1 //===- Reg2Mem.cpp - Convert registers to allocas -------------------------===// 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 demotes all registers to memory references. It is intended to be 11 // the inverse of PromoteMemoryToRegister. By converting to loads, the only 12 // values live across basic blocks are allocas and loads before phi nodes. 13 // It is intended that this should make CFG hacking much easier. 14 // To make later hacking easier, the entry block is split into two, such that 15 // all introduced allocas and nothing else are in the entry block. 16 // 17 //===----------------------------------------------------------------------===// 18 19 #define DEBUG_TYPE "reg2mem" 20 #include "llvm/Transforms/Scalar.h" 21 #include "llvm/ADT/Statistic.h" 22 #include "llvm/IR/BasicBlock.h" 23 #include "llvm/IR/Function.h" 24 #include "llvm/IR/Instructions.h" 25 #include "llvm/IR/LLVMContext.h" 26 #include "llvm/IR/Module.h" 27 #include "llvm/Pass.h" 28 #include "llvm/Support/CFG.h" 29 #include "llvm/Transforms/Utils/Local.h" 30 #include <list> 31 using namespace llvm; 32 33 STATISTIC(NumRegsDemoted, "Number of registers demoted"); 34 STATISTIC(NumPhisDemoted, "Number of phi-nodes demoted"); 35 36 namespace { 37 struct RegToMem : public FunctionPass { 38 static char ID; // Pass identification, replacement for typeid 39 RegToMem() : FunctionPass(ID) { 40 initializeRegToMemPass(*PassRegistry::getPassRegistry()); 41 } 42 43 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 44 AU.addRequiredID(BreakCriticalEdgesID); 45 AU.addPreservedID(BreakCriticalEdgesID); 46 } 47 48 bool valueEscapes(const Instruction *Inst) const { 49 const BasicBlock *BB = Inst->getParent(); 50 for (Value::const_use_iterator UI = Inst->use_begin(),E = Inst->use_end(); 51 UI != E; ++UI) { 52 const Instruction *I = cast<Instruction>(*UI); 53 if (I->getParent() != BB || isa<PHINode>(I)) 54 return true; 55 } 56 return false; 57 } 58 59 virtual bool runOnFunction(Function &F); 60 }; 61 } 62 63 char RegToMem::ID = 0; 64 INITIALIZE_PASS_BEGIN(RegToMem, "reg2mem", "Demote all values to stack slots", 65 false, false) 66 INITIALIZE_PASS_DEPENDENCY(BreakCriticalEdges) 67 INITIALIZE_PASS_END(RegToMem, "reg2mem", "Demote all values to stack slots", 68 false, false) 69 70 bool RegToMem::runOnFunction(Function &F) { 71 if (F.isDeclaration()) 72 return false; 73 74 // Insert all new allocas into entry block. 75 BasicBlock *BBEntry = &F.getEntryBlock(); 76 assert(pred_begin(BBEntry) == pred_end(BBEntry) && 77 "Entry block to function must not have predecessors!"); 78 79 // Find first non-alloca instruction and create insertion point. This is 80 // safe if block is well-formed: it always have terminator, otherwise 81 // we'll get and assertion. 82 BasicBlock::iterator I = BBEntry->begin(); 83 while (isa<AllocaInst>(I)) ++I; 84 85 CastInst *AllocaInsertionPoint = 86 new BitCastInst(Constant::getNullValue(Type::getInt32Ty(F.getContext())), 87 Type::getInt32Ty(F.getContext()), 88 "reg2mem alloca point", I); 89 90 // Find the escaped instructions. But don't create stack slots for 91 // allocas in entry block. 92 std::list<Instruction*> WorkList; 93 for (Function::iterator ibb = F.begin(), ibe = F.end(); 94 ibb != ibe; ++ibb) 95 for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end(); 96 iib != iie; ++iib) { 97 if (!(isa<AllocaInst>(iib) && iib->getParent() == BBEntry) && 98 valueEscapes(iib)) { 99 WorkList.push_front(&*iib); 100 } 101 } 102 103 // Demote escaped instructions 104 NumRegsDemoted += WorkList.size(); 105 for (std::list<Instruction*>::iterator ilb = WorkList.begin(), 106 ile = WorkList.end(); ilb != ile; ++ilb) 107 DemoteRegToStack(**ilb, false, AllocaInsertionPoint); 108 109 WorkList.clear(); 110 111 // Find all phi's 112 for (Function::iterator ibb = F.begin(), ibe = F.end(); 113 ibb != ibe; ++ibb) 114 for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end(); 115 iib != iie; ++iib) 116 if (isa<PHINode>(iib)) 117 WorkList.push_front(&*iib); 118 119 // Demote phi nodes 120 NumPhisDemoted += WorkList.size(); 121 for (std::list<Instruction*>::iterator ilb = WorkList.begin(), 122 ile = WorkList.end(); ilb != ile; ++ilb) 123 DemotePHIToStack(cast<PHINode>(*ilb), AllocaInsertionPoint); 124 125 return true; 126 } 127 128 129 // createDemoteRegisterToMemory - Provide an entry point to create this pass. 130 char &llvm::DemoteRegisterToMemoryID = RegToMem::ID; 131 FunctionPass *llvm::createDemoteRegisterToMemoryPass() { 132 return new RegToMem(); 133 } 134