lib/Transforms/Utils/Linker.cpp

//===- Linker.cpp - Module Linker Implementation --------------------------===//
//
// This file implements the LLVM module linker.
//
// Specifically, this:
//  - Merges global variables between the two modules
//    - Uninit + Uninit = Init, Init + Uninit = Init, Init + Init = Error if !=
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Linker.h"
#include "llvm/Module.h"
#include "llvm/Method.h"
#include "llvm/GlobalVariable.h"
#include "llvm/SymbolTable.h"
#include "llvm/DerivedTypes.h"
#include "llvm/iOther.h"

// Error - Simple wrapper function to conditionally assign to E and return true.
// This just makes error return conditions a little bit simpler...
//
static inline bool Error(string *E, string Message) {
  if (E) *E = Message;
  return true;
}

#include "llvm/Assembly/Writer.h" // TODO: REMOVE

// RemapOperand - Use LocalMap and GlobalMap to convert references from one
// module to another.  This is somewhat sophisticated in that it can
// automatically handle constant references correctly as well...
//
static Value *RemapOperand(Value *In, map<const Value*, Value*> &LocalMap,
                           const map<const Value*, Value*> *GlobalMap = 0) {
  map<const Value*,Value*>::const_iterator I = LocalMap.find(In);
  if (I != LocalMap.end()) return I->second;

  if (GlobalMap) {
    I = GlobalMap->find(In);
    if (I != GlobalMap->end()) return I->second;
  }

  if (!isa<ConstPoolVal>(In))
    cerr << "Couldn't remap value: " << In << endl;
  return In;
}


// LinkGlobals - Loop through the global variables in the src module and merge
// them into the dest module...
//
static bool LinkGlobals(Module *Dest, const Module *Src,
                        map<const Value*, Value*> &ValueMap, string *Err = 0) {
  // We will need a module level symbol table if the src module has a module
  // level symbol table...
  SymbolTable *ST = Src->getSymbolTable() ? Dest->getSymbolTableSure() : 0;
  
  // Loop over all of the globals in the src module, mapping them over as we go
  //
  for (Module::const_giterator I = Src->gbegin(), E = Src->gend(); I != E; ++I){
    const GlobalVariable *GV = *I;
    Value *V;

    // If the global variable has a name, and that name is already in use in the
    // Dest module, make sure that the name is a compatible global variable...
    //
    if (GV->hasName() && (V = ST->lookup(GV->getType(), GV->getName()))) {
      // The same named thing is a global variable, because the only two things
      // that may be in a module level symbol table are Global Vars and Methods,
      // and they both have distinct, nonoverlapping, possible types.
      // 
      GlobalVariable *DGV = cast<GlobalVariable>(V);

      // Check to see if the two GV's have the same Const'ness...
      if (GV->isConstant() != DGV->isConstant())
        return Error(Err, "Global Variable Collision on '" + 
                     GV->getType()->getDescription() + "':%" + GV->getName() +
                     " - Global variables differ in const'ness");

      // Check to make sure that they both have the same initializer if they are
      // both initialized...
      //
 // TODO: Check to see if they have DEEP equality.  For Module level constants
      if (GV->hasInitializer() && DGV->hasInitializer() &&
          GV->getInitializer() != DGV->getInitializer())
        return Error(Err, "Global Variable Collision on '" + 
                     GV->getType()->getDescription() + "':%" + GV->getName() +
                     " - Global variables have different initializers");

      // Okay, everything is cool, remember the mapping and update the
      // initializer if neccesary...
      //
// TODO: We might have to map module level constants here!
      if (GV->hasInitializer() && !DGV->hasInitializer())
        DGV->setInitializer(GV->getInitializer());

      ValueMap.insert(make_pair(GV, DGV));
    } else {
      // No linking to be performed, simply create an identical version of the
      // symbol over in the dest module...
// TODO: Provide constpoolval mapping for initializer if using module local
// initializers!
      GlobalVariable *NGV = 
        new GlobalVariable(GV->getType()->getValueType(), GV->isConstant(),
                           GV->hasInitializer() ? GV->getInitializer() : 0,
                           GV->getName());

      // Add the new global to the dest module
      Dest->getGlobalList().push_back(NGV);

      // Make sure to remember this mapping...
      ValueMap.insert(make_pair(GV, NGV));
    }
  }
  return false;
}



// LinkMethodProtos - Link the methods together between the two modules, without
// doing method bodies... this just adds external method prototypes to the Dest
// method...
//
static bool LinkMethodProtos(Module *Dest, const Module *Src,
                             map<const Value*, Value*> &ValueMap,
                             string *Err = 0) {
  // We will need a module level symbol table if the src module has a module
  // level symbol table...
  SymbolTable *ST = Src->getSymbolTable() ? Dest->getSymbolTableSure() : 0;
  
  // Loop over all of the methods in the src module, mapping them over as we go
  //
  for (Module::const_iterator I = Src->begin(), E = Src->end(); I != E; ++I) {
    const Method *SM = *I;   // SrcMethod
    Value *V;

    // If the method has a name, and that name is already in use in the
    // Dest module, make sure that the name is a compatible method...
    //
    if (SM->hasName() && (V = ST->lookup(SM->getType(), SM->getName()))) {
      // The same named thing is a Method, because the only two things
      // that may be in a module level symbol table are Global Vars and Methods,
      // and they both have distinct, nonoverlapping, possible types.
      // 
      Method *DM = cast<Method>(V);   // DestMethod

