ValueMapper: Eliminate cross-file co-recursion, NFC

Eliminate co-recursion of Mapper::mapValue through
ValueMaterializer::materializeInitFor, through a major redesign of the
ValueMapper.cpp interface.

  - Expose a ValueMapper class that controls the entry points to the
    mapping algorithms.
  - Change IRLinker to use ValueMapper directly, rather than
    llvm::RemapInstruction, llvm::MapValue, etc.
  - Use (e.g.) ValueMapper::scheduleMapGlobalInit to add mapping work to
    a worklist in ValueMapper instead of recursing.

There were two fairly major complications.

Firstly, IRLinker::linkAppendingVarProto incorporates an on-the-fly IR
ugprade that I had to split apart.  Long-term, this upgrade should be
done in the bitcode reader (and we should only accept the "new" form),
but for now I've just made it work and added a FIXME.  The hold-op is
that we need to deprecate C API that relies on this.

Secondly, IRLinker has special logic to correctly implement aliases with
comdats, and uses two ValueToValueMapTy instances and two
ValueMaterializers.  I supported this by allowing clients to register an
alternate mapping context, whose MCID can be passed in when scheduling
new work.

While out of scope for this commit, it should now be straightforward to
remove recursion from Mapper::mapValue.

llvm-svn: 266503

2 files changed, 327 insertions, 99 deletions

diff --git a/llvm/lib/Linker/IRMover.cpp b/llvm/lib/Linker/IRMover.cpp
index e4121fedc0a..64c73235777 100644
--- a/llvm/lib/Linker/IRMover.cpp
+++ b/llvm/lib/Linker/IRMover.cpp
@@ -397,8 +397,9 @@ class IRLinker {
 
   bool HasError = false;
 
-  /// Flags to pass to value mapper invocations.
-  RemapFlags ValueMapperFlags = RF_MoveDistinctMDs | RF_IgnoreMissingLocals;
+  /// Entry point for mapping values and alternate context for mapping aliases.
+  ValueMapper Mapper;
+  unsigned AliasMCID;
 
   /// Handles cloning of a global values from the source module into
   /// the destination module, including setting the attributes and visibility.
@@ -470,7 +471,11 @@ public:
            std::unique_ptr<Module> SrcM, ArrayRef<GlobalValue *> ValuesToLink,
            std::function<void(GlobalValue &, IRMover::ValueAdder)> AddLazyFor)
       : DstM(DstM), SrcM(std::move(SrcM)), AddLazyFor(AddLazyFor), TypeMap(Set),
-        GValMaterializer(*this), LValMaterializer(*this) {
+        GValMaterializer(*this), LValMaterializer(*this),
+        Mapper(ValueMap, RF_MoveDistinctMDs | RF_IgnoreMissingLocals, &TypeMap,
+               &GValMaterializer),
+        AliasMCID(Mapper.registerAlternateMappingContext(AliasValueMap,
+                                                         &LValMaterializer)) {
     for (GlobalValue *GV : ValuesToLink)
       maybeAdd(GV);
   }
@@ -712,6 +717,10 @@ Constant *IRLinker::linkAppendingVarProto(GlobalVariable *DstGV,
   Type *EltTy = cast<ArrayType>(TypeMap.get(SrcGV->getValueType()))
                     ->getElementType();
 
+  // FIXME: This upgrade is done during linking to support the C API.  Once the
+  // old form is deprecated, we should move this upgrade to
+  // llvm::UpgradeGlobalVariable() and simplify the logic here and in
+  // Mapper::mapAppendingVariable() in ValueMapper.cpp.
   StringRef Name = SrcGV->getName();
   bool IsNewStructor = false;
   bool IsOldStructor = false;
@@ -729,8 +738,10 @@ Constant *IRLinker::linkAppendingVarProto(GlobalVariable *DstGV,
     EltTy = StructType::get(SrcGV->getContext(), Tys, false);
   }
 
+  uint64_t DstNumElements = 0;
   if (DstGV) {
     ArrayType *DstTy = cast<ArrayType>(DstGV->getValueType());
+    DstNumElements = DstTy->getNumElements();
 
     if (!SrcGV->hasAppendingLinkage() || !DstGV->hasAppendingLinkage()) {
       emitError(
@@ -774,10 +785,6 @@ Constant *IRLinker::linkAppendingVarProto(GlobalVariable *DstGV,
     }
   }
 
