lib/Transforms/Utils/LowerAllocations.cpp

   1 //===- LowerAllocations.cpp - Reduce malloc & free insts to calls ---------===//
   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 // The LowerAllocations transformation is a target-dependent tranformation
  11 // because it depends on the size of data types and alignment constraints.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #define DEBUG_TYPE "lowerallocs"
  16 #include "llvm/Transforms/Scalar.h"
  17 #include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
  18 #include "llvm/Module.h"
  19 #include "llvm/DerivedTypes.h"
  20 #include "llvm/Instructions.h"
  21 #include "llvm/Constants.h"
  22 #include "llvm/LLVMContext.h"
  23 #include "llvm/Pass.h"
  24 #include "llvm/ADT/Statistic.h"
  25 #include "llvm/Target/TargetData.h"
  26 #include "llvm/Support/Compiler.h"
  27 using namespace llvm;
  28
  29 STATISTIC(NumLowered, "Number of allocations lowered");
  30
  31 namespace {
  32   /// LowerAllocations - Turn malloc and free instructions into @malloc and
  33   /// @free calls.
  34   ///
  35   class VISIBILITY_HIDDEN LowerAllocations : public BasicBlockPass {
  36     Constant *MallocFunc;   // Functions in the module we are processing
  37     Constant *FreeFunc;     // Initialized by doInitialization
  38     bool LowerMallocArgToInteger;
  39   public:
  40     static char ID; // Pass ID, replacement for typeid
  41     explicit LowerAllocations(bool LowerToInt = false)
  42       : BasicBlockPass(&ID), MallocFunc(0), FreeFunc(0),
  43         LowerMallocArgToInteger(LowerToInt) {}
  44
  45     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  46       AU.addRequired<TargetData>();
  47       AU.setPreservesCFG();
  48
  49       // This is a cluster of orthogonal Transforms:
  50       AU.addPreserved<UnifyFunctionExitNodes>();
  51       AU.addPreservedID(PromoteMemoryToRegisterID);
  52       AU.addPreservedID(LowerSwitchID);
  53       AU.addPreservedID(LowerInvokePassID);
  54     }
  55
  56     /// doPassInitialization - For the lower allocations pass, this ensures that
  57     /// a module contains a declaration for a malloc and a free function.
  58     ///
  59     bool doInitialization(Module &M);
  60
  61     virtual bool doInitialization(Function &F) {
  62       return doInitialization(*F.getParent());
  63     }
  64
  65     /// runOnBasicBlock - This method does the actual work of converting
  66     /// instructions over, assuming that the pass has already been initialized.
  67     ///
  68     bool runOnBasicBlock(BasicBlock &BB);
  69   };
  70 }
  71
  72 char LowerAllocations::ID = 0;
  73 static RegisterPass<LowerAllocations>
  74 X("lowerallocs", "Lower allocations from instructions to calls");
  75
  76 // Publically exposed interface to pass...
  77 const PassInfo *const llvm::LowerAllocationsID = &X;
  78 // createLowerAllocationsPass - Interface to this file...
  79 Pass *llvm::createLowerAllocationsPass(bool LowerMallocArgToInteger) {
  80   return new LowerAllocations(LowerMallocArgToInteger);
  81 }
  82
  83
  84 // doInitialization - For the lower allocations pass, this ensures that a
  85 // module contains a declaration for a malloc and a free function.
  86 //
  87 // This function is always successful.
  88 //
  89 bool LowerAllocations::doInitialization(Module &M) {
  90   const Type *BPTy = PointerType::getUnqual(Type::getInt8Ty(M.getContext()));
  91   // Prototype malloc as "char* malloc(...)", because we don't know in
  92   // doInitialization whether size_t is int or long.
