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>
31 using namespace llvm;
32 
33 STATISTIC(NumExtracted, "Number of loops extracted");
34 
35 namespace {
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(&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 
57 char LoopExtractor::ID = 0;
58 static RegisterPass<LoopExtractor>
59 X("loop-extract", "Extract loops into new functions");
60 
61 namespace {
62   /// SingleLoopExtractor - For bugpoint.
63   struct SingleLoopExtractor : public LoopExtractor {
64     static char ID; // Pass identification, replacement for typeid
65     SingleLoopExtractor() : LoopExtractor(1) {}
66   };
67 } // End anonymous namespace
68 
69 char SingleLoopExtractor::ID = 0;
70 static RegisterPass<SingleLoopExtractor>
71 Y("loop-extract-single", "Extract at most one loop into a new function");
72 
73 // createLoopExtractorPass - This pass extracts all natural loops from the
74 // program into a function if it can.
75 //
76 FunctionPass *llvm::createLoopExtractorPass() { return new LoopExtractor(); }
77 
78 bool LoopExtractor::runOnFunction(Function &F) {
79   LoopInfo &LI = getAnalysis<LoopInfo>();
80 
81   // If this function has no loops, there is nothing to do.
82   if (LI.empty())
83     return false;
84 
85   DominatorTree &DT = getAnalysis<DominatorTree>();
86 
87   // If there is more than one top-level loop in this function, extract all of
88   // the loops.
89   bool Changed = false;
90   if (LI.end()-LI.begin() > 1) {
91     for (LoopInfo::iterator i = LI.begin(), e = LI.end(); i != e; ++i) {
92       if (NumLoops == 0) return Changed;
93       --NumLoops;
94       Changed |= ExtractLoop(DT, *i) != 0;
95       ++NumExtracted;
96     }
97   } else {
98     // Otherwise there is exactly one top-level loop.  If this function is more
99     // than a minimal wrapper around the loop, extract the loop.
100     Loop *TLL = *LI.begin();
101     bool ShouldExtractLoop = false;
102 
103     // Extract the loop if the entry block doesn't branch to the loop header.
104     TerminatorInst *EntryTI = F.getEntryBlock().getTerminator();
105     if (!isa<BranchInst>(EntryTI) ||
106         !cast<BranchInst>(EntryTI)->isUnconditional() ||
107         EntryTI->getSuccessor(0) != TLL->getHeader())
108       ShouldExtractLoop = true;
109     else {
110       // Check to see if any exits from the loop are more than just return
111       // blocks.
112       SmallVector<BasicBlock*, 8> ExitBlocks;
113       TLL->getExitBlocks(ExitBlocks);
114       for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
115         if (!isa<ReturnInst>(ExitBlocks[i]->getTerminator())) {
116           ShouldExtractLoop = true;
117           break;
118         }
119     }
120 
121     if (ShouldExtractLoop) {
122       if (NumLoops == 0) return Changed;
123       --NumLoops;
124       Changed |= ExtractLoop(DT, TLL) != 0;
125       ++NumExtracted;
126     } else {
127       // Okay, this function is a minimal container around the specified loop.
128       // If we extract the loop, we will continue to just keep extracting it
129       // infinitely... so don't extract it.  However, if the loop contains any
130       // subloops, extract them.
131       for (Loop::iterator i = TLL->begin(), e = TLL->end(); i != e; ++i) {
132         if (NumLoops == 0) return Changed;
133         --NumLoops;
134         Changed |= ExtractLoop(DT, *i) != 0;
135         ++NumExtracted;
136       }
137     }
138   }
139 
140   return Changed;
141 }
142 
143 // createSingleLoopExtractorPass - This pass extracts one natural loop from the
144 // program into a function if it can.  This is used by bugpoint.
145 //
146 FunctionPass *llvm::createSingleLoopExtractorPass() {
147   return new SingleLoopExtractor();
148 }
149 
150 
151 // BlockFile - A file which contains a list of blocks that should not be
152 // extracted.