-  SmallVector<Constant *, 16> DstElements;
-  if (DstGV)
-    getArrayElements(DstGV->getInitializer(), DstElements);
-
   SmallVector<Constant *, 16> SrcElements;
   getArrayElements(SrcGV->getInitializer(), SrcElements);
 
@@ -793,7 +800,7 @@ Constant *IRLinker::linkAppendingVarProto(GlobalVariable *DstGV,
                          return !shouldLink(DGV, *Key);
                        }),
         SrcElements.end());
-  uint64_t NewSize = DstElements.size() + SrcElements.size();
+  uint64_t NewSize = DstNumElements + SrcElements.size();
   ArrayType *NewType = ArrayType::get(EltTy, NewSize);
 
   // Create the new global variable.
@@ -810,25 +817,9 @@ Constant *IRLinker::linkAppendingVarProto(GlobalVariable *DstGV,
   // Stop recursion.
   ValueMap[SrcGV] = Ret;
 
-  for (auto *V : SrcElements) {
-    Constant *NewV;
-    if (IsOldStructor) {
-      auto *S = cast<ConstantStruct>(V);
-      auto *E1 = MapValue(S->getOperand(0), ValueMap, ValueMapperFlags,
-                          &TypeMap, &GValMaterializer);
-      auto *E2 = MapValue(S->getOperand(1), ValueMap, ValueMapperFlags,
-                          &TypeMap, &GValMaterializer);
-      Value *Null = Constant::getNullValue(VoidPtrTy);
-      NewV =
-          ConstantStruct::get(cast<StructType>(EltTy), E1, E2, Null, nullptr);
-    } else {
-      NewV =
-          MapValue(V, ValueMap, ValueMapperFlags, &TypeMap, &GValMaterializer);
-    }
-    DstElements.push_back(NewV);
-  }
-
-  NG->setInitializer(ConstantArray::get(NewType, DstElements));
+  Mapper.scheduleMapAppendingVariable(*NG,
+                                      DstGV ? DstGV->getInitializer() : nullptr,
+                                      IsOldStructor, SrcElements);
 
   // Replace any uses of the two global variables with uses of the new
   // global.
@@ -935,8 +926,7 @@ Constant *IRLinker::linkGlobalValueProto(GlobalValue *SGV, bool ForAlias) {
 /// referenced are in Dest.
 void IRLinker::linkGlobalInit(GlobalVariable &Dst, GlobalVariable &Src) {
   // Figure out what the initializer looks like in the dest module.
-  Dst.setInitializer(MapValue(Src.getInitializer(), ValueMap, ValueMapperFlags,
-                              &TypeMap, &GValMaterializer));
+  Mapper.scheduleMapGlobalInitializer(Dst, *Src.getInitializer());
 }
 
 /// Copy the source function over into the dest function and fix up references
@@ -968,15 +958,12 @@ bool IRLinker::linkFunctionBody(Function &Dst, Function &Src) {
   Dst.getBasicBlockList().splice(Dst.end(), Src.getBasicBlockList());
 
   // Everything has been moved over.  Remap it.
-  RemapFunction(Dst, ValueMap, ValueMapperFlags, &TypeMap, &GValMaterializer);
+  Mapper.scheduleRemapFunction(Dst);
   return false;
 }
 
 void IRLinker::linkAliasBody(GlobalAlias &Dst, GlobalAlias &Src) {
-  Constant *Aliasee = Src.getAliasee();
-  Constant *Val = MapValue(Aliasee, AliasValueMap, ValueMapperFlags, &TypeMap,
-                           &LValMaterializer);
-  Dst.setAliasee(Val);
+  Mapper.scheduleMapGlobalAliasee(Dst, *Src.getAliasee(), AliasMCID);
 }
 
 bool IRLinker::linkGlobalValueBody(GlobalValue &Dst, GlobalValue &Src) {
@@ -1000,9 +987,7 @@ void IRLinker::linkNamedMDNodes() {
     NamedMDNode *DestNMD = DstM.getOrInsertNamedMetadata(NMD.getName());
     // Add Src elements into Dest node.
     for (const MDNode *Op : NMD.operands())
-      DestNMD->addOperand(MapMetadata(
-          Op, ValueMap, ValueMapperFlags | RF_NullMapMissingGlobalValues,
-          &TypeMap, &GValMaterializer));
+      DestNMD->addOperand(Mapper.mapMDNode(*Op));
   }
 }
 
