Provide the correct mangling and linkage for certain unnamed nested classes.

This corrects the mangling and linkage of classes (& their member functions) in
cases like this:

  struct foo {
    struct {
      void func() { ... }
    } x;
  };

we were accidentally giving this nested unnamed struct 'no' linkage where it
should've had the linkage of the outer class. The mangling was incorrecty too,
mangling as TU-wide unnamed type mangling of $_X rather than class-scoped
mangling of UtX_.

This also fixes -Wunused-member-function which would incorrectly diagnose
'func' as unused due to it having no linkage & thus appearing to be TU-local
when in fact it might be correctly used in another TU.

Similar mangling should be applied to function local classes in similar cases
but I've deferred that for a subsequent patch.

Review/discussion by Richard Smith, John McCall, & especially Eli Friedman.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@167906 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 17 insertions, 0 deletions

diff --git a/lib/AST/ASTContext.cpp b/lib/AST/ASTContext.cpp
index 577dd0adaf..80ce66a017 100644
--- a/lib/AST/ASTContext.cpp
+++ b/lib/AST/ASTContext.cpp
@@ -7508,6 +7508,23 @@ size_t ASTContext::getSideTableAllocatedMemory() const {
     + llvm::capacity_in_bytes(ClassScopeSpecializationPattern);
 }
 
+void ASTContext::addUnnamedTag(const TagDecl *Tag) {
+  // FIXME: This mangling should be applied to function local classes too
+  if (!Tag->getName().empty() || Tag->getTypedefNameForAnonDecl() ||
+      !isa<CXXRecordDecl>(Tag->getParent()) || Tag->getLinkage() != ExternalLinkage)
+    return;
+
+  std::pair<llvm::DenseMap<const DeclContext *, unsigned>::iterator, bool> P =
+    UnnamedMangleContexts.insert(std::make_pair(Tag->getParent(), 0));
+  UnnamedMangleNumbers.insert(std::make_pair(Tag, P.first->second++));
+}
+
+int ASTContext::getUnnamedTagManglingNumber(const TagDecl *Tag) const {
+  llvm::DenseMap<const TagDecl *, unsigned>::const_iterator I =
+    UnnamedMangleNumbers.find(Tag);
+  return I != UnnamedMangleNumbers.end() ? I->second : -1;
+}
+
 unsigned ASTContext::getLambdaManglingNumber(CXXMethodDecl *CallOperator) {
   CXXRecordDecl *Lambda = CallOperator->getParent();
   return LambdaMangleContexts[Lambda->getDeclContext()]