commit 30ecfad3af057bff74d1c98099eda0677525574e
author Richard Smith <richard-llvm@metafoo.co.uk> Thu Feb 09 06:40:58 2012 +0000
committer Richard Smith <richard-llvm@metafoo.co.uk> Thu Feb 09 06:40:58 2012 +0000
tree 5a8c3f5a0718e3c0f236529fed67a4ed8c5b2420
parent ff3b9fdbfd4ff3a8361640c0d8a12d9f0cc1ce6f

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

lib/Sema/SemaDeclCXX.cpp

diff --git a/lib/Sema/SemaDeclCXX.cpp b/lib/Sema/SemaDeclCXX.cpp
index 62332b8..8ba84fe 100644
--- a/lib/Sema/SemaDeclCXX.cpp
+++ b/lib/Sema/SemaDeclCXX.cpp
@@ -815,7 +815,11 @@
                                           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 @@
   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;
       }

test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p4.cpp

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 abd5292..86b7ded 100644
--- 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 @@
   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 {