//===- PartialInlining.cpp - Inline parts of functions --------------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This pass performs partial inlining, typically by inlining an if statement // that surrounds the body of the function. // //===----------------------------------------------------------------------===// #include "llvm/Transforms/IPO.h" #include "llvm/ADT/Statistic.h" #include "llvm/IR/CFG.h" #include "llvm/IR/Dominators.h" #include "llvm/IR/Instructions.h" #include "llvm/IR/Module.h" #include "llvm/Pass.h" #include "llvm/Transforms/Utils/Cloning.h" #include "llvm/Transforms/Utils/CodeExtractor.h" using namespace llvm; #define DEBUG_TYPE "partialinlining" STATISTIC(NumPartialInlined, "Number of functions partially inlined"); namespace { struct PartialInliner : public ModulePass { void getAnalysisUsage(AnalysisUsage &AU) const override { } static char ID; // Pass identification, replacement for typeid PartialInliner() : ModulePass(ID) { initializePartialInlinerPass(*PassRegistry::getPassRegistry()); } bool runOnModule(Module& M) override; private: Function* unswitchFunction(Function* F); }; } char PartialInliner::ID = 0; INITIALIZE_PASS(PartialInliner, "partial-inliner", "Partial Inliner", false, false) ModulePass* llvm::createPartialInliningPass() { return new PartialInliner(); } Function* PartialInliner::unswitchFunction(Function* F) { // First, verify that this function is an unswitching candidate... BasicBlock* entryBlock = F->begin(); BranchInst *BR = dyn_cast<BranchInst>(entryBlock->getTerminator()); if (!BR || BR->isUnconditional()) return nullptr; BasicBlock* returnBlock = nullptr; BasicBlock* nonReturnBlock = nullptr; unsigned returnCount = 0; for (succ_iterator SI = succ_begin(entryBlock), SE = succ_end(entryBlock); SI != SE; ++SI) if (isa<ReturnInst>((*SI)->getTerminator())) { returnBlock = *SI; returnCount++; } else nonReturnBlock = *SI; if (returnCount != 1) return nullptr; // Clone the function, so that we can hack away on it. ValueToValueMapTy VMap; Function* duplicateFunction = CloneFunction(F, VMap, /*ModuleLevelChanges=*/false); duplicateFunction->setLinkage(GlobalValue::InternalLinkage); F->getParent()->getFunctionList().push_back(duplicateFunction); BasicBlock* newEntryBlock = cast<BasicBlock>(VMap[entryBlock]); BasicBlock* newReturnBlock = cast<BasicBlock>(VMap[returnBlock]); BasicBlock* newNonReturnBlock = cast<BasicBlock>(VMap[nonReturnBlock]); // Go ahead and update all uses to the duplicate, so that we can just // use the inliner functionality when we're done hacking. F->replaceAllUsesWith(duplicateFunction); // Special hackery is needed with PHI nodes that have inputs from more than // one extracted block. For simplicity, just split the PHIs into a two-level // sequence of PHIs, some of which will go in the extracted region, and some // of which will go outside. BasicBlock* preReturn = newReturnBlock; newReturnBlock = newReturnBlock->splitBasicBlock( newReturnBlock->getFirstNonPHI()); BasicBlock::iterator I = preReturn->begin(); BasicBlock::iterator Ins = newReturnBlock->begin(); while (I != preReturn->end()) { PHINode* OldPhi = dyn_cast<PHINode>(I); if (!OldPhi) break; PHINode* retPhi = PHINode::Create(OldPhi->getType(), 2, "", Ins); OldPhi->replaceAllUsesWith(retPhi); Ins = newReturnBlock->getFirstNonPHI(); retPhi->addIncoming(I, preReturn); retPhi->addIncoming(OldPhi->getIncomingValueForBlock(newEntryBlock), newEntryBlock); OldPhi->removeIncomingValue(newEntryBlock); ++I; } newEntryBlock->getTerminator()->replaceUsesOfWith(preReturn, newReturnBlock); // Gather up the blocks that we're going to extract. std::vector<BasicBlock*> toExtract; toExtract.push_back(newNonReturnBlock); for (Function::iterator FI = duplicateFunction->begin(), FE = duplicateFunction->end(); FI != FE; ++FI) if (&*FI != newEntryBlock && &*FI != newReturnBlock && &*FI != newNonReturnBlock) toExtract.push_back(FI); // The CodeExtractor needs a dominator tree. DominatorTree DT; DT.recalculate(*duplicateFunction); // Extract the body of the if. Function* extractedFunction = CodeExtractor(toExtract, &DT).extractCodeRegion(); InlineFunctionInfo IFI; // Inline the top-level if test into all callers. std::vector<User *> Users(duplicateFunction->user_begin(), duplicateFunction->user_end()); for (std::vector<User*>::iterator UI = Users.begin(), UE = Users.end(); UI != UE; ++UI) if (CallInst *CI = dyn_cast<CallInst>(*UI)) InlineFunction(CI, IFI); else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) InlineFunction(II, IFI); // Ditch the duplicate, since we're done with it, and rewrite all remaining // users (function pointers, etc.) back to the original function. duplicateFunction->replaceAllUsesWith(F); duplicateFunction->eraseFromParent(); ++NumPartialInlined; return extractedFunction; } bool PartialInliner::runOnModule(Module& M) { std::vector<Function*> worklist; worklist.reserve(M.size()); for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI) if (!FI->use_empty() && !FI->isDeclaration()) worklist.push_back(&*FI); bool changed = false; while (!worklist.empty()) { Function* currFunc = worklist.back(); worklist.pop_back(); if (currFunc->use_empty()) continue; bool recursive = false; for (User *U : currFunc->users()) if (Instruction* I = dyn_cast<Instruction>(U)) if (I->getParent()->getParent() == currFunc) { recursive = true; break; } if (recursive) continue; if (Function* newFunc = unswitchFunction(currFunc)) { worklist.push_back(newFunc); changed = true; } } return changed; }