      // Check to make sure the method is not defined in both modules...
      if (!SM->isExternal() && !DM->isExternal())
        return Error(Err, "Method '" + 
                     SM->getMethodType()->getDescription() + "':\"" + 
                     SM->getName() + "\" - Method is already defined!");

      // Otherwise, just remember this mapping...
      ValueMap.insert(make_pair(SM, DM));
    } else {
      // Method does not already exist, simply insert an external method
      // signature identical to SM into the dest module...
      Method *DM = new Method(SM->getMethodType(), SM->getName());

      // Add the method signature to the dest module...
      Dest->getMethodList().push_back(DM);

      // ... and remember this mapping...
      ValueMap.insert(make_pair(SM, DM));
    }
  }
  return false;
}

// LinkMethodBody - Copy the source method over into the dest method and fix up
// references to values.  At this point we know that Dest is an external method,
// and that Src is not.
//
static bool LinkMethodBody(Method *Dest, const Method *Src,
                           const map<const Value*, Value*> &GlobalMap,
                           string *Err = 0) {
  assert(Src && Dest && Dest->isExternal() && !Src->isExternal());
  map<const Value*, Value*> LocalMap;   // Map for method local values

  // Go through and convert method arguments over...
  for (Method::ArgumentListType::const_iterator 
         I = Src->getArgumentList().begin(),
         E = Src->getArgumentList().end(); I != E; ++I) {
    const MethodArgument *SMA = *I;

    // Create the new method argument and add to the dest method...
    MethodArgument *DMA = new MethodArgument(SMA->getType(), SMA->getName());
    Dest->getArgumentList().push_back(DMA);

    // Add a mapping to our local map
    LocalMap.insert(make_pair(SMA, DMA));
  }

  // Loop over all of the basic blocks, copying the instructions over...
  //
  for (Method::const_iterator I = Src->begin(), E = Src->end(); I != E; ++I) {
    const BasicBlock *SBB = *I;

    // Create new basic block and add to mapping and the Dest method...
    BasicBlock *DBB = new BasicBlock(SBB->getName(), Dest);
    LocalMap.insert(make_pair(SBB, DBB));

    // Loop over all of the instructions in the src basic block, copying them
    // over.  Note that this is broken in a strict sense because the cloned
    // instructions will still be referencing values in the Src module, not
    // the remapped values.  In our case, however, we will not get caught and 
    // so we can delay patching the values up until later...
    //
    for (BasicBlock::const_iterator II = SBB->begin(), IE = SBB->end(); 
         II != IE; ++II) {
      const Instruction *SI = *II;
      Instruction *DI = SI->clone();
      DBB->getInstList().push_back(DI);
      LocalMap.insert(make_pair(SI, DI));
    }
  }

  // At this point, all of the instructions and values of the method are now
  // copied over.  The only problem is that they are still referencing values
  // in the Source method as operands.  Loop through all of the operands of the
  // methods and patch them up to point to the local versions...
  //
  for (Method::inst_iterator I = Dest->inst_begin(), E = Dest->inst_end();
       I != E; ++I) {
    Instruction *Inst = *I;

    for (Instruction::op_iterator OI = Inst->op_begin(), OE = Inst->op_end();
         OI != OE; ++OI)
      *OI = RemapOperand(*OI, LocalMap, &GlobalMap);
  }

  return false;
}


// LinkMethodBodies - Link in the method bodies that are defined in the source
// module into the DestModule.  This consists basically of copying the method
// over and fixing up references to values.
//
static bool LinkMethodBodies(Module *Dest, const Module *Src,
                             map<const Value*, Value*> &ValueMap,
                             string *Err = 0) {

  // Loop over all of the methods in the src module, mapping them over as we go
  //
  for (Module::const_iterator I = Src->begin(), E = Src->end(); I != E; ++I) {
    const Method *SM = *I;                   // Source Method
    Method *DM = cast<Method>(ValueMap[SM]); // Destination method

    assert(DM && DM->isExternal() && "LinkMethodProtos failed!");
    if (!SM->isExternal())  // External methods are already done
      if (LinkMethodBody(DM, SM, ValueMap, Err)) return true;
  }
  return false;
}



// LinkModules - This function links two modules together, with the resulting
// left module modified to be the composite of the two input modules.  If an
// error occurs, true is returned and ErrorMsg (if not null) is set to indicate
// the problem.  Upon failure, the Dest module could be in a modified state, and
// shouldn't be relied on to be consistent.
//
bool LinkModules(Module *Dest, const Module *Src, string *ErrorMsg = 0) {
  // ValueMap - Mapping of values from what they used to be in Src, to what they
  // are now in Dest.
  //
  map<const Value*, Value*> ValueMap;

  // Link the globals variables together between the two modules...
  if (LinkGlobals(Dest, Src, ValueMap, ErrorMsg)) return true;

  // Link the methods together between the two modules, without doing method
  // bodies... this just adds external method prototypes to the Dest method...
  // We do this so that when we begin processing method bodies, all of the
  // global values that may be referenced are available in our ValueMap.
  //
  if (LinkMethodProtos(Dest, Src, ValueMap, ErrorMsg)) return true;

  // Link in the method bodies that are defined in the source module into the
  // DestModule.  This consists basically of copying the method over and fixing
  // up references to values.
  //
  if (LinkMethodBodies(Dest, Src, ValueMap, ErrorMsg)) return true;

  return false;
}