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/Pass.h"
  23 #include "llvm/ADT/Statistic.h"
  24 #include "llvm/Target/TargetData.h"
  25 #include "llvm/Support/Compiler.h"
  26 using namespace llvm;
  27
  28 STATISTIC(NumLowered, "Number of allocations lowered");
  29
  30 namespace {
  31   /// LowerAllocations - Turn malloc and free instructions into %malloc and
  32   /// %free calls.
  33   ///
  34   class VISIBILITY_HIDDEN LowerAllocations : public BasicBlockPass {
  35     Constant *MallocFunc;   // Functions in the module we are processing
  36     Constant *FreeFunc;     // Initialized by doInitialization
  37     bool LowerMallocArgToInteger;
  38   public:
  39     static char ID; // Pass ID, replacement for typeid
  40     explicit LowerAllocations(bool LowerToInt = false)
  41       : BasicBlockPass(&ID), MallocFunc(0), FreeFunc(0),
  42         LowerMallocArgToInteger(LowerToInt) {}
  43
  44     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  45       AU.addRequired<TargetData>();
  46       AU.setPreservesCFG();
  47
  48       // This is a cluster of orthogonal Transforms:
  49       AU.addPreserved<UnifyFunctionExitNodes>();
  50       AU.addPreservedID(PromoteMemoryToRegisterID);
  51       AU.addPreservedID(LowerSwitchID);
  52       AU.addPreservedID(LowerInvokePassID);
  53     }
  54
  55     /// doPassInitialization - For the lower allocations pass, this ensures that
  56     /// a module contains a declaration for a malloc and a free function.
  57     ///
  58     bool doInitialization(Module &M);
  59
  60     virtual bool doInitialization(Function &F) {
  61       return doInitialization(*F.getParent());
  62     }
  63
  64     /// runOnBasicBlock - This method does the actual work of converting
  65     /// instructions over, assuming that the pass has already been initialized.
  66     ///
  67     bool runOnBasicBlock(BasicBlock &BB);
  68   };
  69 }
  70
  71 char LowerAllocations::ID = 0;
  72 static RegisterPass<LowerAllocations>
  73 X("lowerallocs", "Lower allocations from instructions to calls");
  74
  75 // Publically exposed interface to pass...
  76 const PassInfo *const llvm::LowerAllocationsID = &X;
  77 // createLowerAllocationsPass - Interface to this file...
  78 Pass *llvm::createLowerAllocationsPass(bool LowerMallocArgToInteger) {
  79   return new LowerAllocations(LowerMallocArgToInteger);
  80 }
  81
  82
  83 // doInitialization - For the lower allocations pass, this ensures that a
  84 // module contains a declaration for a malloc and a free function.
  85 //
  86 // This function is always successful.
  87 //
  88 bool LowerAllocations::doInitialization(Module &M) {
  89   const Type *BPTy = PointerType::getUnqual(Type::Int8Ty);
  90   // Prototype malloc as "char* malloc(...)", because we don't know in
  91   // doInitialization whether size_t is int or long.
  92   FunctionType *FT = FunctionType::get(BPTy, std::vector<const Type*>(), true);
  93   MallocFunc = M.getOrInsertFunction("malloc", FT);
  94   FreeFunc = M.getOrInsertFunction("free"  , Type::VoidTy, BPTy, (Type *)0);
  95   return true;
  96 }
  97
  98 // runOnBasicBlock - This method does the actual work of converting
  99 // instructions over, assuming that the pass has already been initialized.
 100 //
 101 bool LowerAllocations::runOnBasicBlock(BasicBlock &BB) {
 102   bool Changed = false;
 103   assert(MallocFunc && FreeFunc && "Pass not initialized!");
 104
 105   BasicBlock::InstListType &BBIL = BB.getInstList();
 106
 107   const TargetData &TD = getAnalysis<TargetData>();
 108   const Type *IntPtrTy = TD.getIntPtrType();
 109
 110   // Loop over all of the instructions, looking for malloc or free instructions
 111   for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) {
 112     if (MallocInst *MI = dyn_cast<MallocInst>(I)) {
 113       const Type *AllocTy = MI->getType()->getElementType();
 114
 115       // malloc(type) becomes sbyte *malloc(size)
 116       Value *MallocArg;
 117       if (LowerMallocArgToInteger)
 118         MallocArg = ConstantInt::get(Type::Int64Ty,
 119                                      TD.getTypePaddedSize(AllocTy));
 120       else
 121         MallocArg = ConstantExpr::getSizeOf(AllocTy);
 122       MallocArg = ConstantExpr::getTruncOrBitCast(cast<Constant>(MallocArg),
 123                                                   IntPtrTy);
 124
 125       if (MI->isArrayAllocation()) {
 126         if (isa<ConstantInt>(MallocArg) &&
 127             cast<ConstantInt>(MallocArg)->isOne()) {
 128           MallocArg = MI->getOperand(0);         // Operand * 1 = Operand
 129         } else if (Constant *CO = dyn_cast<Constant>(MI->getOperand(0))) {
 130           CO = ConstantExpr::getIntegerCast(CO, IntPtrTy, false /*ZExt*/);
 131           MallocArg = ConstantExpr::getMul(CO, cast<Constant>(MallocArg));
 132         } else {
 133           Value *Scale = MI->getOperand(0);
 134           if (Scale->getType() != IntPtrTy)
 135             Scale = CastInst::CreateIntegerCast(Scale, IntPtrTy, false /*ZExt*/,
 136                                                 "", I);
 137
 138           // Multiply it by the array size if necessary...
 139           MallocArg = BinaryOperator::Create(Instruction::Mul, Scale,
 140                                              MallocArg, "", I);
 141         }
 142       }
 143
 144       // Create the call to Malloc.
 145       CallInst *MCall = CallInst::Create(MallocFunc, MallocArg, "", I);
 146       MCall->setTailCall();
 147
 148       // Create a cast instruction to convert to the right type...
 149       Value *MCast;
 150       if (MCall->getType() != Type::VoidTy)
 151         MCast = new BitCastInst(MCall, MI->getType(), "", I);
 152       else
 153         MCast = Constant::getNullValue(MI->getType());
 154
 155       // Replace all uses of the old malloc inst with the cast inst
 156       MI->replaceAllUsesWith(MCast);
 157       I = --BBIL.erase(I);         // remove and delete the malloc instr...
 158       Changed = true;
 159       ++NumLowered;
 160     } else if (FreeInst *FI = dyn_cast<FreeInst>(I)) {
 161       Value *PtrCast =
 162         new BitCastInst(FI->getOperand(0),
 163                         PointerType::getUnqual(Type::Int8Ty), "", I);
 164
 165       // Insert a call to the free function...
 166       CallInst::Create(FreeFunc, PtrCast, "", I)->setTailCall();
 167
 168       // Delete the old free instruction
 169       I = --BBIL.erase(I);
 170       Changed = true;
 171       ++NumLowered;
 172     }
 173   }
 174
 175   return Changed;
 176 }
 177