path: root/lib/Transforms/IPO/FunctionResolution.cpp

//===- FunctionResolution.cpp - Resolve declarations to implementations ---===//
// 
//                     The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
// 
//===----------------------------------------------------------------------===//
//
// 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/DerivedTypes.h"
#include "llvm/Pass.h"
#include "llvm/Instructions.h"
#include "llvm/Constants.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/ADT/Statistic.h"
#include <algorithm>
using namespace llvm;

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

  struct FunctionResolvingPass : public Pass {
    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
      AU.addRequired<TargetData>();
    }

    bool run(Module &M);
  };
  RegisterOpt<FunctionResolvingPass> X("funcresolve", "Resolve Functions");
}

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

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->getNumParams() > ConcreteMT->getNumParams() &&
          !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->getNumParams(),
                                       ConcreteMT->getNumParams());

      if (!Old->use_empty() && !Concrete->use_empty())
        for (unsigned i = 0; i < NumArguments; ++i)
          if (OldMT->getParamType(i) != ConcreteMT->getParamType(i))
            if (OldMT->getParamType(i)->getTypeID() != 
                ConcreteMT->getParamType(i)->getTypeID()) {
              std::cerr << "WARNING: Function [" << Old->getName()
                        << "]: Parameter types conflict for: '";
              WriteTypeSymbolic(std::cerr, OldMT, &M);
              std::cerr << "' and '";
              WriteTypeSymbolic(std::cerr, ConcreteMT, &M);
              std::cerr << "'\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> (...)
      //
      if (!Old->use_empty()) {  // Avoid making the CPR unless we really need it
        Value *Replacement = Concrete;
        if (Concrete->getType() != Old->getType())
          Replacement = ConstantExpr::getCast(Concrete,Old->getType());
        NumResolved += Old->use_size();
        Old->replaceAllUsesWith(Replacement);
      }

      // Since there are no uses of Old anymore, remove it from the module.
      M.getFunctionList().erase(Old);
    }
  return Changed;
}


static bool ResolveGlobalVariables(Module &M,
                                   std::vector<GlobalValue*> &Globals,
                                   GlobalVariable *Concrete) {
  bool Changed = false;

  for (unsigned i = 0; i != Globals.size(); ++i)
    if (Globals[i] != Concrete) {
      Constant *Cast = ConstantExpr::getCast(Concrete, Globals[i]->getType());
      Globals[i]->replaceAllUsesWith(Cast);

      // Since there are no uses of Old anymore, remove it from the module.
      M.getGlobalList().erase(cast<GlobalVariable>(Globals[i]));

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

// Check to see if all of the callers of F ignore the return value.
static bool CallersAllIgnoreReturnValue(Function &F) {
  if (F.getReturnType() == Type::VoidTy) return true;
  for (Value::use_iterator I = F.use_begin(), E = F.use_end(); I != E; ++I) {
    if (GlobalValue *GV = dyn_cast<GlobalValue>(*I)) {
      for (Value::use_iterator I = GV->use_begin(), E = GV->use_end();
           I != E; ++I) {
        CallSite CS = CallSite::get(*I);
        if (!CS.getInstruction() || !CS.getInstruction()->use_empty())
          return false;
      }
    } else {
      CallSite CS = CallSite::get(*I);
      if (!CS.getInstruction() || !CS.getInstruction()->use_empty())
        return false;
    }
  }
  return true;
}

static bool ProcessGlobalsWithSameName(Module &M, TargetData &TD,
                                       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?
  GlobalValue *Concrete = 0;  // The most concrete implementation to resolve to

  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...
          if (F->getFunctionType()->getNumParams() > 
              cast<Function>(Concrete)->getFunctionType()->getNumParams())
            Concrete = F;  // We are more concrete than "Concrete"!

      } else {
        Concrete = F;
      }
    } else {
      GlobalVariable *GV = cast<GlobalVariable>(Globals[i]);
      if (!GV->isExternal()) {
        if (Concrete) {
          std::cerr << "WARNING: Two global variables with external linkage"
                    << " exist with the same name: '" << GV->getName()
                    << "'!\n";
          return false;
        }
        Concrete = GV;
      }
    }
    ++i;
  }

  if (Globals.size() > 1) {         // Found a multiply defined global...
    // If there are no external declarations, and there is at most one
    // externally visible instance of the global, then there is nothing to do.
    //
    bool HasExternal = false;