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/BasicBlockUtils.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 struct LoopExtractor : public LoopPass {
37 static char ID; // Pass identification, replacement for typeid
38 unsigned NumLoops;
39
LoopExtractor__anonaee8daa60111::LoopExtractor40 explicit LoopExtractor(unsigned numLoops = ~0)
41 : LoopPass(ID), NumLoops(numLoops) {
42 initializeLoopExtractorPass(*PassRegistry::getPassRegistry());
43 }
44
45 virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
46
getAnalysisUsage__anonaee8daa60111::LoopExtractor47 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
48 AU.addRequiredID(BreakCriticalEdgesID);
49 AU.addRequiredID(LoopSimplifyID);
50 AU.addRequired<DominatorTree>();
51 }
52 };
53 }
54
55 char LoopExtractor::ID = 0;
56 INITIALIZE_PASS_BEGIN(LoopExtractor, "loop-extract",
57 "Extract loops into new functions", false, false)
58 INITIALIZE_PASS_DEPENDENCY(BreakCriticalEdges)
59 INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
60 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
61 INITIALIZE_PASS_END(LoopExtractor, "loop-extract",
62 "Extract loops into new functions", false, false)
63
64 namespace {
65 /// SingleLoopExtractor - For bugpoint.
66 struct SingleLoopExtractor : public LoopExtractor {
67 static char ID; // Pass identification, replacement for typeid
SingleLoopExtractor__anonaee8daa60211::SingleLoopExtractor68 SingleLoopExtractor() : LoopExtractor(1) {}
69 };
70 } // End anonymous namespace
71
72 char SingleLoopExtractor::ID = 0;
73 INITIALIZE_PASS(SingleLoopExtractor, "loop-extract-single",
74 "Extract at most one loop into a new function", false, false)
75
76 // createLoopExtractorPass - This pass extracts all natural loops from the
77 // program into a function if it can.
78 //
createLoopExtractorPass()79 Pass *llvm::createLoopExtractorPass() { return new LoopExtractor(); }
80
runOnLoop(Loop * L,LPPassManager & LPM)81 bool LoopExtractor::runOnLoop(Loop *L, LPPassManager &LPM) {
82 // Only visit top-level loops.
83 if (L->getParentLoop())
84 return false;
85
86 // If LoopSimplify form is not available, stay out of trouble.
87 if (!L->isLoopSimplifyForm())
88 return false;
89
90 DominatorTree &DT = getAnalysis<DominatorTree>();
91 bool Changed = false;
92
93 // If there is more than one top-level loop in this function, extract all of
94 // the loops. Otherwise there is exactly one top-level loop; in this case if
95 // this function is more than a minimal wrapper around the loop, extract
96 // the loop.
97 bool ShouldExtractLoop = false;
98
99 // Extract the loop if the entry block doesn't branch to the loop header.
100 TerminatorInst *EntryTI =
101 L->getHeader()->getParent()->getEntryBlock().getTerminator();
102 if (!isa<BranchInst>(EntryTI) ||
103 !cast<BranchInst>(EntryTI)->isUnconditional() ||
104 EntryTI->getSuccessor(0) != L->getHeader()) {
105 ShouldExtractLoop = true;
106 } else {
107 // Check to see if any exits from the loop are more than just return
108 // blocks.
109 SmallVector<BasicBlock*, 8> ExitBlocks;
110 L->getExitBlocks(ExitBlocks);
111 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
112 if (!isa<ReturnInst>(ExitBlocks[i]->getTerminator())) {
113 ShouldExtractLoop = true;
114 break;
115 }
116 }
117
118 if (ShouldExtractLoop) {
119 // We must omit landing pads. Landing pads must accompany the invoke
120 // instruction. But this would result in a loop in the extracted
121 // function. An infinite cycle occurs when it tries to extract that loop as
122 // well.
123 SmallVector<BasicBlock*, 8> ExitBlocks;
124 L->getExitBlocks(ExitBlocks);
125 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
126 if (ExitBlocks[i]->isLandingPad()) {
127 ShouldExtractLoop = false;
128 break;
129 }
130 }
131
132 if (ShouldExtractLoop) {
133 if (NumLoops == 0) return Changed;
134 --NumLoops;
135 if (ExtractLoop(DT, L) != 0) {
136 Changed = true;
137 // After extraction, the loop is replaced by a function call, so
138 // we shouldn't try to run any more loop passes on it.
139 LPM.deleteLoopFromQueue(L);
140 }
141 ++NumExtracted;
142 }
143
144 return Changed;
145 }
146
147 // createSingleLoopExtractorPass - This pass extracts one natural loop from the
148 // program into a function if it can. This is used by bugpoint.
149 //
createSingleLoopExtractorPass()150 Pass *llvm::createSingleLoopExtractorPass() {
151 return new SingleLoopExtractor();
152 }
153
154
155 // BlockFile - A file which contains a list of blocks that should not be
156 // extracted.
157 static cl::opt<std::string>
158 BlockFile("extract-blocks-file", cl::value_desc("filename"),
159 cl::desc("A file containing list of basic blocks to not extract"),
160 cl::Hidden);
161
162 namespace {
163 /// BlockExtractorPass - This pass is used by bugpoint to extract all blocks
164 /// from the module into their own functions except for those specified by the
165 /// BlocksToNotExtract list.
