//===- FlattenCFGPass.cpp - CFG Flatten Pass ----------------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file implements flattening of CFG. // //===----------------------------------------------------------------------===// #include "llvm/Transforms/Scalar.h" #include "llvm/Analysis/AliasAnalysis.h" #include "llvm/IR/CFG.h" #include "llvm/Pass.h" #include "llvm/Transforms/Utils/Local.h" using namespace llvm; #define DEBUG_TYPE "flattencfg" namespace { struct FlattenCFGPass : public FunctionPass { static char ID; // Pass identification, replacement for typeid public: FlattenCFGPass() : FunctionPass(ID) { initializeFlattenCFGPassPass(*PassRegistry::getPassRegistry()); } bool runOnFunction(Function &F) override; void getAnalysisUsage(AnalysisUsage &AU) const override { AU.addRequired<AliasAnalysis>(); } private: AliasAnalysis *AA; }; } char FlattenCFGPass::ID = 0; INITIALIZE_PASS_BEGIN(FlattenCFGPass, "flattencfg", "Flatten the CFG", false, false) INITIALIZE_AG_DEPENDENCY(AliasAnalysis) INITIALIZE_PASS_END(FlattenCFGPass, "flattencfg", "Flatten the CFG", false, false) // Public interface to the FlattenCFG pass FunctionPass *llvm::createFlattenCFGPass() { return new FlattenCFGPass(); } /// iterativelyFlattenCFG - Call FlattenCFG on all the blocks in the function, /// iterating until no more changes are made. static bool iterativelyFlattenCFG(Function &F, AliasAnalysis *AA) { bool Changed = false; bool LocalChange = true; while (LocalChange) { LocalChange = false; // Loop over all of the basic blocks and remove them if they are unneeded... // for (Function::iterator BBIt = F.begin(); BBIt != F.end();) { if (FlattenCFG(BBIt++, AA)) { LocalChange = true; } } Changed |= LocalChange; } return Changed; } bool FlattenCFGPass::runOnFunction(Function &F) { AA = &getAnalysis<AliasAnalysis>(); bool EverChanged = false; // iterativelyFlattenCFG can make some blocks dead. while (iterativelyFlattenCFG(F, AA)) { removeUnreachableBlocks(F); EverChanged = true; } return EverChanged; }