  93   FunctionType *FT = FunctionType::get(BPTy, true);
  94   MallocFunc = M.getOrInsertFunction("malloc", FT);
  95   FreeFunc = M.getOrInsertFunction("free"  , Type::getVoidTy(M.getContext()),
  96                                    BPTy, (Type *)0);
  97   return true;
  98 }
  99
 100 // runOnBasicBlock - This method does the actual work of converting
 101 // instructions over, assuming that the pass has already been initialized.
 102 //
 103 bool LowerAllocations::runOnBasicBlock(BasicBlock &BB) {
 104   bool Changed = false;
 105   assert(MallocFunc && FreeFunc && "Pass not initialized!");
 106
 107   BasicBlock::InstListType &BBIL = BB.getInstList();
 108
 109   const TargetData &TD = getAnalysis<TargetData>();
 110   const Type *IntPtrTy = TD.getIntPtrType(BB.getContext());
 111
 112   // Loop over all of the instructions, looking for malloc or free instructions
 113   for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) {
 114     if (MallocInst *MI = dyn_cast<MallocInst>(I)) {
 115       const Type *AllocTy = MI->getType()->getElementType();
 116
 117       // malloc(type) becomes i8 *malloc(size)
 118       Value *MallocArg;
 119       if (LowerMallocArgToInteger)
 120         MallocArg = ConstantInt::get(Type::getInt64Ty(BB.getContext()),
 121                                      TD.getTypeAllocSize(AllocTy));
 122       else
 123         MallocArg = ConstantExpr::getSizeOf(AllocTy);
 124       MallocArg =
 125            ConstantExpr::getTruncOrBitCast(cast<Constant>(MallocArg),
 126                                                   IntPtrTy);
 127
 128       if (MI->isArrayAllocation()) {
 129         if (isa<ConstantInt>(MallocArg) &&
 130             cast<ConstantInt>(MallocArg)->isOne()) {
 131           MallocArg = MI->getOperand(0);         // Operand * 1 = Operand
 132         } else if (Constant *CO = dyn_cast<Constant>(MI->getOperand(0))) {
 133           CO =
 134               ConstantExpr::getIntegerCast(CO, IntPtrTy, false /*ZExt*/);
 135           MallocArg = ConstantExpr::getMul(CO,
 136                                                   cast<Constant>(MallocArg));
 137         } else {
 138           Value *Scale = MI->getOperand(0);
 139           if (Scale->getType() != IntPtrTy)
 140             Scale = CastInst::CreateIntegerCast(Scale, IntPtrTy, false /*ZExt*/,
 141                                                 "", I);
 142
 143           // Multiply it by the array size if necessary...
 144           MallocArg = BinaryOperator::Create(Instruction::Mul, Scale,
 145                                              MallocArg, "", I);
 146         }
 147       }
 148
 149       // Create the call to Malloc.
 150       CallInst *MCall = CallInst::Create(MallocFunc, MallocArg, "", I);
 151       MCall->setTailCall();
 152
 153       // Create a cast instruction to convert to the right type...
 154       Value *MCast;
 155       if (MCall->getType() != Type::getVoidTy(BB.getContext()))
 156         MCast = new BitCastInst(MCall, MI->getType(), "", I);
 157       else
 158         MCast = Constant::getNullValue(MI->getType());
 159
 160       // Replace all uses of the old malloc inst with the cast inst
 161       MI->replaceAllUsesWith(MCast);
 162       I = --BBIL.erase(I);         // remove and delete the malloc instr...
 163       Changed = true;
 164       ++NumLowered;
 165     } else if (FreeInst *FI = dyn_cast<FreeInst>(I)) {
 166       Value *PtrCast =
 167         new BitCastInst(FI->getOperand(0),
 168                PointerType::getUnqual(Type::getInt8Ty(BB.getContext())), "", I);
 169
 170       // Insert a call to the free function...
 171       CallInst::Create(FreeFunc, PtrCast, "", I)->setTailCall();
 172
 173       // Delete the old free instruction
 174       I = --BBIL.erase(I);
 175       Changed = true;
 176       ++NumLowered;
 177     }
 178   }
 179
 180   return Changed;
 181 }
 182