llvm/lib/Transforms/Utils/CloneModule.cpp

//===- CloneModule.cpp - Clone an entire module ---------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the CloneModule interface which makes a copy of an
// entire module.
//
//===----------------------------------------------------------------------===//

#include "llvm/IR/Constant.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Module.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/ValueMapper.h"
using namespace llvm;

static void copyComdat(GlobalObject *Dst, const GlobalObject *Src) {
  const Comdat *SC = Src->getComdat();
  if (!SC)
    return;
  Comdat *DC = Dst->getParent()->getOrInsertComdat(SC->getName());
  DC->setSelectionKind(SC->getSelectionKind());
  Dst->setComdat(DC);
}

/// This is not as easy as it might seem because we have to worry about making
/// copies of global variables and functions, and making their (initializers and
/// references, respectively) refer to the right globals.
///
std::unique_ptr<Module> llvm::CloneModule(const Module &M) {
  // Create the value map that maps things from the old module over to the new
  // module.
  ValueToValueMapTy VMap;
  return CloneModule(M, VMap);
}

std::unique_ptr<Module> llvm::CloneModule(const Module &M,
                                          ValueToValueMapTy &VMap) {
  return CloneModule(M, VMap, [](const GlobalValue *GV) { return true; });
}

std::unique_ptr<Module> llvm::CloneModule(
    const Module &M, ValueToValueMapTy &VMap,
    function_ref<bool(const GlobalValue *)> ShouldCloneDefinition) {
  // First off, we need to create the new module.
  std::unique_ptr<Module> New =
      llvm::make_unique<Module>(M.getModuleIdentifier(), M.getContext());
  New->setDataLayout(M.getDataLayout());
  New->setTargetTriple(M.getTargetTriple());
  New->setModuleInlineAsm(M.getModuleInlineAsm());

  // Loop over all of the global variables, making corresponding globals in the
  // new module.  Here we add them to the VMap and to the new Module.  We
  // don't worry about attributes or initializers, they will come later.
  //
  for (Module::const_global_iterator I = M.global_begin(), E = M.global_end();
       I != E; ++I) {
    GlobalVariable *GV = new GlobalVariable(*New, 
                                            I->getValueType(),
                                            I->isConstant(), I->getLinkage(),
                                            (Constant*) nullptr, I->getName(),
                                            (GlobalVariable*) nullptr,
                                            I->getThreadLocalMode(),
                                            I->getType()->getAddressSpace());
    GV->copyAttributesFrom(&*I);
    VMap[&*I] = GV;
  }

  // Loop over the functions in the module, making external functions as before
  for (const Function &I : M) {
    Function *NF = Function::Create(cast<FunctionType>(I.getValueType()),
                                    I.getLinkage(), I.getName(), New.get());
    NF->copyAttributesFrom(&I);
    VMap[&I] = NF;
  }

  // Loop over the aliases in the module
  for (Module::const_alias_iterator I = M.alias_begin(), E = M.alias_end();
       I != E; ++I) {
    if (!ShouldCloneDefinition(&*I)) {
      // An alias cannot act as an external reference, so we need to create
      // either a function or a global variable depending on the value type.
      // FIXME: Once pointee types are gone we can probably pick one or the
      // other.
      GlobalValue *GV;
      if (I->getValueType()->isFunctionTy())
        GV = Function::Create(cast<FunctionType>(I->getValueType()),
                              GlobalValue::ExternalLinkage, I->getName(),
                              New.get());
      else
        GV = new GlobalVariable(
            *New, I->getValueType(), false, GlobalValue::ExternalLinkage,
            nullptr, I->getName(), nullptr,
            I->getThreadLocalMode(), I->getType()->getAddressSpace());
      VMap[&*I] = GV;
      // We do not copy attributes (mainly because copying between different
      // kinds of globals is forbidden), but this is generally not required for
      // correctness.
      continue;
    }
    auto *GA = GlobalAlias::create(I->getValueType(),
                                   I->getType()->getPointerAddressSpace(),
                                   I->getLinkage(), I->getName(), New.get());
    GA->copyAttributesFrom(&*I);
    VMap[&*I] = GA;
  }
  
  // Now that all of the things that global variable initializer can refer to
  // have been created, loop through and copy the global variable referrers
  // over...  We also set the attributes on the global now.
  //
  for (Module::const_global_iterator I = M.global_begin(), E = M.global_end();
       I != E; ++I) {
    if (I->isDeclaration())
      continue;

    GlobalVariable *GV = cast<GlobalVariable>(VMap[&*I]);
    if (!ShouldCloneDefinition(&*I)) {
      // Skip after setting the correct linkage for an external reference.
      GV->setLinkage(GlobalValue::ExternalLinkage);
      continue;
    }
    if (I->hasInitializer())
      GV->setInitializer(MapValue(I->getInitializer(), VMap));

    SmallVector<std::pair<unsigned, MDNode *>, 1> MDs;
    I->getAllMetadata(MDs);
    for (auto MD : MDs)
      GV->addMetadata(MD.first,
                      *MapMetadata(MD.second, VMap, RF_MoveDistinctMDs));

    copyComdat(GV, &*I);
  }

  // Similarly, copy over function bodies now...
  //
  for (const Function &I : M) {
    if (I.isDeclaration())
      continue;

    Function *F = cast<Function>(VMap[&I]);
    if (!ShouldCloneDefinition(&I)) {
      // Skip after setting the correct linkage for an external reference.
      F->setLinkage(GlobalValue::ExternalLinkage);
      // Personality function is not valid on a declaration.
      F->setPersonalityFn(nullptr);
      continue;
    }

    Function::arg_iterator DestI = F->arg_begin();
    for (Function::const_arg_iterator J = I.arg_begin(); J != I.arg_end();
         ++J) {
      DestI->setName(J->getName());
      VMap[&*J] = &*DestI++;
    }

    SmallVector<ReturnInst *, 8> Returns; // Ignore returns cloned.
    CloneFunctionInto(F, &I, VMap, /*ModuleLevelChanges=*/true, Returns);

    if (I.hasPersonalityFn())
      F->setPersonalityFn(MapValue(I.getPersonalityFn(), VMap));

    copyComdat(F, &I);
  }

  // And aliases
  for (Module::const_alias_iterator I = M.alias_begin(), E = M.alias_end();
       I != E; ++I) {
    // We already dealt with undefined aliases above.
    if (!ShouldCloneDefinition(&*I))
      continue;
    GlobalAlias *GA = cast<GlobalAlias>(VMap[&*I]);
    if (const Constant *C = I->getAliasee())
      GA->setAliasee(MapValue(C, VMap));
  }

  // And named metadata....
  for (Module::const_named_metadata_iterator I = M.named_metadata_begin(),
                                             E = M.named_metadata_end();
       I != E; ++I) {
    const NamedMDNode &NMD = *I;
    NamedMDNode *NewNMD = New->getOrInsertNamedMetadata(NMD.getName());
    for (unsigned i = 0, e = NMD.getNumOperands(); i != e; ++i)
      NewNMD->addOperand(MapMetadata(NMD.getOperand(i), VMap));
  }

  return New;
}

extern "C" {

LLVMModuleRef LLVMCloneModule(LLVMModuleRef M) {
  return wrap(CloneModule(*unwrap(M)).release());
}

}