@@ -1242,7 +1227,7 @@ bool IRLinker::run() {
       continue;
 
     assert(!GV->isDeclaration());
-    MapValue(GV, ValueMap, ValueMapperFlags, &TypeMap, &GValMaterializer);
+    Mapper.mapValue(*GV);
     if (HasError)
       return true;
   }
@@ -1250,6 +1235,7 @@ bool IRLinker::run() {
   // Note that we are done linking global value bodies. This prevents
   // metadata linking from creating new references.
   DoneLinkingBodies = true;
+  Mapper.addFlags(RF_NullMapMissingGlobalValues);
 
   // Remap all of the named MDNodes in Src into the DstM module. We do this
   // after linking GlobalValues so that MDNodes that reference GlobalValues
diff --git a/llvm/lib/Transforms/Utils/ValueMapper.cpp b/llvm/lib/Transforms/Utils/ValueMapper.cpp
index 102f641ebfc..db984eef59c 100644
--- a/llvm/lib/Transforms/Utils/ValueMapper.cpp
+++ b/llvm/lib/Transforms/Utils/ValueMapper.cpp
@@ -16,6 +16,8 @@
 #include "llvm/IR/CallSite.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/Function.h"
+#include "llvm/IR/GlobalAlias.h"
+#include "llvm/IR/GlobalVariable.h"
 #include "llvm/IR/InlineAsm.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/Metadata.h"
@@ -30,14 +32,6 @@ void ValueMaterializer::materializeInitFor(GlobalValue *New, GlobalValue *Old) {
 
 namespace {
 
-/// A GlobalValue whose initializer needs to be materialized.
-struct DelayedGlobalValueInit {
-  GlobalValue *Old;
-  GlobalValue *New;
-  DelayedGlobalValueInit(const GlobalValue *Old, GlobalValue *New)
-      : Old(const_cast<GlobalValue *>(Old)), New(New) {}
-};
-
 /// A basic block used in a BlockAddress whose function body is not yet
 /// materialized.
 struct DelayedBasicBlock {
@@ -58,30 +52,88 @@ struct DelayedBasicBlock {
         TempBB(BasicBlock::Create(Old.getContext())) {}
 };
 
+struct WorklistEntry {
+  enum EntryKind {
+    MapGlobalInit,
+    MapAppendingVar,
+    MapGlobalAliasee,
+    RemapFunction
+  };
+  struct GVInitTy {
+    GlobalVariable *GV;
+    Constant *Init;
+  };
+  struct AppendingGVTy {
+    GlobalVariable *GV;
+    Constant *InitPrefix;
+  };
+  struct GlobalAliaseeTy {
+    GlobalAlias *GA;
+    Constant *Aliasee;
+  };
+
+  unsigned Kind : 2;
+  unsigned MCID : 29;
+  unsigned AppendingGVIsOldCtorDtor : 1;
+  unsigned AppendingGVNumNewMembers;
+  union {
+    GVInitTy GVInit;
+    AppendingGVTy AppendingGV;
+    GlobalAliaseeTy GlobalAliasee;
+    Function *RemapF;
+  } Data;
+};
+
+struct MappingContext {
+  ValueToValueMapTy *VM;
+  ValueMaterializer *Materializer = nullptr;
+
+  /// Construct a MappingContext with a value map and materializer.
+  explicit MappingContext(ValueToValueMapTy &VM,
+                          ValueMaterializer *Materializer = nullptr)
+      : VM(&VM), Materializer(Materializer) {}
+};
+
 class MDNodeMapper;
 class Mapper {
   friend class MDNodeMapper;
 
