compiler: Avoid crashes on erroneous input.

From-SVN: r184274

gcc/go/gofrontend/backend.h

@@ -126,7 +126,9 @@ class Backend
 
   // Fill in a placeholder pointer type as a pointer.  This takes a
   // type returned by placeholder_pointer_type and arranges for it to
-  // point to to_type.  Returns true on success, false on failure.
+  // point to the type that TO_TYPE points to (that is, PLACEHOLDER
+  // becomes the same type as TO_TYPE).  Returns true on success,
+  // false on failure.
   virtual bool
   set_placeholder_pointer_type(Btype* placeholder, Btype* to_type) = 0;
 

gcc/go/gofrontend/gogo.cc

@@ -4180,6 +4180,11 @@ Variable::get_backend_variable(Gogo* gogo, Named_object* function,
 					    package != NULL,
 					    Gogo::is_hidden_name(name),
 					    this->location_);
+	  else if (function == NULL)
+	    {
+	      go_assert(saw_errors());
+	      bvar = backend->error_variable();
+	    }
 	  else
 	    {
 	      tree fndecl = function->func_value()->get_decl();

gcc/go/gofrontend/types.cc

@@ -3595,7 +3595,7 @@ Pointer_type::do_hash_for_method(Gogo* gogo) const
   return this->to_type_->hash_for_method(gogo) << 4;
 }
 
-// The tree for a pointer type.
+// Get the backend representation for a pointer type.
 
 Btype*
 Pointer_type::do_get_backend(Gogo* gogo)
@@ -5345,6 +5345,7 @@ Array_type::do_get_backend(Gogo* gogo)
 }
 
 // Return the backend representation of the element type.
+
 Btype*
 Array_type::get_backend_element(Gogo* gogo)
 {
@@ -7567,6 +7568,11 @@ Find_type_use::type(Type* type)
 	  this->find_type_->add_dependency(type->named_type());
 	  break;
 
+	case Type::TYPE_NAMED:
+	case Type::TYPE_FORWARD:
+	  go_assert(saw_errors());
+	  break;
+
 	case Type::TYPE_VOID:
 	case Type::TYPE_SINK:
 	case Type::TYPE_FUNCTION:
@@ -7575,8 +7581,6 @@ Find_type_use::type(Type* type)
 	case Type::TYPE_MAP:
 	case Type::TYPE_CHANNEL:
 	case Type::TYPE_INTERFACE:
-	case Type::TYPE_NAMED:
-	case Type::TYPE_FORWARD:
 	default:
 	  go_unreachable();
 	}