166 class BlockExtractorPass : public ModulePass {
167 void LoadFile(const char *Filename);
168 void SplitLandingPadPreds(Function *F);
169
170 std::vector<BasicBlock*> BlocksToNotExtract;
171 std::vector<std::pair<std::string, std::string> > BlocksToNotExtractByName;
172 public:
173 static char ID; // Pass identification, replacement for typeid
BlockExtractorPass()174 BlockExtractorPass() : ModulePass(ID) {
175 if (!BlockFile.empty())
176 LoadFile(BlockFile.c_str());
177 }
178
179 bool runOnModule(Module &M);
180 };
181 }
182
183 char BlockExtractorPass::ID = 0;
184 INITIALIZE_PASS(BlockExtractorPass, "extract-blocks",
185 "Extract Basic Blocks From Module (for bugpoint use)",
186 false, false)
187
188 // createBlockExtractorPass - This pass extracts all blocks (except those
189 // specified in the argument list) from the functions in the module.
190 //
createBlockExtractorPass()191 ModulePass *llvm::createBlockExtractorPass() {
192 return new BlockExtractorPass();
193 }
194
LoadFile(const char * Filename)195 void BlockExtractorPass::LoadFile(const char *Filename) {
196 // Load the BlockFile...
197 std::ifstream In(Filename);
198 if (!In.good()) {
199 errs() << "WARNING: BlockExtractor couldn't load file '" << Filename
200 << "'!\n";
201 return;
202 }
203 while (In) {
204 std::string FunctionName, BlockName;
205 In >> FunctionName;
206 In >> BlockName;
207 if (!BlockName.empty())
208 BlocksToNotExtractByName.push_back(
209 std::make_pair(FunctionName, BlockName));
210 }
211 }
212
213 /// SplitLandingPadPreds - The landing pad needs to be extracted with the invoke
214 /// instruction. The critical edge breaker will refuse to break critical edges
215 /// to a landing pad. So do them here. After this method runs, all landing pads
216 /// should have only one predecessor.
SplitLandingPadPreds(Function * F)217 void BlockExtractorPass::SplitLandingPadPreds(Function *F) {
218 for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
219 InvokeInst *II = dyn_cast<InvokeInst>(I);
220 if (!II) continue;
221 BasicBlock *Parent = II->getParent();
222 BasicBlock *LPad = II->getUnwindDest();
223
224 // Look through the landing pad's predecessors. If one of them ends in an
225 // 'invoke', then we want to split the landing pad.
226 bool Split = false;
227 for (pred_iterator
228 PI = pred_begin(LPad), PE = pred_end(LPad); PI != PE; ++PI) {
229 BasicBlock *BB = *PI;
230 if (BB->isLandingPad() && BB != Parent &&
231 isa<InvokeInst>(Parent->getTerminator())) {
232 Split = true;
233 break;
234 }
235 }
236
237 if (!Split) continue;
238
239 SmallVector<BasicBlock*, 2> NewBBs;
240 SplitLandingPadPredecessors(LPad, Parent, ".1", ".2", 0, NewBBs);
241 }
242 }
243
runOnModule(Module & M)244 bool BlockExtractorPass::runOnModule(Module &M) {
245 std::set<BasicBlock*> TranslatedBlocksToNotExtract;
246 for (unsigned i = 0, e = BlocksToNotExtract.size(); i != e; ++i) {
247 BasicBlock *BB = BlocksToNotExtract[i];
248 Function *F = BB->getParent();
249
250 // Map the corresponding function in this module.
251 Function *MF = M.getFunction(F->getName());
252 assert(MF->getFunctionType() == F->getFunctionType() && "Wrong function?");
253
254 // Figure out which index the basic block is in its function.
255 Function::iterator BBI = MF->begin();
256 std::advance(BBI, std::distance(F->begin(), Function::iterator(BB)));
257 TranslatedBlocksToNotExtract.insert(BBI);
258 }
259
260 while (!BlocksToNotExtractByName.empty()) {
261 // There's no way to find BBs by name without looking at every BB inside
262 // every Function. Fortunately, this is always empty except when used by
263 // bugpoint in which case correctness is more important than performance.
264
265 std::string &FuncName = BlocksToNotExtractByName.back().first;
266 std::string &BlockName = BlocksToNotExtractByName.back().second;
267
268 for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI) {
269 Function &F = *FI;
270 if (F.getName() != FuncName) continue;
271
272 for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
273 BasicBlock &BB = *BI;
274 if (BB.getName() != BlockName) continue;
275
276 TranslatedBlocksToNotExtract.insert(BI);
277 }
278 }
279
280 BlocksToNotExtractByName.pop_back();
281 }
282
283 // Now that we know which blocks to not extract, figure out which ones we WANT
284 // to extract.
285 std::vector<BasicBlock*> BlocksToExtract;
286 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
287 SplitLandingPadPreds(&*F);
288 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
289 if (!TranslatedBlocksToNotExtract.count(BB))
290 BlocksToExtract.push_back(BB);
291 }
292
293 for (unsigned i = 0, e = BlocksToExtract.size(); i != e; ++i) {
294 SmallVector<BasicBlock*, 2> BlocksToExtractVec;
295 BlocksToExtractVec.push_back(BlocksToExtract[i]);
296 if (const InvokeInst *II =
297 dyn_cast<InvokeInst>(BlocksToExtract[i]->getTerminator()))
298 BlocksToExtractVec.push_back(II->getUnwindDest());
299 ExtractBasicBlock(BlocksToExtractVec);
300 }
301
302 return !BlocksToExtract.empty();
303 }
304