-  ValueToValueMapTy *VM;
   RemapFlags Flags;
   ValueMapTypeRemapper *TypeMapper;
-  ValueMaterializer *Materializer;
-
-  SmallVector<DelayedGlobalValueInit, 8> DelayedInits;
+  unsigned CurrentMCID = 0;
+  SmallVector<MappingContext, 2> MCs;
+  SmallVector<WorklistEntry, 4> Worklist;
   SmallVector<DelayedBasicBlock, 1> DelayedBBs;
+  SmallVector<Constant *, 16> AppendingInits;
 
 public:
   Mapper(ValueToValueMapTy &VM, RemapFlags Flags,
          ValueMapTypeRemapper *TypeMapper, ValueMaterializer *Materializer)
-      : VM(&VM), Flags(Flags), TypeMapper(TypeMapper),
-        Materializer(Materializer) {}
+      : Flags(Flags), TypeMapper(TypeMapper),
+        MCs(1, MappingContext(VM, Materializer)) {}
 
-  ~Mapper();
+  /// ValueMapper should explicitly call \a flush() before destruction.
+  ~Mapper() { assert(!hasWorkToDo() && "Expected to be flushed"); }
+
+  bool hasWorkToDo() const { return !Worklist.empty(); }
+
+  unsigned
+  registerAlternateMappingContext(ValueToValueMapTy &VM,
+                                  ValueMaterializer *Materializer = nullptr) {
+    MCs.push_back(MappingContext(VM, Materializer));
+    return MCs.size() - 1;
+  }
+
+  void addFlags(RemapFlags Flags);
 
   Value *mapValue(const Value *V);
   void remapInstruction(Instruction *I);
   void remapFunction(Function &F);
 
+  Constant *mapConstant(const Constant *C) {
+    return cast_or_null<Constant>(mapValue(C));
+  }
+
   /// Map metadata.
   ///
   /// Find the mapping for MD.  Guarantees that the return will be resolved
@@ -102,8 +154,28 @@ public:
   // through metadata operands, always return nullptr on unmapped locals.
   Metadata *mapLocalAsMetadata(const LocalAsMetadata &LAM);
 
+  void scheduleMapGlobalInitializer(GlobalVariable &GV, Constant &Init,
+                                    unsigned MCID);
+  void scheduleMapAppendingVariable(GlobalVariable &GV, Constant *InitPrefix,
+                                    bool IsOldCtorDtor,
+                                    ArrayRef<Constant *> NewMembers,
+                                    unsigned MCID);
+  void scheduleMapGlobalAliasee(GlobalAlias &GA, Constant &Aliasee,
+                                unsigned MCID);
+  void scheduleRemapFunction(Function &F, unsigned MCID);
+
+  void flush();
+
 private:
-  ValueToValueMapTy &getVM() { return *VM; }
+  void mapGlobalInitializer(GlobalVariable &GV, Constant &Init);
+  void mapAppendingVariable(GlobalVariable &GV, Constant *InitPrefix,
+                            bool IsOldCtorDtor,
+                            ArrayRef<Constant *> NewMembers);
+  void mapGlobalAliasee(GlobalAlias &GA, Constant &Aliasee);
+  void remapFunction(Function &F, ValueToValueMapTy &VM);
+
+  ValueToValueMapTy &getVM() { return *MCs[CurrentMCID].VM; }
+  ValueMaterializer *getMaterializer() { return MCs[CurrentMCID].Materializer; }
 
   Value *mapBlockAddress(const BlockAddress &BA);
 
@@ -264,12 +336,6 @@ private:
 
 } // end namespace
 
-Value *llvm::MapValue(const Value *V, ValueToValueMapTy &VM, RemapFlags Flags,
-                      ValueMapTypeRemapper *TypeMapper,
-                      ValueMaterializer *Materializer) {
-  return Mapper(VM, Flags, TypeMapper, Materializer).mapValue(V);
-}
-
 Value *Mapper::mapValue(const Value *V) {
   ValueToValueMapTy::iterator I = getVM().find(V);
 
@@ -278,13 +344,13 @@ Value *Mapper::mapValue(const Value *V) {
     return I->second;
 
   // If we have a materializer and it can materialize a value, use that.
-  if (Materializer) {
+  if (auto *Materializer = getMaterializer()) {
     if (Value *NewV =
             Materializer->materializeDeclFor(const_cast<Value *>(V))) {
       getVM()[V] = NewV;
       if (auto *NewGV = dyn_cast<GlobalValue>(NewV))
-        DelayedInits.push_back(
-            DelayedGlobalValueInit(cast<GlobalValue>(V), NewGV));
+        Materializer->materializeInitFor(
+            NewGV, cast<GlobalValue>(const_cast<Value *>(V)));
       return NewV;
     }
   }
@@ -684,12 +750,6 @@ Optional<Metadata *> Mapper::mapSimpleMetadata(const Metadata *MD) {
   return None;
 }
 
