Replace Sema's map of locally-scoped extern "C" declarations with a DeclContext

of extern "C" declarations. This is simpler and vastly more efficient for
modules builds (we no longer need to load *all* extern "C" declarations to
determine if we have a redeclaration).

No functionality change intended.

llvm-svn: 231538

3 files changed, 9 insertions, 24 deletions

diff --git a/clang/lib/Sema/MultiplexExternalSemaSource.cpp b/clang/lib/Sema/MultiplexExternalSemaSource.cpp
index a0315777675..194c3693c1d 100644
--- a/clang/lib/Sema/MultiplexExternalSemaSource.cpp
+++ b/clang/lib/Sema/MultiplexExternalSemaSource.cpp
@@ -242,12 +242,6 @@ void MultiplexExternalSemaSource::ReadUnusedLocalTypedefNameCandidates(
     Sources[i]->ReadUnusedLocalTypedefNameCandidates(Decls);
 }
 
-void MultiplexExternalSemaSource::ReadLocallyScopedExternCDecls(
-                                           SmallVectorImpl<NamedDecl*> &Decls) {
-  for(size_t i = 0; i < Sources.size(); ++i)
-    Sources[i]->ReadLocallyScopedExternCDecls(Decls);
-}
-
 void MultiplexExternalSemaSource::ReadReferencedSelectors(
                   SmallVectorImpl<std::pair<Selector, SourceLocation> > &Sels) {
   for(size_t i = 0; i < Sources.size(); ++i)
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 462854417e1..778b617628e 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -4864,27 +4864,13 @@ Sema::RegisterLocallyScopedExternCDecl(NamedDecl *ND, Scope *S) {
     return;
 
   // Note that we have a locally-scoped external with this name.
-  // FIXME: There can be multiple such declarations if they are functions marked
-  // __attribute__((overloadable)) declared in function scope in C.
-  LocallyScopedExternCDecls[ND->getDeclName()] = ND;
+  Context.getExternCContextDecl()->makeDeclVisibleInContext(ND);
 }
 
 NamedDecl *Sema::findLocallyScopedExternCDecl(DeclarationName Name) {
-  if (ExternalSource) {
-    // Load locally-scoped external decls from the external source.
-    // FIXME: This is inefficient. Maybe add a DeclContext for extern "C" decls?
-    SmallVector<NamedDecl *, 4> Decls;
-    ExternalSource->ReadLocallyScopedExternCDecls(Decls);
-    for (unsigned I = 0, N = Decls.size(); I != N; ++I) {
-      llvm::DenseMap<DeclarationName, NamedDecl *>::iterator Pos
-        = LocallyScopedExternCDecls.find(Decls[I]->getDeclName());
-      if (Pos == LocallyScopedExternCDecls.end())
-        LocallyScopedExternCDecls[Decls[I]->getDeclName()] = Decls[I];
-    }
-  }
-
-  NamedDecl *D = LocallyScopedExternCDecls.lookup(Name);
-  return D ? D->getMostRecentDecl() : nullptr;
+  // FIXME: We can have multiple results via __attribute__((overloadable)).
+  auto Result = Context.getExternCContextDecl()->lookup(Name);
+  return Result.empty() ? nullptr : *Result.begin();
 }
 
 /// \brief Diagnose function specifiers on a declaration of an identifier that
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 1df0701ee9f..6936539f1ca 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -289,6 +289,11 @@ TemplateDeclInstantiator::VisitTranslationUnitDecl(TranslationUnitDecl *D) {
 }
 
 Decl *
+TemplateDeclInstantiator::VisitExternCContextDecl(ExternCContextDecl *D) {
+  llvm_unreachable("extern \"C\" context cannot be instantiated");
+}
+
+Decl *
 TemplateDeclInstantiator::VisitLabelDecl(LabelDecl *D) {
   LabelDecl *Inst = LabelDecl::Create(SemaRef.Context, Owner, D->getLocation(),
                                       D->getIdentifier());