Patch: reduce size of cp_token

[Tom Tromey <tromey at redhat dot com>]

My earlier patch to remove input_file_stack also removed a field from
struct cp_token.  This made it possible to reduce the size of this
struct.

This patch rearranges cp_token.  On my x86 box it now takes 12 bytes
rather than 16.  This patch reduces the size of cp_token::type by one
bit, but it also adds a compile-time assertion to ensure that we don't
overflow this.  I've also moved the 'location' field earlier to get
better packing on a 64-bit machine, though I did not actually verify
this in action.  I also did not try to measure how much memory this
saves.

Bootstrapped & regtested on x86 FC-6.  Ok?

Tom

cp/ChangeLog:
2008-02-29  Tom Tromey  <tromey@redhat.com>

	* parser.c (CP_TOKEN_BITS): New define.
	(struct cp_token) <type>: Use it.
	(struct cp_token) <ambiguous_p>: Move earlier.
	(struct cp_token) <location>: Move earlier.
	(cp_token_size_self_check): Declare.
	(eof_token): Update.

Index: cp/parser.c
===================================================================
--- cp/parser.c	(revision 132775)
+++ cp/parser.c	(working copy)
@@ -58,12 +58,20 @@
   tree qualifying_scope;
 };
 
-/* A C++ token.  */
+/* Number of bits used to represent a token in struct cp_token.  */
+#define CP_TOKEN_BITS 7
 
+/* A C++ token.  Note that this is carefully laid out to have the
+   least amount of padding.  */
+
 typedef struct cp_token GTY (())
 {
   /* The kind of token.  */
-  ENUM_BITFIELD (cpp_ttype) type : 8;
+  ENUM_BITFIELD (cpp_ttype) type : CP_TOKEN_BITS;
+  /* True for a CPP_NAME token that is not a keyword (i.e., for which
+     KEYWORD is RID_MAX) iff this name was looked up and found to be
+     ambiguous.  An error has already been reported.  */
+  BOOL_BITFIELD ambiguous_p : 1;
   /* If this token is a keyword, this value indicates which keyword.
      Otherwise, this value is RID_MAX.  */
   ENUM_BITFIELD (rid) keyword : 8;
@@ -75,10 +83,8 @@
   BOOL_BITFIELD in_system_header : 1;
   /* True if this token is from a context where it is implicitly extern "C" */
   BOOL_BITFIELD implicit_extern_c : 1;
-  /* True for a CPP_NAME token that is not a keyword (i.e., for which
-     KEYWORD is RID_MAX) iff this name was looked up and found to be
-     ambiguous.  An error has already been reported.  */
-  BOOL_BITFIELD ambiguous_p : 1;
+  /* The location at which this token was found.  */
+  location_t location;
   /* The value associated with this token, if any.  */
   union cp_token_value {
     /* Used for CPP_NESTED_NAME_SPECIFIER and CPP_TEMPLATE_ID.  */
@@ -86,8 +92,6 @@
     /* Use for all other tokens.  */
     tree GTY((tag ("0"))) value;
   } GTY((desc ("(%1.type == CPP_TEMPLATE_ID) || (%1.type == CPP_NESTED_NAME_SPECIFIER)"))) u;
-  /* The location at which this token was found.  */
-  location_t location;
 } cp_token;
 
 /* We use a stack of token pointer for saving token sets.  */
@@ -97,8 +101,7 @@
 
 static cp_token eof_token =
 {
-  CPP_EOF, RID_MAX, 0, PRAGMA_NONE, 0, false, 0, { NULL },
-  0
+  CPP_EOF, false, RID_MAX, 0, PRAGMA_NONE, 0, false, 0, { NULL }
 };
 
 /* The cp_lexer structure represents the C++ lexer.  It is responsible
@@ -246,6 +249,9 @@
 /* The number of token types, including C++-specific ones.  */
 #define N_CP_TTYPES ((int) (CPP_PURGED + 1))
 
+/* Self-check that we have enough bits reserved in cp_token.  */
+extern int cp_token_size_self_check[(N_CP_TTYPES <= (1 << CP_TOKEN_BITS)) ? 1 : -1];
+
 /* Variables.  */
 
 #ifdef ENABLE_CHECKING