base: Get bitunions to compile on clang 3.8.

clang was getting very upset and interpretting a member function
pointer as a call to the actual underlying function, and then
complaining that it was a non-static function call without an instance.

It seems what it was really upset about was that the class who's scope
the member function pointer belonged to (the current class) wasn't done
being defined. This *should* be ok as far as I can tell, but clang was
having none of it.

This change reworks how the type of the setter function arguments are
determined to work around that limitation. The bitunion test was run
with clang++ and g++ and both pass, and I've built gem5.opt for ARM
successfully.

Change-Id: Ib9351784a897af4867fe08045577e0247334ea11
Reviewed-on: https://gem5-review.googlesource.com/7581
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>

1 files changed, 19 insertions, 14 deletions

diff --git a/src/base/bitunion.hh b/src/base/bitunion.hh
index 6e7d223d2..38d10dac3 100644
--- a/src/base/bitunion.hh
+++ b/src/base/bitunion.hh
@@ -55,26 +55,31 @@ class BitfieldTypeImpl : public Base
                   "Bitfield base class must be empty.");
 
   private:
-    using Base::setter;
 
-    template<typename T>
-    struct TypeDeducer;
+    struct TypeDeducer
+    {
+        template<typename>
+        struct T;
 
-    template<typename T>
-    friend class TypeDeducer;
+        template<typename C, typename Type1, typename Type2>
+        struct T<void (C::*)(Type1 &, Type2)>
+        {
+            typedef Type1 Storage;
+            typedef Type2 Type;
+        };
 
-    template<typename Type1, typename Type2>
-    struct TypeDeducer<void (Base::*)(Type1 &, Type2)>
-    {
-        typedef Type1 Storage;
-        typedef Type2 Type;
+        struct Wrapper : public Base
+        {
+            using Base::setter;
+        };
+
+        typedef typename T<decltype(&Wrapper::setter)>::Storage Storage;
+        typedef typename T<decltype(&Wrapper::setter)>::Type Type;
     };
 
   protected:
-    typedef typename TypeDeducer<
-            decltype(&BitfieldTypeImpl<Base>::setter)>::Storage Storage;
-    typedef typename TypeDeducer<
-            decltype(&BitfieldTypeImpl<Base>::setter)>::Type Type;
+    typedef typename TypeDeducer::Storage Storage;
+    typedef typename TypeDeducer::Type Type;
 
     Type getter(const Storage &storage) const = delete;
     void setter(Storage &storage, Type val) = delete;