-Metadata *llvm::MapMetadata(const Metadata *MD, ValueToValueMapTy &VM,
-                            RemapFlags Flags, ValueMapTypeRemapper *TypeMapper,
-                            ValueMaterializer *Materializer) {
-  return Mapper(VM, Flags, TypeMapper, Materializer).mapMetadata(MD);
-}
-
 Metadata *Mapper::mapLocalAsMetadata(const LocalAsMetadata &LAM) {
   // Lookup the mapping for the value itself, and return the appropriate
   // metadata.
@@ -716,36 +776,42 @@ Metadata *Mapper::mapMetadata(const Metadata *MD) {
   return MDNodeMapper(*this).map(*cast<MDNode>(MD));
 }
 
-Mapper::~Mapper() {
-  // Materialize global initializers.
-  while (!DelayedInits.empty()) {
-    auto Init = DelayedInits.pop_back_val();
-    Materializer->materializeInitFor(Init.New, Init.Old);
+void Mapper::flush() {
+  // Flush out the worklist of global values.
+  while (!Worklist.empty()) {
+    WorklistEntry E = Worklist.pop_back_val();
+    CurrentMCID = E.MCID;
+    switch (E.Kind) {
+    case WorklistEntry::MapGlobalInit:
+      E.Data.GVInit.GV->setInitializer(mapConstant(E.Data.GVInit.Init));
+      break;
+    case WorklistEntry::MapAppendingVar: {
+      unsigned PrefixSize = AppendingInits.size() - E.AppendingGVNumNewMembers;
+      mapAppendingVariable(*E.Data.AppendingGV.GV,
+                           E.Data.AppendingGV.InitPrefix,
+                           E.AppendingGVIsOldCtorDtor,
+                           makeArrayRef(AppendingInits).slice(PrefixSize));
+      AppendingInits.resize(PrefixSize);
+      break;
+    }
+    case WorklistEntry::MapGlobalAliasee:
+      E.Data.GlobalAliasee.GA->setAliasee(
+          mapConstant(E.Data.GlobalAliasee.Aliasee));
+      break;
+    case WorklistEntry::RemapFunction:
+      remapFunction(*E.Data.RemapF);
+      break;
+    }
   }
+  CurrentMCID = 0;
 
-  // Process block addresses delayed until global inits.
+  // Finish logic for block addresses now that all global values have been
+  // handled.
   while (!DelayedBBs.empty()) {
     DelayedBasicBlock DBB = DelayedBBs.pop_back_val();
     BasicBlock *BB = cast_or_null<BasicBlock>(mapValue(DBB.OldBB));
     DBB.TempBB->replaceAllUsesWith(BB ? BB : DBB.OldBB);
   }
-
-  // We don't expect these to grow after clearing.
-  assert(DelayedInits.empty());
-  assert(DelayedBBs.empty());
-}
-
-MDNode *llvm::MapMetadata(const MDNode *MD, ValueToValueMapTy &VM,
-                          RemapFlags Flags, ValueMapTypeRemapper *TypeMapper,
-                          ValueMaterializer *Materializer) {
-  return cast_or_null<MDNode>(MapMetadata(static_cast<const Metadata *>(MD), VM,
-                                          Flags, TypeMapper, Materializer));
-}
-
-void llvm::RemapInstruction(Instruction *I, ValueToValueMapTy &VM,
-                            RemapFlags Flags, ValueMapTypeRemapper *TypeMapper,
-                            ValueMaterializer *Materializer) {
-  Mapper(VM, Flags, TypeMapper, Materializer).remapInstruction(I);
 }
 
 void Mapper::remapInstruction(Instruction *I) {
@@ -782,7 +848,7 @@ void Mapper::remapInstruction(Instruction *I) {
     if (New != Old)
       I->setMetadata(MI.first, New);
   }
-  
+
   if (!TypeMapper)
     return;
 
@@ -808,12 +874,6 @@ void Mapper::remapInstruction(Instruction *I) {
   I->mutateType(TypeMapper->remapType(I->getType()));
 }
 
