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#include "llvm/Transforms/IPO.h"
18#include "llvm/ADT/Statistic.h"
19#include "llvm/Analysis/LoopPass.h"
20#include "llvm/IR/Dominators.h"
21#include "llvm/IR/Instructions.h"
22#include "llvm/IR/Module.h"
23#include "llvm/Pass.h"
24#include "llvm/Support/CommandLine.h"
25#include "llvm/Transforms/Scalar.h"
26#include "llvm/Transforms/Utils/BasicBlockUtils.h"
27#include "llvm/Transforms/Utils/CodeExtractor.h"
28#include <fstream>
29#include <set>
30using namespace llvm;
31
32#define DEBUG_TYPE "loop-extract"
33
34STATISTIC(NumExtracted, "Number of loops extracted");
35
36namespace {
37  struct LoopExtractor : public LoopPass {
38    static char ID; // Pass identification, replacement for typeid
39    unsigned NumLoops;
40
41    explicit LoopExtractor(unsigned numLoops = ~0)
42      : LoopPass(ID), NumLoops(numLoops) {
43        initializeLoopExtractorPass(*PassRegistry::getPassRegistry());
44      }
45
46    bool runOnLoop(Loop *L, LPPassManager &) override;
47
48    void getAnalysisUsage(AnalysisUsage &AU) const override {
49      AU.addRequiredID(BreakCriticalEdgesID);
50      AU.addRequiredID(LoopSimplifyID);
51      AU.addRequired<DominatorTreeWrapperPass>();
52      AU.addRequired<LoopInfoWrapperPass>();
53    }
54  };
55}
56
57char LoopExtractor::ID = 0;
58INITIALIZE_PASS_BEGIN(LoopExtractor, "loop-extract",
59                      "Extract loops into new functions", false, false)
60INITIALIZE_PASS_DEPENDENCY(BreakCriticalEdges)
61INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
62INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
63INITIALIZE_PASS_END(LoopExtractor, "loop-extract",
64                    "Extract loops into new functions", false, false)
65
66namespace {
67  /// SingleLoopExtractor - For bugpoint.
68  struct SingleLoopExtractor : public LoopExtractor {
69    static char ID; // Pass identification, replacement for typeid
70    SingleLoopExtractor() : LoopExtractor(1) {}
71  };
72} // End anonymous namespace
73
74char SingleLoopExtractor::ID = 0;
75INITIALIZE_PASS(SingleLoopExtractor, "loop-extract-single",
76                "Extract at most one loop into a new function", false, false)
77
78// createLoopExtractorPass - This pass extracts all natural loops from the
79// program into a function if it can.
80//
81Pass *llvm::createLoopExtractorPass() { return new LoopExtractor(); }
82
83bool LoopExtractor::runOnLoop(Loop *L, LPPassManager &) {
84  if (skipLoop(L))
85    return false;
86
87  // Only visit top-level loops.
88  if (L->getParentLoop())
89    return false;
90
91  // If LoopSimplify form is not available, stay out of trouble.
92  if (!L->isLoopSimplifyForm())
93    return false;
94
95  DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
96  LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
97  bool Changed = false;
98
99  // If there is more than one top-level loop in this function, extract all of
100  // the loops. Otherwise there is exactly one top-level loop; in this case if
101  // this function is more than a minimal wrapper around the loop, extract
102  // the loop.
103  bool ShouldExtractLoop = false;
104
105  // Extract the loop if the entry block doesn't branch to the loop header.
106  TerminatorInst *EntryTI =
107    L->getHeader()->getParent()->getEntryBlock().getTerminator();
108  if (!isa<BranchInst>(EntryTI) ||
109      !cast<BranchInst>(EntryTI)->isUnconditional() ||
110      EntryTI->getSuccessor(0) != L->getHeader()) {
111    ShouldExtractLoop = true;
112  } else {
113    // Check to see if any exits from the loop are more than just return
114    // blocks.
115    SmallVector<BasicBlock*, 8> ExitBlocks;
116    L->getExitBlocks(ExitBlocks);
117    for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
118      if (!isa<ReturnInst>(ExitBlocks[i]->getTerminator())) {
119        ShouldExtractLoop = true;
120        break;
121      }
122  }
123
124  if (ShouldExtractLoop) {
125    // We must omit EH pads. EH pads must accompany the invoke
126    // instruction. But this would result in a loop in the extracted
127    // function. An infinite cycle occurs when it tries to extract that loop as
128    // well.
129    SmallVector<BasicBlock*, 8> ExitBlocks;
130    L->getExitBlocks(ExitBlocks);
131    for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
132      if (ExitBlocks[i]->isEHPad()) {
133        ShouldExtractLoop = false;
134        break;
135      }
136  }
137
138  if (ShouldExtractLoop) {
139    if (NumLoops == 0) return Changed;
140    --NumLoops;
141    CodeExtractor Extractor(DT, *L);
142    if (Extractor.extractCodeRegion() != nullptr) {
143      Changed = true;
144      // After extraction, the loop is replaced by a function call, so
145      // we shouldn't try to run any more loop passes on it.
146      LI.markAsRemoved(L);
147    }
148    ++NumExtracted;
149  }
150
151  return Changed;
152}
153
154// createSingleLoopExtractorPass - This pass extracts one natural loop from the
155// program into a function if it can.  This is used by bugpoint.
156//
157Pass *llvm::createSingleLoopExtractorPass() {
158  return new SingleLoopExtractor();
159}
160
161
162// BlockFile - A file which contains a list of blocks that should not be
163// extracted.
