[RFA v2 3/3] Use an enum to represent subclasses of symbol

[Tom Tromey <tom@tromey.com>]

This changes struct symbol to use an enum to encode the concrete
subclass of a particular symbol.  Note that "enum class" doesn't work
properly with bitfields, so a plain enum is used.

2017-11-17  Tom Tromey  <tom@tromey.com>

	* symtab.h (enum symbol_subclass_kind): New.
	(struct symbol) <is_cplus_template_function, is_rust_vtable>:
	Remove.
	<subclass>: New member.
	(SYMBOL_IS_CPLUS_TEMPLATE_FUNCTION): Update.
	* rust-lang.c (rust_get_trait_object_pointer): Update.
	* dwarf2read.c (read_func_scope): Update.
	(read_variable): Update.
---
 gdb/ChangeLog    | 11 +++++++++++
 gdb/dwarf2read.c |  4 ++--
 gdb/rust-lang.c  |  2 +-
 gdb/symtab.h     | 26 ++++++++++++++++++--------
 4 files changed, 32 insertions(+), 11 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 1551654..1502f06 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,16 @@
 2017-11-17  Tom Tromey  <tom@tromey.com>
 
+	* symtab.h (enum symbol_subclass_kind): New.
+	(struct symbol) <is_cplus_template_function, is_rust_vtable>:
+	Remove.
+	<subclass>: New member.
+	(SYMBOL_IS_CPLUS_TEMPLATE_FUNCTION): Update.
+	* rust-lang.c (rust_get_trait_object_pointer): Update.
+	* dwarf2read.c (read_func_scope): Update.
+	(read_variable): Update.
+
+2017-11-17  Tom Tromey  <tom@tromey.com>
+
 	* dwarf2read.c (read_func_scope): Update.
 	* symtab.h (struct template_symbol): Derive from symbol.
 	<base>: Remove.
diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index 86b6996..5437d21 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -12263,7 +12263,7 @@ read_func_scope (struct die_info *die, struct dwarf2_cu *cu)
 	  || child_die->tag == DW_TAG_template_value_param)
 	{
 	  templ_func = allocate_template_symbol (objfile);
-	  templ_func->is_cplus_template_function = 1;
+	  templ_func->subclass = SYMBOL_TEMPLATE;
 	  break;
 	}
     }
@@ -12821,7 +12821,7 @@ read_variable (struct die_info *die, struct dwarf2_cu *cu)
 				    struct rust_vtable_symbol);
 	  initialize_objfile_symbol (storage);
 	  storage->concrete_type = containing_type;
-	  storage->is_rust_vtable = 1;
+	  storage->subclass = SYMBOL_RUST_VTABLE;
 	}
     }
 
diff --git a/gdb/rust-lang.c b/gdb/rust-lang.c
index 832f77f..f3562e0 100644
--- a/gdb/rust-lang.c
+++ b/gdb/rust-lang.c
@@ -421,7 +421,7 @@ rust_get_trait_object_pointer (struct value *value)
 
   CORE_ADDR vtable = value_as_address (value_field (value, vtable_field));
   struct symbol *symbol = find_symbol_at_address (vtable);
-  if (symbol == NULL || !symbol->is_rust_vtable)
+  if (symbol == NULL || symbol->subclass != SYMBOL_RUST_VTABLE)
     return NULL;
 
   struct rust_vtable_symbol *vtable_sym
diff --git a/gdb/symtab.h b/gdb/symtab.h
index 6ecce81..ad8d602 100644
--- a/gdb/symtab.h
+++ b/gdb/symtab.h
@@ -1008,6 +1008,21 @@ struct symbol_impl
   const struct symbol_register_ops *ops_register;
 };
 
+/* struct symbol has some subclasses.  This enum is used to
+   differentiate between them.  */
+
+enum symbol_subclass_kind
+{
+  /* Plain struct symbol.  */
+  SYMBOL_NONE,
+
+  /* struct template_symbol.  */
+  SYMBOL_TEMPLATE,
+
+  /* struct rust_vtable_symbol.  */
+  SYMBOL_RUST_VTABLE
+};
+
 /* This structure is space critical.  See space comments at the top.  */
 
 struct symbol
@@ -1057,14 +1072,9 @@ struct symbol
   /* Whether this is an inlined function (class LOC_BLOCK only).  */
   unsigned is_inlined : 1;
 
-  /* True if this is a C++ function symbol with template arguments.
-     In this case the symbol is really a "struct template_symbol".  */
-  unsigned is_cplus_template_function : 1;
-
-  /* True if this is a Rust virtual table.  In this case, the symbol
-     can be downcast to "struct rust_vtable_symbol".  */
+  /* The concrete type of this symbol.  */
 
-  unsigned is_rust_vtable : 1;
+  ENUM_BITFIELD (symbol_subclass_kind) subclass : 2;
 
   /* Line number of this symbol's definition, except for inlined
      functions.  For an inlined function (class LOC_BLOCK and
@@ -1126,7 +1136,7 @@ extern const struct block_symbol null_block_symbol;
 #define SYMBOL_IS_ARGUMENT(symbol)	(symbol)->is_argument
 #define SYMBOL_INLINED(symbol)		(symbol)->is_inlined
 #define SYMBOL_IS_CPLUS_TEMPLATE_FUNCTION(symbol) \
-  (symbol)->is_cplus_template_function
+  (((symbol)->subclass) == SYMBOL_TEMPLATE)
 #define SYMBOL_TYPE(symbol)		(symbol)->type
 #define SYMBOL_LINE(symbol)		(symbol)->line
 #define SYMBOL_COMPUTED_OPS(symbol)	(SYMBOL_IMPL (symbol).ops_computed)
-- 
2.9.5