-void llvm::RemapFunction(Function &F, ValueToValueMapTy &VM, RemapFlags Flags,
-                         ValueMapTypeRemapper *TypeMapper,
-                         ValueMaterializer *Materializer) {
-  Mapper(VM, Flags, TypeMapper, Materializer).remapFunction(F);
-}
-
 void Mapper::remapFunction(Function &F) {
   // Remap the operands.
   for (Use &Op : F.operands())
@@ -836,3 +896,185 @@ void Mapper::remapFunction(Function &F) {
     for (Instruction &I : BB)
       remapInstruction(&I);
 }
+
+void Mapper::mapAppendingVariable(GlobalVariable &GV, Constant *InitPrefix,
+                                  bool IsOldCtorDtor,
+                                  ArrayRef<Constant *> NewMembers) {
+  SmallVector<Constant *, 16> Elements;
+  if (InitPrefix) {
+    unsigned NumElements =
+        cast<ArrayType>(InitPrefix->getType())->getNumElements();
+    for (unsigned I = 0; I != NumElements; ++I)
+      Elements.push_back(InitPrefix->getAggregateElement(I));
+  }
+
+  PointerType *VoidPtrTy;
+  Type *EltTy;
+  if (IsOldCtorDtor) {
+    // FIXME: This upgrade is done during linking to support the C API.  See
+    // also IRLinker::linkAppendingVarProto() in IRMover.cpp.
+    VoidPtrTy = Type::getInt8Ty(GV.getContext())->getPointerTo();
+    auto &ST = *cast<StructType>(NewMembers.front()->getType());
+    Type *Tys[3] = {ST.getElementType(0), ST.getElementType(1), VoidPtrTy};
+    EltTy = StructType::get(GV.getContext(), Tys, false);
+  }
+
+  for (auto *V : NewMembers) {
+    Constant *NewV;
+    if (IsOldCtorDtor) {
+      auto *S = cast<ConstantStruct>(V);
+      auto *E1 = mapValue(S->getOperand(0));
+      auto *E2 = mapValue(S->getOperand(1));
+      Value *Null = Constant::getNullValue(VoidPtrTy);
+      NewV =
+          ConstantStruct::get(cast<StructType>(EltTy), E1, E2, Null, nullptr);
+    } else {
+      NewV = cast_or_null<Constant>(mapValue(V));
+    }
+    Elements.push_back(NewV);
+  }
+
+  GV.setInitializer(ConstantArray::get(
+      cast<ArrayType>(GV.getType()->getElementType()), Elements));
+}
+
+void Mapper::scheduleMapGlobalInitializer(GlobalVariable &GV, Constant &Init,
+                                          unsigned MCID) {
+  assert(MCID < MCs.size() && "Invalid mapping context");
+
+  WorklistEntry WE;
+  WE.Kind = WorklistEntry::MapGlobalInit;
+  WE.MCID = MCID;
+  WE.Data.GVInit.GV = &GV;
+  WE.Data.GVInit.Init = &Init;
+  Worklist.push_back(WE);
+}
+
+void Mapper::scheduleMapAppendingVariable(GlobalVariable &GV,
+                                          Constant *InitPrefix,
+                                          bool IsOldCtorDtor,
+                                          ArrayRef<Constant *> NewMembers,
+                                          unsigned MCID) {
+  assert(MCID < MCs.size() && "Invalid mapping context");
+
+  WorklistEntry WE;
+  WE.Kind = WorklistEntry::MapAppendingVar;
+  WE.MCID = MCID;
+  WE.Data.AppendingGV.GV = &GV;
+  WE.Data.AppendingGV.InitPrefix = InitPrefix;
+  WE.AppendingGVIsOldCtorDtor = IsOldCtorDtor;
+  WE.AppendingGVNumNewMembers = NewMembers.size();
+  Worklist.push_back(WE);
+  AppendingInits.append(NewMembers.begin(), NewMembers.end());
+}
+
+void Mapper::scheduleMapGlobalAliasee(GlobalAlias &GA, Constant &Aliasee,
+                                      unsigned MCID) {
+  assert(MCID < MCs.size() && "Invalid mapping context");
+
