compiler: Function_type and Backend_function_type should not be identical

    
    Function_type and Backend_function_type have different backend
    representations, so they should not be identical. Otherwise it
    confuses Type::type_btypes map.
    
    Reviewed-on: https://go-review.googlesource.com/90975

From-SVN: r257216

gcc/go/gofrontend/MERGE

-bbce8a9af264b25c5f70bafb2ce95d4fed158d68
+a347356d0f432cafb69f0cc5833d27663736a042
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/types.cc

@@ -4442,6 +4442,9 @@ Function_type::is_identical(const Function_type* t, bool ignore_receiver,
 			    Cmp_tags cmp_tags, bool errors_are_identical,
 			    std::string* reason) const
 {
+  if (this->is_backend_function_type() != t->is_backend_function_type())
+    return false;
+
   if (!ignore_receiver)
     {
       const Typed_identifier* r1 = this->receiver();

gcc/go/gofrontend/types.h

@@ -2074,6 +2074,11 @@ class Function_type : public Type
   Btype*
   get_backend_fntype(Gogo*);
 
+  // Return whether this is a Backend_function_type.
+  virtual bool
+  is_backend_function_type() const
+  { return false; }
+
  protected:
   int
   do_traverse(Traverse*);
@@ -2167,6 +2172,12 @@ class Backend_function_type : public Function_type
       : Function_type(receiver, parameters, results, location)
   { }
 
+  // Return whether this is a Backend_function_type. This overrides
+  // Function_type::is_backend_function_type.
+  bool
+  is_backend_function_type() const
+  { return true; }
+
  protected:
   Btype*
   do_get_backend(Gogo* gogo)