Update to LLVM's use of TrackingWeakVH; NFC

[sanjoy]

Summary

Depends on D32266

[davide]

Thank you very much for fixing the regression with this patchset!

lib/CodeGen/CGDeclCXX.cpp

if (ExitBlock) {
       Builder.CreateBr(ExitBlock);
       EmitBlock(ExitBlock);
     }
   }
 
   FinishFunction();
 }
 
-void CodeGenFunction::GenerateCXXGlobalDtorsFunc(llvm::Function *Fn,
-                  const std::vector<std::pair<llvm::WeakVH, llvm::Constant*> >
-                                                &DtorsAndObjects) {
+void CodeGenFunction::GenerateCXXGlobalDtorsFunc(
+    llvm::Function *Fn,
+    const std::vector<std::pair<llvm::WeakTrackingVH, llvm::Constant *>>
   {
     auto NL = ApplyDebugLocation::CreateEmpty(*this);
     StartFunction(GlobalDecl(), getContext().VoidTy, Fn,
                   getTypes().arrangeNullaryFunction(), FunctionArgList());
     // Emit an artificial location for this function.
     auto AL = ApplyDebugLocation::CreateArtificial(*this);
 
     // Emit the dtors, in reverse order from construction.

lib/CodeGen/CGObjCMac.cpp

protected:
   /// DefinedCategories - List of defined categories.
   SmallVector<llvm::GlobalValue*, 16> DefinedCategories;
 
   /// DefinedNonLazyCategories - List of defined "non-lazy" categories.
   SmallVector<llvm::GlobalValue*, 16> DefinedNonLazyCategories;
 
   /// Cached reference to the class for constant strings. This value has type
   /// int * but is actually an Obj-C class pointer.
-  llvm::WeakVH ConstantStringClassRef;
+  llvm::WeakTrackingVH ConstantStringClassRef;
 
   /// \brief The LLVM type corresponding to NSConstantString.
   llvm::StructType *NSConstantStringType = nullptr;
 
   llvm::StringMap<llvm::GlobalVariable *> NSConstantStringMap;
 
   /// GetNameForMethod - Return a name for the given method.
   /// \param[out] NameOut - The return value.

lib/CodeGen/CodeGenFunction.h

public:
   /// GenerateCXXGlobalInitFunc - Generates code for initializing global
   /// variables.
   void GenerateCXXGlobalInitFunc(llvm::Function *Fn,
                                  ArrayRef<llvm::Function *> CXXThreadLocals,
                                  Address Guard = Address::invalid());
 
   /// GenerateCXXGlobalDtorsFunc - Generates code for destroying global
   /// variables.
-  void GenerateCXXGlobalDtorsFunc(llvm::Function *Fn,
-                                  const std::vector<std::pair<llvm::WeakVH,
-                                  llvm::Constant*> > &DtorsAndObjects);
+  void GenerateCXXGlobalDtorsFunc(
+      llvm::Function *Fn,
+      const std::vector<std::pair<llvm::WeakTrackingVH, llvm::Constant *>>
+          &DtorsAndObjects);
 
   void GenerateCXXGlobalVarDeclInitFunc(llvm::Function *Fn,
                                         const VarDecl *D,
                                         llvm::GlobalVariable *Addr,
                                         bool PerformInit);
 
   void EmitCXXConstructExpr(const CXXConstructExpr *E, AggValueSlot Dest);
   

lib/CodeGen/CodeGenModule.h

private:
   llvm::DenseSet<GlobalDecl> DiagnosedConflictingDefinitions;
 
   /// A queue of (optional) vtables to consider emitting.
   std::vector<const CXXRecordDecl*> DeferredVTables;
 
   /// List of global values which are required to be present in the object file;
   /// bitcast to i8*. This is used for forcing visibility of symbols which may
   /// otherwise be optimized out.
-  std::vector<llvm::WeakVH> LLVMUsed;
-  std::vector<llvm::WeakVH> LLVMCompilerUsed;
+  std::vector<llvm::WeakTrackingVH> LLVMUsed;
+  std::vector<llvm::WeakTrackingVH> LLVMCompilerUsed;
 
   /// Store the list of global constructors and their respective priorities to
   /// be emitted when the translation unit is complete.
   CtorList GlobalCtors;
 
   /// Store the list of global destructors and their respective priorities to be
   /// emitted when the translation unit is complete.
   CtorList GlobalDtors;
struct GlobalInitPriorityCmp {
     }
   };
 
   /// Global variables with initializers whose order of initialization is set by
   /// init_priority attribute.
   SmallVector<GlobalInitData, 8> PrioritizedCXXGlobalInits;
 
   /// Global destructor functions and arguments that need to run on termination.
-  std::vector<std::pair<llvm::WeakVH,llvm::Constant*> > CXXGlobalDtors;
+  std::vector<std::pair<llvm::WeakTrackingVH, llvm::Constant *>> CXXGlobalDtors;
 
   /// \brief The complete set of modules that has been imported.
   llvm::SetVector<clang::Module *> ImportedModules;
 
   /// \brief The set of modules for which the module initializers
   /// have been emitted.
   llvm::SmallPtrSet<clang::Module *, 16> EmittedModuleInitializers;
 
   /// \brief A vector of metadata strings.
   SmallVector<llvm::Metadata *, 16> LinkerOptionsMetadata;
 
   /// @name Cache for Objective-C runtime types
   /// @{
 
   /// Cached reference to the class for constant strings. This value has type
   /// int * but is actually an Obj-C class pointer.
-  llvm::WeakVH CFConstantStringClassRef;
+  llvm::WeakTrackingVH CFConstantStringClassRef;
 
   /// \brief The type used to describe the state of a fast enumeration in
   /// Objective-C's for..in loop.
   QualType ObjCFastEnumerationStateType;
   
   /// @}
 
   /// Lazily create the Objective-C runtime

lib/CodeGen/CodeGenModule.cpp

 
 void CodeGenModule::addCompilerUsedGlobal(llvm::GlobalValue *GV) {
   assert(!GV->isDeclaration() &&
          "Only globals with definition can force usage.");
   LLVMCompilerUsed.emplace_back(GV);
 }
 
 static void emitUsed(CodeGenModule &CGM, StringRef Name,
-                     std::vector<llvm::WeakVH> &List) {
+                     std::vector<llvm::WeakTrackingVH> &List) {
   // Don't create llvm.used if there is no need.
   if (List.empty())
     return;
 
   // Convert List to what ConstantArray needs.
   SmallVector<llvm::Constant*, 8> UsedArray;
   UsedArray.resize(List.size());
   for (unsigned i = 0, e = List.size(); i != e; ++i) {