+  WorklistEntry WE;
+  WE.Kind = WorklistEntry::MapGlobalAliasee;
+  WE.MCID = MCID;
+  WE.Data.GlobalAliasee.GA = &GA;
+  WE.Data.GlobalAliasee.Aliasee = &Aliasee;
+  Worklist.push_back(WE);
+}
+
+void Mapper::scheduleRemapFunction(Function &F, unsigned MCID) {
+  assert(MCID < MCs.size() && "Invalid mapping context");
+
+  WorklistEntry WE;
+  WE.Kind = WorklistEntry::RemapFunction;
+  WE.MCID = MCID;
+  WE.Data.RemapF = &F;
+  Worklist.push_back(WE);
+}
+
+void Mapper::addFlags(RemapFlags Flags) {
+  assert(!hasWorkToDo() && "Expected to have flushed the worklist");
+  this->Flags = this->Flags | Flags;
+}
+
+static Mapper *getAsMapper(void *pImpl) {
+  return reinterpret_cast<Mapper *>(pImpl);
+}
+
+namespace {
+
+class FlushingMapper {
+  Mapper &M;
+
+public:
+  explicit FlushingMapper(void *pImpl) : M(*getAsMapper(pImpl)) {
+    assert(!M.hasWorkToDo() && "Expected to be flushed");
+  }
+  ~FlushingMapper() { M.flush(); }
+  Mapper *operator->() const { return &M; }
+};
+
+} // end namespace
+
+ValueMapper::ValueMapper(ValueToValueMapTy &VM, RemapFlags Flags,
+                         ValueMapTypeRemapper *TypeMapper,
+                         ValueMaterializer *Materializer)
+    : pImpl(new Mapper(VM, Flags, TypeMapper, Materializer)) {}
+
+ValueMapper::~ValueMapper() { delete getAsMapper(pImpl); }
+
+unsigned
+ValueMapper::registerAlternateMappingContext(ValueToValueMapTy &VM,
+                                             ValueMaterializer *Materializer) {
+  return getAsMapper(pImpl)->registerAlternateMappingContext(VM, Materializer);
+}
+
+void ValueMapper::addFlags(RemapFlags Flags) {
+  FlushingMapper(pImpl)->addFlags(Flags);
+}
+
+Value *ValueMapper::mapValue(const Value &V) {
+  return FlushingMapper(pImpl)->mapValue(&V);
+}
+
+Constant *ValueMapper::mapConstant(const Constant &C) {
+  return cast_or_null<Constant>(mapValue(C));
+}
+
+Metadata *ValueMapper::mapMetadata(const Metadata &MD) {
+  return FlushingMapper(pImpl)->mapMetadata(&MD);
+}
+
+MDNode *ValueMapper::mapMDNode(const MDNode &N) {
+  return cast_or_null<MDNode>(mapMetadata(N));
+}
+
+void ValueMapper::remapInstruction(Instruction &I) {
+  FlushingMapper(pImpl)->remapInstruction(&I);
+}
+
+void ValueMapper::remapFunction(Function &F) {
+  FlushingMapper(pImpl)->remapFunction(F);
+}
+
+void ValueMapper::scheduleMapGlobalInitializer(GlobalVariable &GV,
+                                               Constant &Init,
+                                               unsigned MCID) {
+  getAsMapper(pImpl)->scheduleMapGlobalInitializer(GV, Init, MCID);
+}
+
+void ValueMapper::scheduleMapAppendingVariable(GlobalVariable &GV,
+                                               Constant *InitPrefix,
+                                               bool IsOldCtorDtor,
+                                               ArrayRef<Constant *> NewMembers,
+                                               unsigned MCID) {
+  getAsMapper(pImpl)->scheduleMapAppendingVariable(
+      GV, InitPrefix, IsOldCtorDtor, NewMembers, MCID);
+}
+
+void ValueMapper::scheduleMapGlobalAliasee(GlobalAlias &GA, Constant &Aliasee,
+                                           unsigned MCID) {
+  getAsMapper(pImpl)->scheduleMapGlobalAliasee(GA, Aliasee, MCID);
+}
+
+void ValueMapper::scheduleRemapFunction(Function &F, unsigned MCID) {
+  getAsMapper(pImpl)->scheduleRemapFunction(F, MCID);
+}