[clang codegen] Add dso_local/hidden/etc. markings to VTT declarations

We were marking definitions, but not declarations. Marking declarations
makes computing the address more efficient.

Fixes issue reported at https://discourse.llvm.org/t/63090

Differential Revision: https://reviews.llvm.org/D128482

clang/lib/CodeGen/CGVTT.cpp

@@ -96,9 +96,6 @@ CodeGenVTables::EmitVTTDefinition(llvm::GlobalVariable *VTT,
 
   if (CGM.supportsCOMDAT() && VTT->isWeakForLinker())
     VTT->setComdat(CGM.getModule().getOrInsertComdat(VTT->getName()));
-
-  // Set the right visibility.
-  CGM.setGVProperties(VTT, RD);
 }
 
 llvm::GlobalVariable *CodeGenVTables::GetAddrOfVTT(const CXXRecordDecl *RD) {
@@ -122,6 +119,7 @@ llvm::GlobalVariable *CodeGenVTables::GetAddrOfVTT(const CXXRecordDecl *RD) {
   llvm::GlobalVariable *GV = CGM.CreateOrReplaceCXXRuntimeVariable(
       Name, ArrayType, llvm::GlobalValue::ExternalLinkage, Align);
   GV->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
+  CGM.setGVProperties(GV, RD);
   return GV;
 }
 

clang/test/CodeGenCXX/visibility.cpp

@@ -118,6 +118,8 @@ namespace test48 {
 // CHECK-HIDDEN: @_ZN6Test143varE = external global
 // CHECK: @_ZN6Test154TempINS_1AEE5Inner6bufferE = external global [0 x i8]
 // CHECK-HIDDEN: @_ZN6Test154TempINS_1AEE5Inner6bufferE = external global [0 x i8]
+// CHECK: @_ZTVN6test701BE = external hidden unnamed_addr constant { [5 x ptr] }, align 8
+// CHECK: @_ZTTN6test701BE = external hidden unnamed_addr constant [2 x ptr], align 8
 
 namespace test27 {
   template<typename T>
@@ -1317,3 +1319,16 @@ namespace test69 {
   // CHECK-LABEL: define void @_ZN6test693foo1fEv
   // CHECK-HIDDEN-LABEL: define hidden void @_ZN6test693foo1fEv
 }
+
+namespace test70 {
+  // Make sure both the vtable and VTT declarations are marked "hidden"
+  class HIDDEN A {
+    virtual void a();
+  };
+  class HIDDEN B : virtual A {
+    void a() override;
+    ~B();
+  };
+  B::~B() {}
+  // Check lines at top of file.
+}