lib/Transforms/Utils/LowerAllocations.cpp

//===- LowerAllocations.cpp - Remove Malloc & Free Instructions -------------=//
//
// This file implements a pass that lowers malloc and free instructions to
// calls to %malloc & %free functions.  This transformation is a target
// dependant tranformation because we depend on the size of data types and
// alignment constraints.
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/LowerAllocations.h"
#include "llvm/Target/TargetData.h"
#include "llvm/DerivedTypes.h"
#include "llvm/iMemory.h"
#include "llvm/iOther.h"
#include "llvm/SymbolTable.h"
#include "llvm/ConstantVals.h"
using std::vector;


// doInitialization - For the lower allocations pass, this ensures that a
// module contains a declaration for a malloc and a free function.
//
// This function is always successful.
//
bool LowerAllocations::doInitialization(Module *M) {
  bool Changed = false;
  const MethodType *MallocType = 
    MethodType::get(PointerType::get(Type::SByteTy),
                    vector<const Type*>(1, Type::UIntTy), false);

  SymbolTable *SymTab = M->getSymbolTableSure();
  
  // Check for a definition of malloc
  if (Value *V = SymTab->lookup(PointerType::get(MallocType), "malloc")) {
    MallocMeth = cast<Method>(V);      // Yup, got it
  } else {                             // Nope, add one
    M->getMethodList().push_back(MallocMeth = new Method(MallocType, false, 
                                                         "malloc"));
    Changed = true;
  }

  const MethodType *FreeType = 
    MethodType::get(Type::VoidTy,
                    vector<const Type*>(1, PointerType::get(Type::SByteTy)),
		    false);

  // Check for a definition of free
  if (Value *V = SymTab->lookup(PointerType::get(FreeType), "free")) {
    FreeMeth = cast<Method>(V);      // Yup, got it
  } else {                             // Nope, add one
    M->getMethodList().push_back(FreeMeth = new Method(FreeType, false,"free"));
    Changed = true;
  }

  return Changed;
}

// runOnBasicBlock - This method does the actual work of converting
// instructions over, assuming that the pass has already been initialized.
//
bool LowerAllocations::runOnBasicBlock(BasicBlock *BB) {
  bool Changed = false;
  assert(MallocMeth && FreeMeth && BB && "Pass not initialized!");

  // Loop over all of the instructions, looking for malloc or free instructions
  for (unsigned i = 0; i < BB->size(); ++i) {
    BasicBlock::InstListType &BBIL = BB->getInstList();
    if (MallocInst *MI = dyn_cast<MallocInst>(*(BBIL.begin()+i))) {
      BBIL.remove(BBIL.begin()+i);   // remove the malloc instr...
        
      const Type *AllocTy =cast<PointerType>(MI->getType())->getElementType();
      
      // Get the number of bytes to be allocated for one element of the
      // requested type...
      unsigned Size = DataLayout.getTypeSize(AllocTy);
      
      // malloc(type) becomes sbyte *malloc(constint)
      Value *MallocArg = ConstantUInt::get(Type::UIntTy, Size);
      if (MI->getNumOperands() && Size == 1) {
        MallocArg = MI->getOperand(0);         // Operand * 1 = Operand
      } else if (MI->getNumOperands()) {
        // Multiply it by the array size if neccesary...
        MallocArg = BinaryOperator::create(Instruction::Mul,MI->getOperand(0),
                                           MallocArg);
        BBIL.insert(BBIL.begin()+i++, cast<Instruction>(MallocArg));
      }
      
      // Create the call to Malloc...
      CallInst *MCall = new CallInst(MallocMeth,
                                     vector<Value*>(1, MallocArg));
      BBIL.insert(BBIL.begin()+i, MCall);
      
      // Create a cast instruction to convert to the right type...
      CastInst *MCast = new CastInst(MCall, MI->getType());
      BBIL.insert(BBIL.begin()+i+1, MCast);
      
      // Replace all uses of the old malloc inst with the cast inst
      MI->replaceAllUsesWith(MCast);
      delete MI;                          // Delete the malloc inst
      Changed = true;
    } else if (FreeInst *FI = dyn_cast<FreeInst>(*(BBIL.begin()+i))) {
      BBIL.remove(BB->getInstList().begin()+i);
      
      // Cast the argument to free into a ubyte*...
      CastInst *MCast = new CastInst(FI->getOperand(0), 
                                     PointerType::get(Type::UByteTy));
      BBIL.insert(BBIL.begin()+i, MCast);
      
      // Insert a call to the free function...
      CallInst *FCall = new CallInst(FreeMeth,
                                     vector<Value*>(1, MCast));
      BBIL.insert(BBIL.begin()+i+1, FCall);
      
      // Delete the old free instruction
      delete FI;
      Changed = true;
    }
  }

  return Changed;
}