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