[CXX] Templates specialization visibility can be wrong

Summary:
Under some conditions, LinkageComputer can get the visibility for
ClassTemplateSpecializationDecl wrong because it failed to find the Decl
that has the explicit visibility.

This fixes:
llvm.org/bugs/pr36810
rdar://problem/38080953

Reviewers: rsmith, arphaman, doug.gregor

Reviewed By: doug.gregor

Subscribers: doug.gregor, cfe-commits

Differential Revision: https://reviews.llvm.org/D44670

llvm-svn: 330338

Author: cachemeifyoucan

clang/lib/AST/Decl.cpp

@@ -1092,9 +1092,18 @@ getExplicitVisibilityAux(const NamedDecl *ND,
   // If there wasn't explicit visibility there, and this is a
   // specialization of a class template, check for visibility
   // on the pattern.
-  if (const auto *spec = dyn_cast<ClassTemplateSpecializationDecl>(ND))
-    return getVisibilityOf(spec->getSpecializedTemplate()->getTemplatedDecl(),
-                           kind);
+  if (const auto *spec = dyn_cast<ClassTemplateSpecializationDecl>(ND)) {
+    // Walk all the template decl till this point to see if there are
+    // explicit visibility attributes.
+    const auto *TD = spec->getSpecializedTemplate()->getTemplatedDecl();
+    while (TD != nullptr) {
+      auto Vis = getVisibilityOf(TD, kind);
+      if (Vis != None)
+        return Vis;
+      TD = TD->getPreviousDecl();
+    }
+    return None;
+  }
 
   // Use the most recent declaration.
   if (!IsMostRecent && !isa<NamespaceDecl>(ND)) {

clang/test/CodeGenCXX/visibility-pr36810.cpp

@@ -0,0 +1,23 @@
+// RUN: %clang_cc1 -triple x86_64-apple-macosx -std=c++11 -fvisibility hidden -emit-llvm -o - %s -O2 -disable-llvm-passes | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx -DUNDEF_G -std=c++11 -fvisibility hidden -emit-llvm -o - %s -O2 -disable-llvm-passes | FileCheck %s
+
+namespace std {
+template <class>
+class __attribute__((__type_visibility__("default"))) shared_ptr {
+  template <class> friend class shared_ptr;
+};
+}
+struct dict;
+#ifndef UNDEF_G
+std::shared_ptr<dict> g;
+#endif
+class __attribute__((visibility("default"))) Bar;
+template <class = std::shared_ptr<Bar>>
+class __attribute__((visibility("default"))) i {
+  std::shared_ptr<int> foo() const;
+};
+
+// CHECK: define void @_ZNK1iISt10shared_ptrI3BarEE3fooEv
+template <> std::shared_ptr<int> i<>::foo() const {
+  return std::shared_ptr<int>();
+}