DR1359: A constexpr constructor does not need to initialize an empty struct or

empty union. This still rejects anonymous member structs or unions which only
contain such empty class types, pending standard wording defining exactly what
an empty class type is.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@150157 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Sema/SemaDeclCXX.cpp b/lib/Sema/SemaDeclCXX.cpp
index 62332b8b4aaac73a20c5af3f507279539dad85a4..8ba84fe86a50d8b82e45c2e29850cc41f899c966 100644 (file)
--- a/lib/Sema/SemaDeclCXX.cpp
+++ b/lib/Sema/SemaDeclCXX.cpp
@@ -815,7 +815,11 @@ static void CheckConstexprCtorInitializer(Sema &SemaRef,
                                           bool &Diagnosed) {
   if (Field->isUnnamedBitfield())
     return;
-  
+
+  if (Field->isAnonymousStructOrUnion() &&
+      Field->getType()->getAsCXXRecordDecl()->isEmpty())
+    return;
+
   if (!Inits.count(Field)) {
     if (!Diagnosed) {
       SemaRef.Diag(Dcl->getLocation(), diag::err_constexpr_ctor_missing_init);
@@ -901,11 +905,14 @@ bool Sema::CheckConstexprFunctionBody(const FunctionDecl *Dcl, Stmt *Body,
   if (const CXXConstructorDecl *Constructor
         = dyn_cast<CXXConstructorDecl>(Dcl)) {
     const CXXRecordDecl *RD = Constructor->getParent();
-    // - every non-static data member and base class sub-object shall be
-    //   initialized;
+    // DR1359:
+    // - every non-variant non-static data member and base class sub-object
+    //   shall be initialized;
+    // - if the class is a non-empty union, or for each non-empty anonymous
+    //   union member of a non-union class, exactly one non-static data member
+    //   shall be initialized;
     if (RD->isUnion()) {
-      // DR1359: Exactly one member of a union shall be initialized.
-      if (Constructor->getNumCtorInitializers() == 0) {
+      if (Constructor->getNumCtorInitializers() == 0 && !RD->isEmpty()) {
         Diag(Dcl->getLocation(), diag::err_constexpr_union_ctor_no_init);
         return false;
       }

diff --git a/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p4.cpp b/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p4.cpp
index abd5292ada7187ede6b132002304118853950efd..86b7ded95950fed2194c84bbdb073e5c204ed624 100644 (file)
--- a/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p4.cpp
+++ b/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p4.cpp
@@ -151,6 +151,16 @@ struct AnonMembers {
   constexpr AnonMembers(int(&)[6]) {} // expected-error {{constexpr constructor must initialize all members}}
 };
 
+union Empty {
+  constexpr Empty() {} // ok
+} constexpr empty1;
+
+struct EmptyVariant {
+  union {};
+  struct {};
+  constexpr EmptyVariant() {} // ok
+} constexpr empty2;
+
 template<typename T> using Int = int;
 template<typename T>
 struct TemplateInit {