1//===- FlattenCFGPass.cpp - CFG Flatten Pass ----------------------===// 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 file implements flattening of CFG. 11// 12//===----------------------------------------------------------------------===// 13 14#define DEBUG_TYPE "flattencfg" 15#include "llvm/Transforms/Scalar.h" 16#include "llvm/Analysis/AliasAnalysis.h" 17#include "llvm/Pass.h" 18#include "llvm/Support/CFG.h" 19#include "llvm/Transforms/Utils/Local.h" 20using namespace llvm; 21 22namespace { 23struct FlattenCFGPass : public FunctionPass { 24 static char ID; // Pass identification, replacement for typeid 25public: 26 FlattenCFGPass() : FunctionPass(ID) { 27 initializeFlattenCFGPassPass(*PassRegistry::getPassRegistry()); 28 } 29 bool runOnFunction(Function &F); 30 31 void getAnalysisUsage(AnalysisUsage &AU) const { 32 AU.addRequired<AliasAnalysis>(); 33 } 34 35private: 36 AliasAnalysis *AA; 37}; 38} 39 40char FlattenCFGPass::ID = 0; 41INITIALIZE_PASS_BEGIN(FlattenCFGPass, "flattencfg", "Flatten the CFG", false, 42 false) 43INITIALIZE_AG_DEPENDENCY(AliasAnalysis) 44INITIALIZE_PASS_END(FlattenCFGPass, "flattencfg", "Flatten the CFG", false, 45 false) 46 47// Public interface to the FlattenCFG pass 48FunctionPass *llvm::createFlattenCFGPass() { return new FlattenCFGPass(); } 49 50/// iterativelyFlattenCFG - Call FlattenCFG on all the blocks in the function, 51/// iterating until no more changes are made. 52static bool iterativelyFlattenCFG(Function &F, AliasAnalysis *AA) { 53 bool Changed = false; 54 bool LocalChange = true; 55 while (LocalChange) { 56 LocalChange = false; 57 58 // Loop over all of the basic blocks and remove them if they are unneeded... 59 // 60 for (Function::iterator BBIt = F.begin(); BBIt != F.end();) { 61 if (FlattenCFG(BBIt++, AA)) { 62 LocalChange = true; 63 } 64 } 65 Changed |= LocalChange; 66 } 67 return Changed; 68} 69 70bool FlattenCFGPass::runOnFunction(Function &F) { 71 AA = &getAnalysis<AliasAnalysis>(); 72 bool EverChanged = false; 73 // iterativelyFlattenCFG can make some blocks dead. 74 while (iterativelyFlattenCFG(F, AA)) { 75 removeUnreachableBlocks(F); 76 EverChanged = true; 77 } 78 return EverChanged; 79} 80