//===- FunctionResolution.cpp - Resolve declarations to implementations ---===//
//
// Loop over the functions that are in the module and look for functions that
// have the same name.  More often than not, there will be things like:
//
//    declare void %foo(...)
//    void %foo(int, int) { ... }
//
// because of the way things are declared in C.  If this is the case, patch
// things up.
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/IPO.h"
#include "llvm/Module.h"
#include "llvm/SymbolTable.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Pass.h"
#include "llvm/iOther.h"
#include "llvm/Constants.h"
#include "llvm/Assembly/Writer.h"  // FIXME: remove when varargs implemented
#include "Support/Statistic.h"
#include <algorithm>

namespace {
  Statistic<>NumResolved("funcresolve", "Number of varargs functions resolved");
  Statistic<> NumGlobals("funcresolve", "Number of global variables resolved");

  struct FunctionResolvingPass : public Pass {
    bool run(Module &M);
  };
  RegisterOpt<FunctionResolvingPass> X("funcresolve", "Resolve Functions");
}

Pass *createFunctionResolvingPass() {
  return new FunctionResolvingPass();
}

// ConvertCallTo - Convert a call to a varargs function with no arg types
// specified to a concrete nonvarargs function.
//
static void ConvertCallTo(CallInst *CI, Function *Dest) {
  const FunctionType::ParamTypes &ParamTys =
    Dest->getFunctionType()->getParamTypes();
  BasicBlock *BB = CI->getParent();

  // Keep an iterator to where we want to insert cast instructions if the
  // argument types don't agree.
  //
  unsigned NumArgsToCopy = CI->getNumOperands()-1;
  if (NumArgsToCopy != ParamTys.size() &&
      !(NumArgsToCopy > ParamTys.size() &&
        Dest->getFunctionType()->isVarArg())) {
    std::cerr << "WARNING: Call arguments do not match expected number of"
              << " parameters.\n";
    std::cerr << "WARNING: In function '"
              << CI->getParent()->getParent()->getName() << "': call: " << *CI;
    std::cerr << "Function resolved to: ";
    WriteAsOperand(std::cerr, Dest);
    std::cerr << "\n";
    if (NumArgsToCopy > ParamTys.size())
      NumArgsToCopy = ParamTys.size();
  }

  std::vector<Value*> Params;

  // Convert all of the call arguments over... inserting cast instructions if
  // the types are not compatible.
  for (unsigned i = 1; i <= NumArgsToCopy; ++i) {
    Value *V = CI->getOperand(i);

    if (i-1 < ParamTys.size() && V->getType() != ParamTys[i-1]) {
      // Must insert a cast...
      V = new CastInst(V, ParamTys[i-1], "argcast", CI);
    }

    Params.push_back(V);
  }

  // Replace the old call instruction with a new call instruction that calls
  // the real function.
  //
  Instruction *NewCall = new CallInst(Dest, Params, "", CI);
  std::string Name = CI->getName(); CI->setName("");

  // Transfer the name over...
  if (NewCall->getType() != Type::VoidTy)
    NewCall->setName(Name);

  // Replace uses of the old instruction with the appropriate values...
  //
  if (NewCall->getType() == CI->getType()) {
    CI->replaceAllUsesWith(NewCall);
    NewCall->setName(Name);

  } else if (NewCall->getType() == Type::VoidTy) {
    // Resolved function does not return a value but the prototype does.  This
    // often occurs because undefined functions default to returning integers.
    // Just replace uses of the call (which are broken anyway) with dummy
    // values.
    CI->replaceAllUsesWith(Constant::getNullValue(CI->getType()));
  } else if (CI->getType() == Type::VoidTy) {
    // If we are gaining a new return value, we don't have to do anything
    // special here, because it will automatically be ignored.
  } else {
    // Insert a cast instruction to convert the return value of the function
    // into it's new type.  Of course we only need to do this if the return
    // value of the function is actually USED.
    //
    if (!CI->use_empty()) {
      // Insert the new cast instruction...
      CastInst *NewCast = new CastInst(NewCall, CI->getType(), Name, CI);
      CI->replaceAllUsesWith(NewCast);
    }
  }

  // The old instruction is no longer needed, destroy it!
  BB->getInstList().erase(CI);
}


static bool ResolveFunctions(Module &M, std::vector<GlobalValue*> &Globals,
                             Function *Concrete) {
  bool Changed = false;
  for (unsigned i = 0; i != Globals.size(); ++i)
    if (Globals[i] != Concrete) {
      Function *Old = cast<Function>(Globals[i]);
      const FunctionType *OldMT = Old->getFunctionType();
      const FunctionType *ConcreteMT = Concrete->getFunctionType();
      
      if (OldMT->getParamTypes().size() < ConcreteMT->getParamTypes().size() &&
          !ConcreteMT->isVarArg())
        if (!Old->use_empty()) {
          std::cerr << "WARNING: Linking function '" << Old->getName()
                    << "' is causing arguments to be dropped.\n";
          std::cerr << "WARNING: Prototype: ";
          WriteAsOperand(std::cerr, Old);
          std::cerr << " resolved to ";
          WriteAsOperand(std::cerr, Concrete);
          std::cerr << "\n";
        }
      
