llvm-project/llvm/lib/Transforms/Scalar/LowerAllocations.cpp

//===- ChangeAllocations.cpp - Modify %malloc & %free calls -----------------=//
//
// This file defines two passes that convert malloc and free instructions to
// calls to and from %malloc & %free function calls.  The LowerAllocations
// transformation is a target dependant tranformation because it depends 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"
#include "TransformInternals.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;
}

bool RaiseAllocations::doInitialization(Module *M) {
  SymbolTable *ST = M->getSymbolTable();
  if (!ST) return false;

  // If the module has a symbol table, they might be referring to the malloc
  // and free functions.  If this is the case, grab the method pointers that 
  // the module is using.
  //
  // Lookup %malloc and %free in the symbol table, for later use.  If they
  // don't exist, or are not external, we do not worry about converting calls
  // to that function into the appropriate instruction.
  //
  const PointerType *MallocType =   // Get the type for malloc
    PointerType::get(MethodType::get(PointerType::get(Type::SByteTy),
                                  vector<const Type*>(1, Type::UIntTy), false));
  MallocMeth = cast_or_null<Method>(ST->lookup(MallocType, "malloc"));
  if (MallocMeth && !MallocMeth->isExternal())
    MallocMeth = 0;  // Don't mess with locally defined versions of the fn

  const PointerType *FreeType =     // Get the type for free
    PointerType::get(MethodType::get(Type::VoidTy,
            vector<const Type*>(1, PointerType::get(Type::SByteTy)), false));
  FreeMeth = cast_or_null<Method>(ST->lookup(FreeType, "free"));
  if (FreeMeth && !FreeMeth->isExternal())
    FreeMeth = 0;  // Don't mess with locally defined versions of the fn

  return false;
}

// doOneCleanupPass - Do one pass over the input method, fixing stuff up.
//
bool RaiseAllocations::runOnBasicBlock(BasicBlock *BB) {
  bool Changed = false;
  BasicBlock::InstListType &BIL = BB->getInstList();

  for (BasicBlock::iterator BI = BB->begin(); BI != BB->end();) {
    Instruction *I = *BI;

    if (CallInst *CI = dyn_cast<CallInst>(I)) {
      if (CI->getCalledValue() == MallocMeth) {      // Replace call to malloc?
        const Type *PtrSByte = PointerType::get(Type::SByteTy);
        MallocInst *MallocI = new MallocInst(PtrSByte, CI->getOperand(1),
                                             CI->getName());
        CI->setName("");
        BI = BIL.insert(BI, MallocI)+1;
        ReplaceInstWithInst(BIL, BI, new CastInst(MallocI, PtrSByte));
        Changed = true;
        continue;  // Skip the ++BI
      } else if (CI->getCalledValue() == FreeMeth) { // Replace call to free?
        ReplaceInstWithInst(BIL, BI, new FreeInst(CI->getOperand(1)));
        Changed = true;
        continue;  // Skip the ++BI
      }
    }

    ++BI;
  }

  return Changed;
}