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>
30 using namespace llvm;
31
32 #define DEBUG_TYPE "loop-extract"
33
34 STATISTIC(NumExtracted, "Number of loops extracted");
35
36 namespace {
37 struct LoopExtractor : public LoopPass {
38 static char ID; // Pass identification, replacement for typeid
39 unsigned NumLoops;
40
LoopExtractor__anoneb02617d0111::LoopExtractor41 explicit LoopExtractor(unsigned numLoops = ~0)
42 : LoopPass(ID), NumLoops(numLoops) {
43 initializeLoopExtractorPass(*PassRegistry::getPassRegistry());
44 }
45
46 bool runOnLoop(Loop *L, LPPassManager &) override;
47
getAnalysisUsage__anoneb02617d0111::LoopExtractor48 void getAnalysisUsage(AnalysisUsage &AU) const override {
49 AU.addRequiredID(BreakCriticalEdgesID);
50 AU.addRequiredID(LoopSimplifyID);
51 AU.addRequired<DominatorTreeWrapperPass>();
52 AU.addRequired<LoopInfoWrapperPass>();
53 }
54 };
55 }
56
57 char LoopExtractor::ID = 0;
58 INITIALIZE_PASS_BEGIN(LoopExtractor, "loop-extract",
59 "Extract loops into new functions", false, false)
60 INITIALIZE_PASS_DEPENDENCY(BreakCriticalEdges)
61 INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
62 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
63 INITIALIZE_PASS_END(LoopExtractor, "loop-extract",
64 "Extract loops into new functions", false, false)
65
66 namespace {
67 /// SingleLoopExtractor - For bugpoint.
68 struct SingleLoopExtractor : public LoopExtractor {
69 static char ID; // Pass identification, replacement for typeid
SingleLoopExtractor__anoneb02617d0211::SingleLoopExtractor70 SingleLoopExtractor() : LoopExtractor(1) {}
71 };
72 } // End anonymous namespace
73
74 char SingleLoopExtractor::ID = 0;
75 INITIALIZE_PASS(SingleLoopExtractor, "loop-extract-single",
76 "Extract at most one loop into a new function", false, false)
77
78 // createLoopExtractorPass - This pass extracts all natural loops from the
79 // program into a function if it can.
80 //
createLoopExtractorPass()81 Pass *llvm::createLoopExtractorPass() { return new LoopExtractor(); }
82
runOnLoop(Loop * L,LPPassManager &)83 bool LoopExtractor::runOnLoop(Loop *L, LPPassManager &) {
84 if (skipOptnoneFunction(L))
85 return false;
86
87 // Only visit top-level loops.
88 if (L->getParentLoop())
89 return false;
90
91 // If LoopSimplify form is not available, stay out of trouble.
92 if (!L->isLoopSimplifyForm())
93 return false;
94
95 DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
96 LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
97 bool Changed = false;
98
99 // If there is more than one top-level loop in this function, extract all of
100 // the loops. Otherwise there is exactly one top-level loop; in this case if
101 // this function is more than a minimal wrapper around the loop, extract
102 // the loop.
103 bool ShouldExtractLoop = false;
104
105 // Extract the loop if the entry block doesn't branch to the loop header.
106 TerminatorInst *EntryTI =
107 L->getHeader()->getParent()->getEntryBlock().getTerminator();
108 if (!isa<BranchInst>(EntryTI) ||
109 !cast<BranchInst>(EntryTI)->isUnconditional() ||
110 EntryTI->getSuccessor(0) != L->getHeader()) {
111 ShouldExtractLoop = true;
112 } else {
113 // Check to see if any exits from the loop are more than just return
114 // blocks.
115 SmallVector<BasicBlock*, 8> ExitBlocks;
116 L->getExitBlocks(ExitBlocks);
117 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
118 if (!isa<ReturnInst>(ExitBlocks[i]->getTerminator())) {
119 ShouldExtractLoop = true;
120 break;
121 }
122 }
123
124 if (ShouldExtractLoop) {
125 // We must omit EH pads. EH pads must accompany the invoke
126 // instruction. But this would result in a loop in the extracted
127 // function. An infinite cycle occurs when it tries to extract that loop as
128 // well.
129 SmallVector<BasicBlock*, 8> ExitBlocks;
130 L->getExitBlocks(ExitBlocks);
131 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
132 if (ExitBlocks[i]->isEHPad()) {
133 ShouldExtractLoop = false;
134 break;
135 }
136 }
137
138 if (ShouldExtractLoop) {
139 if (NumLoops == 0) return Changed;
140 --NumLoops;
141 CodeExtractor Extractor(DT, *L);
142 if (Extractor.extractCodeRegion() != nullptr) {
143 Changed = true;
144 // After extraction, the loop is replaced by a function call, so
145 // we shouldn't try to run any more loop passes on it.
146 LI.updateUnloop(L);
147 }
148 ++NumExtracted;
149 }
150
151 return Changed;
152 }
153
154 // createSingleLoopExtractorPass - This pass extracts one natural loop from the
155 // program into a function if it can. This is used by bugpoint.
156 //
createSingleLoopExtractorPass()157 Pass *llvm::createSingleLoopExtractorPass() {
158 return new SingleLoopExtractor();
159 }
160
161
162 // BlockFile - A file which contains a list of blocks that should not be
163 // extracted.
164 static cl::opt<std::string>
165 BlockFile("extract-blocks-file", cl::value_desc("filename"),
166 cl::desc("A file containing list of basic blocks to not extract"),
167 cl::Hidden);
168
169 namespace {
170 /// BlockExtractorPass - This pass is used by bugpoint to extract all blocks
171 /// from the module into their own functions except for those specified by the
172 /// BlocksToNotExtract list.