      // Check to make sure that if there are specified types, that they
      // match...
      //
      unsigned NumArguments = std::min(OldMT->getParamTypes().size(),
                                       ConcreteMT->getParamTypes().size());

      if (!Old->use_empty() && !Concrete->use_empty())
        for (unsigned i = 0; i < NumArguments; ++i)
          if (OldMT->getParamTypes()[i] != ConcreteMT->getParamTypes()[i]) {
            std::cerr << "WARNING: Function [" << Old->getName()
                      << "]: Parameter types conflict for: '" << OldMT
                      << "' and '" << ConcreteMT << "'\n";
            return Changed;
          }
      
      // Attempt to convert all of the uses of the old function to the
      // concrete form of the function.  If there is a use of the fn that
      // we don't understand here we punt to avoid making a bad
      // transformation.
      //
      // At this point, we know that the return values are the same for
      // our two functions and that the Old function has no varargs fns
      // specified.  In otherwords it's just <retty> (...)
      //
      for (unsigned i = 0; i < Old->use_size(); ) {
        User *U = *(Old->use_begin()+i);
        if (CastInst *CI = dyn_cast<CastInst>(U)) {
          // Convert casts directly
          assert(CI->getOperand(0) == Old);
          CI->setOperand(0, Concrete);
          Changed = true;
          ++NumResolved;
        } else if (CallInst *CI = dyn_cast<CallInst>(U)) {
          // Can only fix up calls TO the argument, not args passed in.
          if (CI->getCalledValue() == Old) {
            ConvertCallTo(CI, Concrete);
            Changed = true;
            ++NumResolved;
          } else {
            std::cerr << "Couldn't cleanup this function call, must be an"
                      << " argument or something!" << CI;
            ++i;
          }
        } else {
          std::cerr << "Cannot convert use of function: " << U << "\n";
          ++i;
        }
      }
    }
  return Changed;
}


static bool ResolveGlobalVariables(Module &M,
                                   std::vector<GlobalValue*> &Globals,
                                   GlobalVariable *Concrete) {
  bool Changed = false;
  assert(isa<ArrayType>(Concrete->getType()->getElementType()) &&
         "Concrete version should be an array type!");

  // Get the type of the things that may be resolved to us...
  const Type *AETy =
    cast<ArrayType>(Concrete->getType()->getElementType())->getElementType();

  std::vector<Constant*> Args;
  Args.push_back(Constant::getNullValue(Type::LongTy));
  Args.push_back(Constant::getNullValue(Type::LongTy));
  Constant *Replacement =
    ConstantExpr::getGetElementPtr(ConstantPointerRef::get(Concrete), Args);
  
  for (unsigned i = 0; i != Globals.size(); ++i)
    if (Globals[i] != Concrete) {
      GlobalVariable *Old = cast<GlobalVariable>(Globals[i]);
      if (Old->getType()->getElementType() != AETy) {
        std::cerr << "WARNING: Two global variables exist with the same name "
                  << "that cannot be resolved!\n";
        return false;
      }

      // In this case, Old is a pointer to T, Concrete is a pointer to array of
      // T.  Because of this, replace all uses of Old with a constantexpr
      // getelementptr that returns the address of the first element of the
      // array.
      //
      Old->replaceAllUsesWith(Replacement);
      // Since there are no uses of Old anymore, remove it from the module.
      M.getGlobalList().erase(Old);

      ++NumGlobals;
      Changed = true;
    }
  return Changed;
}

static bool ProcessGlobalsWithSameName(Module &M,
                                       std::vector<GlobalValue*> &Globals) {
  assert(!Globals.empty() && "Globals list shouldn't be empty here!");

  bool isFunction = isa<Function>(Globals[0]);   // Is this group all functions?
  bool Changed = false;
  GlobalValue *Concrete = 0;  // The most concrete implementation to resolve to

  assert((isFunction ^ isa<GlobalVariable>(Globals[0])) &&
         "Should either be function or gvar!");

  for (unsigned i = 0; i != Globals.size(); ) {
    if (isa<Function>(Globals[i]) != isFunction) {
      std::cerr << "WARNING: Found function and global variable with the "
                << "same name: '" << Globals[i]->getName() << "'.\n";
      return false;                 // Don't know how to handle this, bail out!
    }

    if (isFunction) {
      // For functions, we look to merge functions definitions of "int (...)"
      // to 'int (int)' or 'int ()' or whatever else is not completely generic.
      //
      Function *F = cast<Function>(Globals[i]);
      if (!F->isExternal()) {
        if (Concrete && !Concrete->isExternal())
          return false;   // Found two different functions types.  Can't choose!
        