164static cl::opt<std::string>
165BlockFile("extract-blocks-file", cl::value_desc("filename"),
166          cl::desc("A file containing list of basic blocks to not extract"),
167          cl::Hidden);
168
169namespace {
170  /// BlockExtractorPass - This pass is used by bugpoint to extract all blocks
171  /// from the module into their own functions except for those specified by the
172  /// BlocksToNotExtract list.
173  class BlockExtractorPass : public ModulePass {
174    void LoadFile(const char *Filename);
175    void SplitLandingPadPreds(Function *F);
176
177    std::vector<BasicBlock*> BlocksToNotExtract;
178    std::vector<std::pair<std::string, std::string> > BlocksToNotExtractByName;
179  public:
180    static char ID; // Pass identification, replacement for typeid
181    BlockExtractorPass() : ModulePass(ID) {
182      if (!BlockFile.empty())
183        LoadFile(BlockFile.c_str());
184    }
185
186    bool runOnModule(Module &M) override;
187  };
188}
189
190char BlockExtractorPass::ID = 0;
191INITIALIZE_PASS(BlockExtractorPass, "extract-blocks",
192                "Extract Basic Blocks From Module (for bugpoint use)",
193                false, false)
194
195// createBlockExtractorPass - This pass extracts all blocks (except those
196// specified in the argument list) from the functions in the module.
197//
198ModulePass *llvm::createBlockExtractorPass() {
199  return new BlockExtractorPass();
200}
201
202void BlockExtractorPass::LoadFile(const char *Filename) {
203  // Load the BlockFile...
204  std::ifstream In(Filename);
205  if (!In.good()) {
206    errs() << "WARNING: BlockExtractor couldn't load file '" << Filename
207           << "'!\n";
208    return;
209  }
210  while (In) {
211    std::string FunctionName, BlockName;
212    In >> FunctionName;
213    In >> BlockName;
214    if (!BlockName.empty())
215      BlocksToNotExtractByName.push_back(
216          std::make_pair(FunctionName, BlockName));
217  }
218}
219
220/// SplitLandingPadPreds - The landing pad needs to be extracted with the invoke
221/// instruction. The critical edge breaker will refuse to break critical edges
222/// to a landing pad. So do them here. After this method runs, all landing pads
223/// should have only one predecessor.
224void BlockExtractorPass::SplitLandingPadPreds(Function *F) {
225  for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
226    InvokeInst *II = dyn_cast<InvokeInst>(I);
227    if (!II) continue;
228    BasicBlock *Parent = II->getParent();
229    BasicBlock *LPad = II->getUnwindDest();
230
231    // Look through the landing pad's predecessors. If one of them ends in an
232    // 'invoke', then we want to split the landing pad.
233    bool Split = false;
234    for (pred_iterator
235           PI = pred_begin(LPad), PE = pred_end(LPad); PI != PE; ++PI) {
236      BasicBlock *BB = *PI;
237      if (BB->isLandingPad() && BB != Parent &&
238          isa<InvokeInst>(Parent->getTerminator())) {
239        Split = true;
240        break;
241      }
242    }
243
244    if (!Split) continue;
245
246    SmallVector<BasicBlock*, 2> NewBBs;
247    SplitLandingPadPredecessors(LPad, Parent, ".1", ".2", NewBBs);
248  }
249}
250
251bool BlockExtractorPass::runOnModule(Module &M) {
252  if (skipModule(M))
253    return false;
254
255  std::set<BasicBlock*> TranslatedBlocksToNotExtract;
256  for (unsigned i = 0, e = BlocksToNotExtract.size(); i != e; ++i) {
257    BasicBlock *BB = BlocksToNotExtract[i];
258    Function *F = BB->getParent();
259
260    // Map the corresponding function in this module.
261    Function *MF = M.getFunction(F->getName());
262    assert(MF->getFunctionType() == F->getFunctionType() && "Wrong function?");
263
264    // Figure out which index the basic block is in its function.
265    Function::iterator BBI = MF->begin();
266    std::advance(BBI, std::distance(F->begin(), Function::iterator(BB)));
267    TranslatedBlocksToNotExtract.insert(&*BBI);
268  }
269
270  while (!BlocksToNotExtractByName.empty()) {
271    // There's no way to find BBs by name without looking at every BB inside
272    // every Function. Fortunately, this is always empty except when used by
273    // bugpoint in which case correctness is more important than performance.
274
275    std::string &FuncName  = BlocksToNotExtractByName.back().first;
276    std::string &BlockName = BlocksToNotExtractByName.back().second;
277
278    for (Function &F : M) {
279      if (F.getName() != FuncName) continue;
280
281      for (BasicBlock &BB : F) {
282        if (BB.getName() != BlockName) continue;
283
284        TranslatedBlocksToNotExtract.insert(&BB);
285      }
286    }
287
288    BlocksToNotExtractByName.pop_back();
289  }
290
291  // Now that we know which blocks to not extract, figure out which ones we WANT
292  // to extract.
293  std::vector<BasicBlock*> BlocksToExtract;
294  for (Function &F : M) {
295    SplitLandingPadPreds(&F);
296    for (BasicBlock &BB : F)
297      if (!TranslatedBlocksToNotExtract.count(&BB))
298        BlocksToExtract.push_back(&BB);
299  }
300
301  for (BasicBlock *BlockToExtract : BlocksToExtract) {
302    SmallVector<BasicBlock*, 2> BlocksToExtractVec;
303    BlocksToExtractVec.push_back(BlockToExtract);
304    if (const InvokeInst *II =
305            dyn_cast<InvokeInst>(BlockToExtract->getTerminator()))
306      BlocksToExtractVec.push_back(II->getUnwindDest());
307    CodeExtractor(BlocksToExtractVec).extractCodeRegion();
308  }
309
310  return !BlocksToExtract.empty();
311}
312