequiredID(LoopSimplifyID);
48      AU.addRequired<DominatorTree>();
49      AU.addRequired<LoopInfo>();
50    }
51  };
52
53  char LoopExtractor::ID = 0;
54  RegisterPass<LoopExtractor>
55  X("loop-extract", "Extract loops into new functions");
56
57  /// SingleLoopExtractor - For bugpoint.
58  struct SingleLoopExtractor : public LoopExtractor {
59    static char ID; // Pass identification, replacement for typeid
60    SingleLoopExtractor() : LoopExtractor(1) {}
61  };
62
63  char SingleLoopExtractor::ID = 0;
64  RegisterPass<SingleLoopExtractor>
65  Y("loop-extract-single", "Extract at most one loop into a new function");
66} // End anonymous namespace
67
68// createLoopExtractorPass - This pass extracts all natural loops from the
69// program into a function if it can.
70//
71FunctionPass *llvm::createLoopExtractorPass() { return new LoopExtractor(); }
72
73bool LoopExtractor::runOnFunction(Function &F) {
74  LoopInfo &LI = getAnalysis<LoopInfo>();
75
76  // If this function has no loops, there is nothing to do.
77  if (LI.begin() == LI.end())
78    return false;
79
80  DominatorTree &DT = getAnalysis<DominatorTree>();
81
82  // If there is more than one top-level loop in this function, extract all of
83  // the loops.
84  bool Changed = false;
85  if (LI.end()-LI.begin() > 1) {
86    for (LoopInfo::iterator i = LI.begin(), e = LI.end(); i != e; ++i) {
87      if (NumLoops == 0) return Changed;
88      --NumLoops;
89      Changed |= ExtractLoop(DT, *i) != 0;
90      ++NumExtracted;
91    }
92  } else {
93    // Otherwise there is exactly one top-level loop.  If this function is more
94    // than a minimal wrapper around the loop, extract the loop.
95    Loop *TLL = *LI.begin();
96    bool ShouldExtractLoop = false;
97
98    // Extract the loop if the entry block doesn't branch to the loop header.
99    TerminatorInst *EntryTI = F.getEntryBlock().getTerminator();
100    if (!isa<BranchInst>(EntryTI) ||
101        !cast<BranchInst>(EntryTI)->isUnconditional() ||
102        EntryTI->getSuccessor(0) != TLL->getHeader())
103      ShouldExtractLoop = true;
104    else {
105      // Check to see if any exits from the loop are more than just return
106      // blocks.
107      SmallVector<BasicBlock*, 8> ExitBlocks;
108      TLL->getExitBlocks(ExitBlocks);
109      for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
110        if (!isa<ReturnInst>(ExitBlocks[i]->getTerminator())) {
111          ShouldExtractLoop = true;
112          break;
113        }
114    }
115
116    if (ShouldExtractLoop) {
117      if (NumLoops == 0) return Changed;
118      --NumLoops;
119      Changed |= ExtractLoop(DT, TLL) != 0;
120      ++NumExtracted;
121    } else {
122      // Okay, this function is a minimal container around the specified loop.
123      // If we extract the loop, we will continue to just keep extracting it
124      // infinitely... so don't extract it.  However, if the loop contains any
125      // subloops, extract them.
126      for (Loop::iterator i = TLL->begin(), e = TLL->end(); i != e; ++i) {
127        if (NumLoops == 0) return Changed;
128        --NumLoops;
129        Changed |= ExtractLoop(DT, *i) != 0;
130        ++NumExtracted;
131      }
132    }
133  }
134
135  return Changed;
136}
137
138// createSingleLoopExtractorPass - This pass extracts one natural loop from the
139// program into a function if it can.  This is used by bugpoint.
140//
141FunctionPass *llvm::createSingleLoopExtractorPass() {
142  return new SingleLoopExtractor();
143}
144
145
146namespace {
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    std::vector<BasicBlock*> BlocksToNotExtract;
152  public:
153    static char ID; // Pass identification, replacement for typeid
154    explicit BlockExtractorPass(const std::vector<BasicBlock*> &B)
155      : ModulePass((intptr_t)&ID), BlocksToNotExtract(B) {}
156    BlockExtractorPass() : ModulePass((intptr_t)&ID) {}
157
158    bool runOnModule(Module &M);
159  };
160
161  char BlockExtractorPass::ID = 0;
162  RegisterPass<BlockExtractorPass>
163  XX("extract-blocks", "Extract Basic Blocks From Module (for bugpoint use)");
164}
165
166// createBlockExtractorPass - This pass extracts all blocks (except those
167// specified in the argument list) from the functions in the module.
168//
169ModulePass *llvm::createBlockExtractorPass(const std::vector<BasicBlock*> &BTNE)
170{
171  return new BlockExtractorPass(BTNE);
172}
173
174bool BlockExtractorPass::runOnModule(Module &M) {
175  std::set<BasicBlock*> TranslatedBlocksToNotExtract;
176  for (unsigned i = 0, e = BlocksToNotExtract.size(); i != e; ++i) {
177    BasicBlock *BB = BlocksToNotExtract[i];
178    Function *F = BB->getParent();
179
180    // Map the corresponding function in this module.
181    Function *MF = M.getFunction(F->getName());
182    assert(MF->getFunctionType() == F->getFunctionType() && "Wrong function?");
183
184    // Figure out which index the basic block is in its function.
185    Function::iterator BBI = MF->begin();
186    std::advance(BBI, std::distance(F->begin(), Function::iterator(BB)));
187    TranslatedBlocksToNotExtract.insert(BBI);
188  }
189
190  // Now that we know which blocks to not extract, figure out which ones we WANT
191  // to extract.
192  std::vector<BasicBlock*> BlocksToExtract;
193  for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
194    for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
195      if (!TranslatedBlocksToNotExtract.count(BB))
196        BlocksToExtract.push_back(BB);
197
198  for (unsigned i = 0, e = BlocksToExtract.size(); i != e; ++i)
199    ExtractBasicBlock(BlocksToExtract[i]);
200
201  return !BlocksToExtract.empty();
202}
203