173 class BlockExtractorPass : public ModulePass {
174 void LoadFile(const char *Filename);
175 void SplitLandingPadPreds(Function *F);
176
177 std::vector<BasicBlock*> BlocksToNotExtract;
178 std::vector<std::pair<std::string, std::string> > BlocksToNotExtractByName;
179 public:
180 static char ID; // Pass identification, replacement for typeid
BlockExtractorPass()181 BlockExtractorPass() : ModulePass(ID) {
182 if (!BlockFile.empty())
183 LoadFile(BlockFile.c_str());
184 }
185
186 bool runOnModule(Module &M) override;
187 };
188 }
189
190 char BlockExtractorPass::ID = 0;
191 INITIALIZE_PASS(BlockExtractorPass, "extract-blocks",
192 "Extract Basic Blocks From Module (for bugpoint use)",
193 false, false)
194
195 // createBlockExtractorPass - This pass extracts all blocks (except those
196 // specified in the argument list) from the functions in the module.
197 //
createBlockExtractorPass()198 ModulePass *llvm::createBlockExtractorPass() {
199 return new BlockExtractorPass();
200 }
201
LoadFile(const char * Filename)202 void BlockExtractorPass::LoadFile(const char *Filename) {
203 // Load the BlockFile...
204 std::ifstream In(Filename);
205 if (!In.good()) {
206 errs() << "WARNING: BlockExtractor couldn't load file '" << Filename
207 << "'!\n";
208 return;
209 }
210 while (In) {
211 std::string FunctionName, BlockName;
212 In >> FunctionName;
213 In >> BlockName;
214 if (!BlockName.empty())
215 BlocksToNotExtractByName.push_back(
216 std::make_pair(FunctionName, BlockName));
217 }
218 }
219
220 /// SplitLandingPadPreds - The landing pad needs to be extracted with the invoke
221 /// instruction. The critical edge breaker will refuse to break critical edges
222 /// to a landing pad. So do them here. After this method runs, all landing pads
223 /// should have only one predecessor.
SplitLandingPadPreds(Function * F)224 void BlockExtractorPass::SplitLandingPadPreds(Function *F) {
225 for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
226 InvokeInst *II = dyn_cast<InvokeInst>(I);
227 if (!II) continue;
228 BasicBlock *Parent = II->getParent();
229 BasicBlock *LPad = II->getUnwindDest();
230
231 // Look through the landing pad's predecessors. If one of them ends in an
232 // 'invoke', then we want to split the landing pad.
233 bool Split = false;
234 for (pred_iterator
235 PI = pred_begin(LPad), PE = pred_end(LPad); PI != PE; ++PI) {
236 BasicBlock *BB = *PI;
237 if (BB->isLandingPad() && BB != Parent &&
238 isa<InvokeInst>(Parent->getTerminator())) {
239 Split = true;
240 break;
241 }
242 }
243
244 if (!Split) continue;
245
246 SmallVector<BasicBlock*, 2> NewBBs;
247 SplitLandingPadPredecessors(LPad, Parent, ".1", ".2", NewBBs);
248 }
249 }
250
runOnModule(Module & M)251 bool BlockExtractorPass::runOnModule(Module &M) {
252 std::set<BasicBlock*> TranslatedBlocksToNotExtract;
253 for (unsigned i = 0, e = BlocksToNotExtract.size(); i != e; ++i) {
254 BasicBlock *BB = BlocksToNotExtract[i];
255 Function *F = BB->getParent();
256
257 // Map the corresponding function in this module.
258 Function *MF = M.getFunction(F->getName());
259 assert(MF->getFunctionType() == F->getFunctionType() && "Wrong function?");
260
261 // Figure out which index the basic block is in its function.
262 Function::iterator BBI = MF->begin();
263 std::advance(BBI, std::distance(F->begin(), Function::iterator(BB)));
264 TranslatedBlocksToNotExtract.insert(&*BBI);
265 }
266
267 while (!BlocksToNotExtractByName.empty()) {
268 // There's no way to find BBs by name without looking at every BB inside
269 // every Function. Fortunately, this is always empty except when used by
270 // bugpoint in which case correctness is more important than performance.
271
272 std::string &FuncName = BlocksToNotExtractByName.back().first;
273 std::string &BlockName = BlocksToNotExtractByName.back().second;
274
275 for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI) {
276 Function &F = *FI;
277 if (F.getName() != FuncName) continue;
278
279 for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) {
280 BasicBlock &BB = *BI;
281 if (BB.getName() != BlockName) continue;
282
283 TranslatedBlocksToNotExtract.insert(&*BI);
284 }
285 }
286
287 BlocksToNotExtractByName.pop_back();
288 }
289
290 // Now that we know which blocks to not extract, figure out which ones we WANT
291 // to extract.
292 std::vector<BasicBlock*> BlocksToExtract;
293 for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
294 SplitLandingPadPreds(&*F);
295 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
296 if (!TranslatedBlocksToNotExtract.count(&*BB))
297 BlocksToExtract.push_back(&*BB);
298 }
299
300 for (unsigned i = 0, e = BlocksToExtract.size(); i != e; ++i) {
301 SmallVector<BasicBlock*, 2> BlocksToExtractVec;
302 BlocksToExtractVec.push_back(BlocksToExtract[i]);
303 if (const InvokeInst *II =
304 dyn_cast<InvokeInst>(BlocksToExtract[i]->getTerminator()))
305 BlocksToExtractVec.push_back(II->getUnwindDest());
306 CodeExtractor(BlocksToExtractVec).extractCodeRegion();
307 }
308
309 return !BlocksToExtract.empty();
310 }
311