153 static cl::opt<std::string>
154 BlockFile("extract-blocks-file", cl::value_desc("filename"),
155           cl::desc("A file containing list of basic blocks to not extract"),
156           cl::Hidden);
157 
158 namespace {
159   /// BlockExtractorPass - This pass is used by bugpoint to extract all blocks
160   /// from the module into their own functions except for those specified by the
161   /// BlocksToNotExtract list.
162   class BlockExtractorPass : public ModulePass {
163     void LoadFile(const char *Filename);
164 
165     std::vector<BasicBlock*> BlocksToNotExtract;
166     std::vector<std::pair<std::string, std::string> > BlocksToNotExtractByName;
167   public:
168     static char ID; // Pass identification, replacement for typeid
169     explicit BlockExtractorPass(const std::vector<BasicBlock*> &B)
170       : ModulePass(&ID), BlocksToNotExtract(B) {
171       if (!BlockFile.empty())
172         LoadFile(BlockFile.c_str());
173     }
174     BlockExtractorPass() : ModulePass(&ID) {}
175 
176     bool runOnModule(Module &M);
177   };
178 }
179 
180 char BlockExtractorPass::ID = 0;
181 static RegisterPass<BlockExtractorPass>
182 XX("extract-blocks", "Extract Basic Blocks From Module (for bugpoint use)");
183 
184 // createBlockExtractorPass - This pass extracts all blocks (except those
185 // specified in the argument list) from the functions in the module.
186 //
187 ModulePass *llvm::createBlockExtractorPass(const std::vector<BasicBlock*> &BTNE)
188 {
189   return new BlockExtractorPass(BTNE);
190 }
191 
192 void BlockExtractorPass::LoadFile(const char *Filename) {
193   // Load the BlockFile...
194   std::ifstream In(Filename);
195   if (!In.good()) {
196     cerr << "WARNING: BlockExtractor couldn't load file '" << Filename
197          << "'!\n";
198     return;
199   }
200   while (In) {
201     std::string FunctionName, BlockName;
202     In >> FunctionName;
203     In >> BlockName;
204     if (!BlockName.empty())
205       BlocksToNotExtractByName.push_back(
206           std::make_pair(FunctionName, BlockName));
207   }
208 }
209 
210 bool BlockExtractorPass::runOnModule(Module &M) {
211   std::set<BasicBlock*> TranslatedBlocksToNotExtract;
212   for (unsigned i = 0, e = BlocksToNotExtract.size(); i != e; ++i) {
213     BasicBlock *BB = BlocksToNotExtract[i];
214     Function *F = BB->getParent();
215 
216     // Map the corresponding function in this module.
217     Function *MF = M.getFunction(F->getName());
218     assert(MF->getFunctionType() == F->getFunctionType() && "Wrong function?");
219 
220     // Figure out which index the basic block is in its function.
221     Function::iterator BBI = MF->begin();
222     std::advance(BBI, std::distance(F->begin(), Function::iterator(BB)));
223     TranslatedBlocksToNotExtract.insert(BBI);
224   }
225 
226   while (!BlocksToNotExtractByName.empty()) {
227     // There's no way to find BBs by name without looking at every BB inside
228     // every Function. Fortunately, this is always empty except when used by
229     // bugpoint in which case correctness is more important than performance.
230 
231     std::string &FuncName  = BlocksToNotExtractByName.back().first;
232     std::string &BlockName = BlocksToNotExtractByName.back().second;
233 
234     for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI) {
235       Function &F = *FI;
236       if (F.getName() != FuncName) continue;
237 
238       for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
239         BasicBlock &BB = *BI;
240         if (BB.getName() != BlockName) continue;
241 
242         TranslatedBlocksToNotExtract.insert(BI);
243       }
244     }
245 
246     BlocksToNotExtractByName.pop_back();
247   }
248 
249   // Now that we know which blocks to not extract, figure out which ones we WANT
250   // to extract.
251   std::vector<BasicBlock*> BlocksToExtract;
252   for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
253     for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
254       if (!TranslatedBlocksToNotExtract.count(BB))
255         BlocksToExtract.push_back(BB);
256 
257   for (unsigned i = 0, e = BlocksToExtract.size(); i != e; ++i)
258     ExtractBasicBlock(BlocksToExtract[i]);
259 
260   return !BlocksToExtract.empty();
261 }
262