Revert "Debug Info: Using declarations/DW_TAG_imported_declaration of variables, types, and functions."

This reverts commit r181393 (git 3923d6a87fe7b2c91cc4a7dbd90c4ec7e2316bcd).

This seems to be emitting too much extra debug info for two (known)
reasons:
* full class definitions are emitted when only declarations are expected
* unused using declarations still produce DW_TAG_imported_declarations

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@181947 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CGDebugInfo.cpp b/lib/CodeGen/CGDebugInfo.cpp
index f6ad8f2..2dd1741 100644
--- a/lib/CodeGen/CGDebugInfo.cpp
+++ b/lib/CodeGen/CGDebugInfo.cpp
@@ -2173,30 +2173,6 @@
   return Ty;
 }
 
-llvm::DIDescriptor CGDebugInfo::getDeclarationOrDefinition(const Decl *D) {
-  // We only need a declaration (not a definition) of the type - so use whatever
-  // we would otherwise do to get a type for a pointee. (forward declarations in
-  // limited debug info, full definitions (if the type definition is available)
-  // in unlimited debug info)
-  if (const TypeDecl *TD = dyn_cast<TypeDecl>(D)) {
-    llvm::DIFile DefUnit = getOrCreateFile(TD->getLocation());
-    return CreatePointeeType(CGM.getContext().getTypeDeclType(TD), DefUnit);
-  }
-  // Otherwise fall back to a fairly rudimentary cache of existing declarations.
-  // This doesn't handle providing declarations (for functions or variables) for
-  // entities without definitions in this TU, nor when the definition proceeds
-  // the call to this function.
-  // FIXME: This should be split out into more specific maps with support for
-  // emitting forward declarations and merging definitions with declarations,
-  // the same way as we do for types.
-  llvm::DenseMap<const Decl *, llvm::WeakVH>::iterator I =
-      DeclCache.find(D->getCanonicalDecl());
-  if (I == DeclCache.end())
-    return llvm::DIDescriptor();
-  llvm::Value *V = I->second;
-  return llvm::DIDescriptor(dyn_cast_or_null<llvm::MDNode>(V));
-}
-
 /// getFunctionDeclaration - Return debug info descriptor to describe method
 /// declaration for the given method definition.
 llvm::DISubprogram CGDebugInfo::getFunctionDeclaration(const Decl *D) {
@@ -2368,8 +2344,6 @@
                                getLineNumber(CurLoc), Flags,
                                CGM.getLangOpts().Optimize,
                                Fn, TParamsArray, SPDecl);
-  if (HasDecl)
-    DeclCache.insert(std::make_pair(D->getCanonicalDecl(), llvm::WeakVH(SP)));
 
   // Push function on region stack.
   llvm::MDNode *SPN = SP;
@@ -2980,11 +2954,10 @@
     LinkageName = StringRef();
   llvm::DIDescriptor DContext = 
     getContextDescriptor(dyn_cast<Decl>(D->getDeclContext()));
-  llvm::DIGlobalVariable GV = DBuilder.createStaticVariable(DContext, DeclName, LinkageName,
+  DBuilder.createStaticVariable(DContext, DeclName, LinkageName,
                                 Unit, LineNo, getOrCreateType(T, Unit),
                                 Var->hasInternalLinkage(), Var,
                                 getStaticDataMemberDeclaration(D));
-  DeclCache.insert(std::make_pair(D->getCanonicalDecl(), llvm::WeakVH(GV)));
 }
 
 /// EmitGlobalVariable - Emit information about an objective-c interface.
@@ -3029,38 +3002,22 @@
   // Do not use DIGlobalVariable for enums.
   if (Ty.getTag() == llvm::dwarf::DW_TAG_enumeration_type)
     return;
-  llvm::DIGlobalVariable GV = DBuilder.createStaticVariable(Unit, Name, Name, Unit,
+  DBuilder.createStaticVariable(Unit, Name, Name, Unit,
                                 getLineNumber(VD->getLocation()),
                                 Ty, true, Init,
                                 getStaticDataMemberDeclaration(VD));
-  DeclCache.insert(std::make_pair(VD->getCanonicalDecl(), llvm::WeakVH(GV)));
-}
-
-llvm::DIScope CGDebugInfo::getCurrentContextDescriptor(const Decl *D) {
-  if (!LexicalBlockStack.empty())
-    return llvm::DIScope(LexicalBlockStack.back());
-  return getContextDescriptor(D);
 }
 
 void CGDebugInfo::EmitUsingDirective(const UsingDirectiveDecl &UD) {
+  llvm::DIScope Scope =
+      LexicalBlockStack.empty()
+          ? getContextDescriptor(cast<Decl>(UD.getDeclContext()))
+          : llvm::DIScope(LexicalBlockStack.back());
   DBuilder.createImportedModule(
-      getCurrentContextDescriptor(cast<Decl>(UD.getDeclContext())),
-      getOrCreateNameSpace(UD.getNominatedNamespace()),
+      Scope, getOrCreateNameSpace(UD.getNominatedNamespace()),
       getLineNumber(UD.getLocation()));
 }
 
