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 #include "llvm/Transforms/IPO.h"
18 #include "llvm/Instructions.h"
19 #include "llvm/Module.h"
20 #include "llvm/Pass.h"
21 #include "llvm/Analysis/Dominators.h"
22 #include "llvm/Analysis/LoopInfo.h"
23 #include "llvm/Transforms/Scalar.h"
24 #include "llvm/Transforms/Utils/FunctionUtils.h"
25 #include "llvm/ADT/Statistic.h"
26 using namespace llvm;
27 
28 namespace {
29   Statistic<> NumExtracted("loop-extract", "Number of loops extracted");
30 
31   // FIXME: This is not a function pass, but the PassManager doesn't allow
32   // Module passes to require FunctionPasses, so we can't get loop info if we're
33   // not a function pass.
34   struct LoopExtractor : public FunctionPass {
35     unsigned NumLoops;
36 
37     LoopExtractor(unsigned numLoops = ~0) : NumLoops(numLoops) {}
38 
39     virtual bool runOnFunction(Function &F);
40 
41     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
42       AU.addRequiredID(BreakCriticalEdgesID);
43       AU.addRequiredID(LoopSimplifyID);
44       AU.addRequired<DominatorSet>();
45       AU.addRequired<LoopInfo>();
46     }
47   };
48 
49   RegisterOpt<LoopExtractor>
50   X("loop-extract", "Extract loops into new functions");
51 
52   /// SingleLoopExtractor - For bugpoint.
53   struct SingleLoopExtractor : public LoopExtractor {
54     SingleLoopExtractor() : LoopExtractor(1) {}
55   };
56 
57   RegisterOpt<SingleLoopExtractor>
58   Y("loop-extract-single", "Extract at most one loop into a new function");
59 } // End anonymous namespace
60 
61 // createLoopExtractorPass - This pass extracts all natural loops from the
62 // program into a function if it can.
63 //
64 FunctionPass *llvm::createLoopExtractorPass() { return new LoopExtractor(); }
65 
66 bool LoopExtractor::runOnFunction(Function &F) {
67   LoopInfo &LI = getAnalysis<LoopInfo>();
68 
69   // If this function has no loops, there is nothing to do.
70   if (LI.begin() == LI.end())
71     return false;
72 
73   DominatorSet &DS = getAnalysis<DominatorSet>();
74 
75   // If there is more than one top-level loop in this function, extract all of
76   // the loops.
77   bool Changed = false;
78   if (LI.end()-LI.begin() > 1) {
79     for (LoopInfo::iterator i = LI.begin(), e = LI.end(); i != e; ++i) {
80       if (NumLoops == 0) return Changed;
81       --NumLoops;
82       Changed |= ExtractLoop(DS, *i) != 0;
83       ++NumExtracted;
84     }
85   } else {
86     // Otherwise there is exactly one top-level loop.  If this function is more
87     // than a minimal wrapper around the loop, extract the loop.
88     Loop *TLL = *LI.begin();
89     bool ShouldExtractLoop = false;
90 
91     // Extract the loop if the entry block doesn't branch to the loop header.
92     TerminatorInst *EntryTI = F.getEntryBlock().getTerminator();
93     if (!isa<BranchInst>(EntryTI) ||
94         !cast<BranchInst>(EntryTI)->isUnconditional() ||
95         EntryTI->getSuccessor(0) != TLL->getHeader())
96       ShouldExtractLoop = true;
97     else {
98       // Check to see if any exits from the loop are more than just return
99       // blocks.
100       std::vector<BasicBlock*> ExitBlocks;
101       TLL->getExitBlocks(ExitBlocks);
102       for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
103         if (!isa<ReturnInst>(ExitBlocks[i]->getTerminator())) {
104           ShouldExtractLoop = true;
105           break;
106         }
107     }
108 
109     if (ShouldExtractLoop) {
110       if (NumLoops == 0) return Changed;
111       --NumLoops;
112       Changed |= ExtractLoop(DS, TLL) != 0;
113       ++NumExtracted;
114     } else {
115       // Okay, this function is a minimal container around the specified loop.
116       // If we extract the loop, we will continue to just keep extracting it
117       // infinitely... so don't extract it.  However, if the loop contains any
118       // subloops, extract them.
119       for (Loop::iterator i = TLL->begin(), e = TLL->end(); i != e; ++i) {
120         if (NumLoops == 0) return Changed;
121         --NumLoops;
122         Changed |= ExtractLoop(DS, *i) != 0;
123         ++NumExtracted;
124       }
125     }
126   }
127 
128   return Changed;
129 }
130 
131 // createSingleLoopExtractorPass - This pass extracts one natural loop from the
132 // program into a function if it can.  This is used by bugpoint.
133 //
134 FunctionPass *llvm::createSingleLoopExtractorPass() {
135   return new SingleLoopExtractor();
136 }
137 
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     std::vector<BasicBlock*> BlocksToNotExtract;
145   public:
146     BlockExtractorPass(std::vector<BasicBlock*> &B) : BlocksToNotExtract(B) {}
147     BlockExtractorPass() {}
148 
149     bool runOnModule(Module &M);
150   };
151   RegisterOpt<BlockExtractorPass>
152   XX("extract-blocks", "Extract Basic Blocks From Module (for bugpoint use)");
153 }
154 
155 // createBlockExtractorPass - This pass extracts all blocks (except those
156 // specified in the argument list) from the functions in the module.
157 //
158 ModulePass *llvm::createBlockExtractorPass(std::vector<BasicBlock*> &BTNE) {
159   return new BlockExtractorPass(BTNE);
160 }
161 
162 bool BlockExtractorPass::runOnModule(Module &M) {
163   std::set<BasicBlock*> TranslatedBlocksToNotExtract;
164   for (unsigned i = 0, e = BlocksToNotExtract.size(); i != e; ++i) {
165     BasicBlock *BB = BlocksToNotExtract[i];
166     Function *F = BB->getParent();
167 
168     // Map the corresponding function in this module.
169     Function *MF = M.getFunction(F->getName(), F->getFunctionType());
170 
171     // Figure out which index the basic block is in its function.
172     Function::iterator BBI = MF->begin();
173     std::advance(BBI, std::distance(F->begin(), Function::iterator(BB)));
174     TranslatedBlocksToNotExtract.insert(BBI);
175   }
176 
177   // Now that we know which blocks to not extract, figure out which ones we WANT
178   // to extract.
179   std::vector<BasicBlock*> BlocksToExtract;
180   for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
181     for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
182       if (!TranslatedBlocksToNotExtract.count(BB))
183         BlocksToExtract.push_back(BB);
184 
185   for (unsigned i = 0, e = BlocksToExtract.size(); i != e; ++i)
186     ExtractBasicBlock(BlocksToExtract[i]);
187 
188   return !BlocksToExtract.empty();
189 }
190