        Concrete = Globals[i];
      } else if (Concrete) {
        if (Concrete->isExternal()) // If we have multiple external symbols...x
          if (F->getFunctionType()->getNumParams() > 
              cast<Function>(Concrete)->getFunctionType()->getNumParams())
            Concrete = F;  // We are more concrete than "Concrete"!

      } else {
        Concrete = F;
      }
      ++i;
    } else {
      // For global variables, we have to merge C definitions int A[][4] with
      // int[6][4]
      GlobalVariable *GV = cast<GlobalVariable>(Globals[i]);
      if (Concrete == 0) {
        if (isa<ArrayType>(GV->getType()->getElementType()))
          Concrete = GV;
      } else {    // Must have different types... one is an array of the other?
        const ArrayType *AT =
          dyn_cast<ArrayType>(GV->getType()->getElementType());

        // If GV is an array of Concrete, then GV is the array.
        if (AT && AT->getElementType() == Concrete->getType()->getElementType())
          Concrete = GV;
        else {
          // Concrete must be an array type, check to see if the element type of
          // concrete is already GV.
          AT = cast<ArrayType>(Concrete->getType()->getElementType());
          if (AT->getElementType() != GV->getType()->getElementType())
            Concrete = 0;           // Don't know how to handle it!
        }
      }
      
      ++i;
    }
  }

  if (Globals.size() > 1) {         // Found a multiply defined global...
    // We should find exactly one concrete function definition, which is
    // probably the implementation.  Change all of the function definitions and
    // uses to use it instead.
    //
    if (!Concrete) {
      std::cerr << "WARNING: Found function types that are not compatible:\n";
      for (unsigned i = 0; i < Globals.size(); ++i) {
        std::cerr << "\t" << Globals[i]->getType()->getDescription() << " %"
                  << Globals[i]->getName() << "\n";
      }
      std::cerr << "  No linkage of globals named '" << Globals[0]->getName()
                << "' performed!\n";
      return Changed;
    }

    if (isFunction)
      return Changed | ResolveFunctions(M, Globals, cast<Function>(Concrete));
    else
      return Changed | ResolveGlobalVariables(M, Globals,
                                              cast<GlobalVariable>(Concrete));
  }
  return Changed;
}

bool FunctionResolvingPass::run(Module &M) {
  SymbolTable &ST = M.getSymbolTable();

  std::map<std::string, std::vector<GlobalValue*> > Globals;

  // Loop over the entries in the symbol table. If an entry is a func pointer,
  // then add it to the Functions map.  We do a two pass algorithm here to avoid
  // problems with iterators getting invalidated if we did a one pass scheme.
  //
  for (SymbolTable::iterator I = ST.begin(), E = ST.end(); I != E; ++I)
    if (const PointerType *PT = dyn_cast<PointerType>(I->first)) {
      SymbolTable::VarMap &Plane = I->second;
      for (SymbolTable::type_iterator PI = Plane.begin(), PE = Plane.end();
           PI != PE; ++PI) {
        GlobalValue *GV = cast<GlobalValue>(PI->second);
        assert(PI->first == GV->getName() &&
               "Global name and symbol table do not agree!");
        if (GV->hasExternalLinkage())  // Only resolve decls to external fns
          Globals[PI->first].push_back(GV);
      }
    }

  bool Changed = false;

  // Now we have a list of all functions with a particular name.  If there is
  // more than one entry in a list, merge the functions together.
  //
  for (std::map<std::string, std::vector<GlobalValue*> >::iterator
         I = Globals.begin(), E = Globals.end(); I != E; ++I)
    Changed |= ProcessGlobalsWithSameName(M, I->second);

  // Now loop over all of the globals, checking to see if any are trivially
  // dead.  If so, remove them now.

  for (Module::iterator I = M.begin(), E = M.end(); I != E; )
    if (I->isExternal() && I->use_empty()) {
      Function *F = I;
      ++I;
      M.getFunctionList().erase(F);
      ++NumResolved;
      Changed = true;
    } else {
      ++I;
    }

  for (Module::giterator I = M.gbegin(), E = M.gend(); I != E; )
    if (I->isExternal() && I->use_empty()) {
      GlobalVariable *GV = I;
      ++I;
      M.getGlobalList().erase(GV);
      ++NumGlobals;
      Changed = true;
    } else {
      ++I;
    }

  return Changed;
}