-void CGDebugInfo::EmitUsingDecl(const UsingDecl &UD) {
-  assert(UD.shadow_size() &&
-         "We shouldn't be codegening an invalid UsingDecl containing no decls");
-  // Emitting one decl is sufficient - debuggers can detect that this is an
-  // overloaded name & provide lookup for all the overloads.
-  const UsingShadowDecl &USD = **UD.shadow_begin();
-  if (llvm::DIDescriptor Target = getDeclarationOrDefinition(USD.getUnderlyingDecl()))
-    DBuilder.createImportedDeclaration(
-        getCurrentContextDescriptor(cast<Decl>(USD.getDeclContext())), Target,
-        getLineNumber(USD.getLocation()));
-}
-
 /// getOrCreateNamesSpace - Return namespace descriptor for the given
 /// namespace decl.
 llvm::DINameSpace 
diff --git a/lib/CodeGen/CGDebugInfo.h b/lib/CodeGen/CGDebugInfo.h
index f221a0c..4080492 100644
--- a/lib/CodeGen/CGDebugInfo.h
+++ b/lib/CodeGen/CGDebugInfo.h
@@ -35,7 +35,6 @@
   class ObjCIvarDecl;
   class ClassTemplateSpecializationDecl;
   class GlobalDecl;
-  class UsingDecl;
 
 namespace CodeGen {
   class CodeGenModule;
@@ -95,9 +94,6 @@
 
   llvm::DenseMap<const char *, llvm::WeakVH> DIFileCache;
   llvm::DenseMap<const FunctionDecl *, llvm::WeakVH> SPCache;
-  /// \brief Cache declarations relevant to DW_TAG_imported_declarations (C++
-  /// using declarations) that aren't covered by other more specific caches.
-  llvm::DenseMap<const Decl *, llvm::WeakVH> DeclCache;
   llvm::DenseMap<const NamespaceDecl *, llvm::WeakVH> NameSpaceCache;
   llvm::DenseMap<const Decl *, llvm::WeakVH> StaticDataMemberCache;
 
@@ -269,9 +265,6 @@
   /// \brief - Emit C++ using directive.
   void EmitUsingDirective(const UsingDirectiveDecl &UD);
 
-  /// \brief - Emit C++ using declaration.
-  void EmitUsingDecl(const UsingDecl &UD);
-
   /// getOrCreateRecordType - Emit record type's standalone debug info. 
   llvm::DIType getOrCreateRecordType(QualType Ty, SourceLocation L);
 
@@ -293,8 +286,6 @@
   /// getContextDescriptor - Get context info for the decl.
   llvm::DIScope getContextDescriptor(const Decl *Decl);
 
-  llvm::DIScope getCurrentContextDescriptor(const Decl *Decl);
-
   /// createRecordFwdDecl - Create a forward decl for a RecordType in a given
   /// context.
   llvm::DIType createRecordFwdDecl(const RecordDecl *, llvm::DIDescriptor);
@@ -338,10 +329,6 @@
   llvm::DIType CreateMemberType(llvm::DIFile Unit, QualType FType,
                                 StringRef Name, uint64_t *Offset);
 
-  /// \brief Retrieve the DIDescriptor, if any, for the canonical form of this
-  /// declaration.
-  llvm::DIDescriptor getDeclarationOrDefinition(const Decl *D);
-
   /// getFunctionDeclaration - Return debug info descriptor to describe method
   /// declaration for the given method definition.
   llvm::DISubprogram getFunctionDeclaration(const Decl *D);
diff --git a/lib/CodeGen/CGDecl.cpp b/lib/CodeGen/CGDecl.cpp
index 41f8409..3ce6dec 100644
--- a/lib/CodeGen/CGDecl.cpp
+++ b/lib/CodeGen/CGDecl.cpp
@@ -72,13 +72,14 @@
   case Decl::Block:
   case Decl::Captured:
   case Decl::ClassScopeFunctionSpecialization:
-  case Decl::UsingShadow:
     llvm_unreachable("Declaration should not be in declstmts!");
   case Decl::Function:  // void X();
   case Decl::Record:    // struct/union/class X;
   case Decl::Enum:      // enum X;
   case Decl::EnumConstant: // enum ? { X = ? }
   case Decl::CXXRecord: // struct/union/class X; [C++]
+  case Decl::Using:          // using X; [C++]
+  case Decl::UsingShadow:
   case Decl::NamespaceAlias:
   case Decl::StaticAssert: // static_assert(X, ""); [C++0x]
   case Decl::Label:        // __label__ x;
@@ -88,10 +89,6 @@
     // None of these decls require codegen support.
     return;
 
-  case Decl::Using:          // using X; [C++]
-    if (CGDebugInfo *DI = getDebugInfo())
-      DI->EmitUsingDecl(cast<UsingDecl>(D));
-    return;
   case Decl::UsingDirective: // using namespace X; [C++]
     if (CGDebugInfo *DI = getDebugInfo())
       DI->EmitUsingDirective(cast<UsingDirectiveDecl>(D));