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>
30 using namespace llvm;
31 
32 STATISTIC(NumExtracted, "Number of loops extracted");
33 
34 namespace {
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 
52 char LoopExtractor::ID = 0;
53 INITIALIZE_PASS(LoopExtractor, "loop-extract",
54                 "Extract loops into new functions", false, false);
55 
56 namespace {
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 
64 char SingleLoopExtractor::ID = 0;
65 INITIALIZE_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 //
71 Pass *llvm::createLoopExtractorPass() { return new LoopExtractor(); }
72 
73 bool 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 //
127 Pass *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.
134 static cl::opt<std::string>
135 BlockFile("extract-blocks-file", cl::value_desc("filename"),
136           cl::desc("A file containing list of basic blocks to not extract"),
137           cl::Hidden);
138 
139 namespace {
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 
159 char BlockExtractorPass::ID = 0;
160 INITIALIZE_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 //
167 ModulePass *llvm::createBlockExtractorPass()
168 {
169   return new BlockExtractorPass();
170 }
171 
172 void 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 
190 bool 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