[OPENMP] Fix PR38823: Do not emit vtable if it is not used in target

context.

If the explicit template instantiation definition defined outside of the
target context, its vtable should not be marked as used. This is true
for other situations where the compiler want to emit vtables
unconditionally.

llvm-svn: 341570

clang/lib/Sema/SemaDeclCXX.cpp

@@ -14903,6 +14903,11 @@ void Sema::MarkVTableUsed(SourceLocation Loc, CXXRecordDecl *Class,
   if (!Class->isDynamicClass() || Class->isDependentContext() ||
       CurContext->isDependentContext() || isUnevaluatedContext())
     return;
+  // Do not mark as used if compiling for the device outside of the target
+  // region.
+  if (LangOpts.OpenMP && LangOpts.OpenMPIsDevice &&
+      !isInOpenMPDeclareTargetContext() && !getCurFunctionDecl())
+    return;
 
   // Try to insert this class into the map.
   LoadExternalVTableUses();

clang/test/OpenMP/declare_target_codegen.cpp

@@ -12,7 +12,8 @@
 
 // SIMD-ONLY-NOT: {{__kmpc|__tgt}}
 
-// CHECK-NOT: define {{.*}}{{baz1|baz4|maini1}}
+// CHECK-NOT: define {{.*}}{{baz1|baz4|maini1|Base}}
+// CHECK-DAG: Bake
 // CHECK-NOT: @{{hhh|ggg|fff|eee}} =
 // CHECK-DAG: @aaa = external global i32,
 // CHECK-DAG: @bbb = global i32 0,
@@ -140,9 +141,25 @@ int baz5() {
   return a;
 }
 
+template <typename T>
+struct Base {
+  virtual ~Base() {}
+};
+
+template class Base<int>;
+
+template <typename T>
+struct Bake {
+  virtual ~Bake() {}
+};
+
+#pragma omp declare target
+template class Bake<int>;
+#pragma omp end declare target
+
 // CHECK-DAG: declare extern_weak signext i32 @__create()
 
-// CHECK-NOT: define {{.*}}{{baz1|baz4|maini1}}
+// CHECK-NOT: define {{.*}}{{baz1|baz4|maini1|Base}}
 
 // CHECK-DAG: !{i32 1, !"aaa", i32 0, i32 {{[0-9]+}}}
 // CHECK-DAG: !{i32 1, !"ccc", i32 0, i32 {{[0-9]+}}}