r206929 - PR18746: If a constexpr function has a dependent return type and no return

[Richard Smith]

Author: rsmith
Date: Tue Apr 22 18:14:23 2014
New Revision: 206929

URL: http://llvm.org/viewvc/llvm-project?rev=206929&view=rev
Log:
PR18746: If a constexpr function has a dependent return type and no return
statements, don't diagnose; the return type might end up being 'void'.

Patch by Rahul Jain! Tiny tweaks by me.

Modified:
    cfe/trunk/lib/Sema/SemaDeclCXX.cpp
    cfe/trunk/test/SemaCXX/cxx1y-deduced-return-type.cpp

Modified: cfe/trunk/lib/Sema/SemaDeclCXX.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDeclCXX.cpp?rev=206929&r1=206928&r2=206929&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaDeclCXX.cpp (original)
+++ cfe/trunk/lib/Sema/SemaDeclCXX.cpp Tue Apr 22 18:14:23 2014
@@ -1175,10 +1175,12 @@ bool Sema::CheckConstexprFunctionBody(co
   } else {
     if (ReturnStmts.empty()) {
       // C++1y doesn't require constexpr functions to contain a 'return'
-      // statement. We still do, unless the return type is void, because
+      // statement. We still do, unless the return type might be void, because
       // otherwise if there's no return statement, the function cannot
       // be used in a core constant expression.
-      bool OK = getLangOpts().CPlusPlus1y && Dcl->getReturnType()->isVoidType();
+      bool OK = getLangOpts().CPlusPlus1y &&
+                (Dcl->getReturnType()->isVoidType() ||
+                 Dcl->getReturnType()->isDependentType());
       Diag(Dcl->getLocation(),
            OK ? diag::warn_cxx11_compat_constexpr_body_no_return
               : diag::err_constexpr_body_no_return);

Modified: cfe/trunk/test/SemaCXX/cxx1y-deduced-return-type.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/cxx1y-deduced-return-type.cpp?rev=206929&r1=206928&r2=206929&view=diff
==============================================================================
--- cfe/trunk/test/SemaCXX/cxx1y-deduced-return-type.cpp (original)
+++ cfe/trunk/test/SemaCXX/cxx1y-deduced-return-type.cpp Tue Apr 22 18:14:23 2014
@@ -261,6 +261,13 @@ namespace DefaultedMethods {
 
 namespace Constexpr {
   constexpr auto f1(int n) { return n; }
+  template<typename T> struct X { constexpr auto f() {} }; // PR18746
+  template<typename T> struct Y { constexpr T f() {} }; // expected-note {{control reached end of constexpr function}}
+  void f() {
+    X<int>().f();
+    Y<void>().f();
+    constexpr int q = Y<int>().f(); // expected-error {{must be initialized by a constant expression}} expected-note {{in call to '&Y<int>()->f()'}}
+  }
   struct NonLiteral { ~NonLiteral(); } nl; // expected-note {{user-provided destructor}}
   constexpr auto f2(int n) { return nl; } // expected-error {{return type 'Constexpr::NonLiteral' is not a literal type}}
 }