1 //===- PartialInlining.cpp - Inline parts of functions --------------------===// 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 // This pass performs partial inlining, typically by inlining an if statement 11 // that surrounds the body of the function. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #include "llvm/Transforms/IPO.h" 16 #include "llvm/ADT/Statistic.h" 17 #include "llvm/IR/CFG.h" 18 #include "llvm/IR/Dominators.h" 19 #include "llvm/IR/Instructions.h" 20 #include "llvm/IR/Module.h" 21 #include "llvm/Pass.h" 22 #include "llvm/Transforms/Utils/Cloning.h" 23 #include "llvm/Transforms/Utils/CodeExtractor.h" 24 using namespace llvm; 25 26 #define DEBUG_TYPE "partialinlining" 27 28 STATISTIC(NumPartialInlined, "Number of functions partially inlined"); 29 30 namespace { 31 struct PartialInliner : public ModulePass { 32 void getAnalysisUsage(AnalysisUsage &AU) const override { } 33 static char ID; // Pass identification, replacement for typeid 34 PartialInliner() : ModulePass(ID) { 35 initializePartialInlinerPass(*PassRegistry::getPassRegistry()); 36 } 37 38 bool runOnModule(Module& M) override; 39 40 private: 41 Function* unswitchFunction(Function* F); 42 }; 43 } 44 45 char PartialInliner::ID = 0; 46 INITIALIZE_PASS(PartialInliner, "partial-inliner", 47 "Partial Inliner", false, false) 48 49 ModulePass* llvm::createPartialInliningPass() { return new PartialInliner(); } 50 51 Function* PartialInliner::unswitchFunction(Function* F) { 52 // First, verify that this function is an unswitching candidate... 53 BasicBlock* entryBlock = F->begin(); 54 BranchInst *BR = dyn_cast<BranchInst>(entryBlock->getTerminator()); 55 if (!BR || BR->isUnconditional()) 56 return nullptr; 57 58 BasicBlock* returnBlock = nullptr; 59 BasicBlock* nonReturnBlock = nullptr; 60 unsigned returnCount = 0; 61 for (succ_iterator SI = succ_begin(entryBlock), SE = succ_end(entryBlock); 62 SI != SE; ++SI) 63 if (isa<ReturnInst>((*SI)->getTerminator())) { 64 returnBlock = *SI; 65 returnCount++; 66 } else 67 nonReturnBlock = *SI; 68 69 if (returnCount != 1) 70 return nullptr; 71 72 // Clone the function, so that we can hack away on it. 73 ValueToValueMapTy VMap; 74 Function* duplicateFunction = CloneFunction(F, VMap, 75 /*ModuleLevelChanges=*/false); 76 duplicateFunction->setLinkage(GlobalValue::InternalLinkage); 77 F->getParent()->getFunctionList().push_back(duplicateFunction); 78 BasicBlock* newEntryBlock = cast<BasicBlock>(VMap[entryBlock]); 79 BasicBlock* newReturnBlock = cast<BasicBlock>(VMap[returnBlock]); 80 BasicBlock* newNonReturnBlock = cast<BasicBlock>(VMap[nonReturnBlock]); 81 82 // Go ahead and update all uses to the duplicate, so that we can just 83 // use the inliner functionality when we're done hacking. 84 F->replaceAllUsesWith(duplicateFunction); 85 86 // Special hackery is needed with PHI nodes that have inputs from more than 87 // one extracted block. For simplicity, just split the PHIs into a two-level 88 // sequence of PHIs, some of which will go in the extracted region, and some 89 // of which will go outside. 90 BasicBlock* preReturn = newReturnBlock; 91 newReturnBlock = newReturnBlock->splitBasicBlock( 92 newReturnBlock->getFirstNonPHI()); 93 BasicBlock::iterator I = preReturn->begin(); 94 BasicBlock::iterator Ins = newReturnBlock->begin(); 95 while (I != preReturn->end()) { 96 PHINode* OldPhi = dyn_cast<PHINode>(I); 97 if (!OldPhi) break; 98 99 PHINode* retPhi = PHINode::Create(OldPhi->getType(), 2, "", Ins); 100 OldPhi->replaceAllUsesWith(retPhi); 101 Ins = newReturnBlock->getFirstNonPHI(); 102 103 retPhi->addIncoming(I, preReturn); 104 retPhi->addIncoming(OldPhi->getIncomingValueForBlock(newEntryBlock), 105 newEntryBlock); 106 OldPhi->removeIncomingValue(newEntryBlock); 107 108 ++I; 109 } 110 newEntryBlock->getTerminator()->replaceUsesOfWith(preReturn, newReturnBlock); 111 112 // Gather up the blocks that we're going to extract. 113 std::vector<BasicBlock*> toExtract; 114 toExtract.push_back(newNonReturnBlock); 115 for (Function::iterator FI = duplicateFunction->begin(), 116 FE = duplicateFunction->end(); FI != FE; ++FI) 117 if (&*FI != newEntryBlock && &*FI != newReturnBlock && 118 &*FI != newNonReturnBlock) 119 toExtract.push_back(FI); 120 121 // The CodeExtractor needs a dominator tree. 122 DominatorTree DT; 123 DT.recalculate(*duplicateFunction); 124 125 // Extract the body of the if. 126 Function* extractedFunction 127 = CodeExtractor(toExtract, &DT).extractCodeRegion(); 128 129 InlineFunctionInfo IFI; 130 131 // Inline the top-level if test into all callers. 132 std::vector<User *> Users(duplicateFunction->user_begin(), 133 duplicateFunction->user_end()); 134 for (std::vector<User*>::iterator UI = Users.begin(), UE = Users.end(); 135 UI != UE; ++UI) 136 if (CallInst *CI = dyn_cast<CallInst>(*UI)) 137 InlineFunction(CI, IFI); 138 else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) 139 InlineFunction(II, IFI); 140 141 // Ditch the duplicate, since we're done with it, and rewrite all remaining 142 // users (function pointers, etc.) back to the original function. 143 duplicateFunction->replaceAllUsesWith(F); 144 duplicateFunction->eraseFromParent(); 145 146 ++NumPartialInlined; 147 148 return extractedFunction; 149 } 150 151 bool PartialInliner::runOnModule(Module& M) { 152 std::vector<Function*> worklist; 153 worklist.reserve(M.size()); 154 for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI) 155 if (!FI->use_empty() && !FI->isDeclaration()) 156 worklist.push_back(&*FI); 157 158 bool changed = false; 159 while (!worklist.empty()) { 160 Function* currFunc = worklist.back(); 161 worklist.pop_back(); 162 163 if (currFunc->use_empty()) continue; 164 165 bool recursive = false; 166 for (User *U : currFunc->users()) 167 if (Instruction* I = dyn_cast<Instruction>(U)) 168 if (I->getParent()->getParent() == currFunc) { 169 recursive = true; 170 break; 171 } 172 if (recursive) continue; 173 174 175 if (Function* newFunc = unswitchFunction(currFunc)) { 176 worklist.push_back(newFunc); 177 changed = true; 178 } 179 180 } 181 182 return changed; 183 } 184