Commit bc78ff26 authored by Paul Eggert's avatar Paul Eggert
Browse files

Use 0 for Qnil

Fixes Bug#15880.
If USE_LSB_TAG, arrange for the representation of Qnil to be zero so
that NILP (x) is equivalent to testing whether x is 0 at the
machine level.  The overall effects of this and the previous patch
shrink the size of the text segment by 2.3% and speeds up
compilation of all the .elc files by about 0.5% on my platform,
which is Fedora 20 x86-64.
* lib-src/make-docfile.c (compare_globals):
* src/lisp.h (lisp_h_XPNTR, lisp_h_XSYMBOL, lisp_h_XUNTAG)
(make_lisp_symbol) [USE_LSB_TAG]:
Symbols now tag the difference from lispsym, not the pointer.
(lisp_h_XUNTAGBASE, TAG_SYMPTR): New macros.
(Lisp_Int0, Lisp_Int1, Lisp_Symbol, Lisp_Misc, Lisp_String, Lisp_Cons):
Renumber so that Lisp_Symbol is 0, so that Qnil is zero.
(XSYMBOL): New forward decl.
(XUNTAGBASE): New function.
(XUNTAG): Use it.
parent 58f2d6ef
2015-01-05 Paul Eggert <eggert@cs.ucla.edu>
Use 0 for Qnil
* make-docfile.c (compare_globals): Consider 'nil' to be the least.
Compute C decls for DEFSYMs automatically
Fixes Bug#15880.
* make-docfile.c: Revamp to generate table of symbols, too.
......
......@@ -613,6 +613,16 @@ compare_globals (const void *a, const void *b)
if (ga->type != gb->type)
return ga->type - gb->type;
/* Consider "nil" to be the least, so that aQnil is firat. That
way, Qnil's internal representation is zero, which is a bit faster. */
if (ga->type == SYMBOL)
{
bool a_nil = strcmp (ga->name, "Qnil") == 0;
bool b_nil = strcmp (gb->name, "Qnil") == 0;
if (a_nil | b_nil)
return b_nil - a_nil;
}
return strcmp (ga->name, gb->name);
}
......
2015-01-05 Paul Eggert <eggert@cs.ucla.edu>
 
Use 0 for Qnil
Fixes Bug#15880.
If USE_LSB_TAG, arrange for the representation of Qnil to be zero so
that NILP (x) is equivalent to testing whether x is 0 at the
machine level. The overall effects of this and the previous patch
shrink the size of the text segment by 2.3% and speeds up
compilation of all the .elc files by about 0.5% on my platform,
which is Fedora 20 x86-64.
* lisp.h (lisp_h_XPNTR, lisp_h_XSYMBOL, lisp_h_XUNTAG)
(make_lisp_symbol) [USE_LSB_TAG]:
Symbols now tag the difference from lispsym, not the pointer.
(lisp_h_XUNTAGBASE, TAG_SYMPTR): New macros.
(Lisp_Int0, Lisp_Int1, Lisp_Symbol, Lisp_Misc, Lisp_String, Lisp_Cons):
Renumber so that Lisp_Symbol is 0, so that Qnil is zero.
(XSYMBOL): New forward decl.
(XUNTAGBASE): New function.
(XUNTAG): Use it.
Compute C decls for DEFSYMs automatically
Fixes Bug#15880.
This patch also makes Q constants (e.g., Qnil) constant addresses
......
......@@ -354,9 +354,11 @@ error !;
#define lisp_h_XCONS(a) \
(eassert (CONSP (a)), (struct Lisp_Cons *) XUNTAG (a, Lisp_Cons))
#define lisp_h_XHASH(a) XUINT (a)
#define lisp_h_XPNTR(a) ((void *) (intptr_t) (XLI (a) & VALMASK))
#define lisp_h_XPNTR(a) \
(SYMBOLP (a) ? XSYMBOL (a) : (void *) ((intptr_t) (XLI (a) & VALMASK)))
#define lisp_h_XSYMBOL(a) \
(eassert (SYMBOLP (a)), (struct Lisp_Symbol *) XUNTAG (a, Lisp_Symbol))
(eassert (SYMBOLP (a)), \
(struct Lisp_Symbol *) XUNTAGBASE (a, Lisp_Symbol, lispsym))
#ifndef GC_CHECK_CONS_LIST
# define lisp_h_check_cons_list() ((void) 0)
#endif
......@@ -366,7 +368,9 @@ error !;
# define lisp_h_XFASTINT(a) XINT (a)
# define lisp_h_XINT(a) (XLI (a) >> INTTYPEBITS)
# define lisp_h_XTYPE(a) ((enum Lisp_Type) (XLI (a) & ~VALMASK))
# define lisp_h_XUNTAG(a, type) ((void *) (XLI (a) - (type)))
# define lisp_h_XUNTAG(a, type) XUNTAGBASE (a, type, 0)
# define lisp_h_XUNTAGBASE(a, type, base) \
((void *) ((char *) (base) - (type) + (intptr_t) XLI (a)))
#endif
/* When compiling via gcc -O0, define the key operations as macros, as
......@@ -408,6 +412,7 @@ error !;
# define XINT(a) lisp_h_XINT (a)
# define XTYPE(a) lisp_h_XTYPE (a)
# define XUNTAG(a, type) lisp_h_XUNTAG (a, type)
# define XUNTAGBASE(a, type, base) lisp_h_XUNTAGBASE (a, type, base)
# endif
#endif
......@@ -447,20 +452,20 @@ error !;
enum Lisp_Type
{
/* Integer. XINT (obj) is the integer value. */
Lisp_Int0 = 0,
Lisp_Int1 = USE_LSB_TAG ? 1 << INTTYPEBITS : 1,
/* Symbol. XSYMBOL (object) points to a struct Lisp_Symbol. */
Lisp_Symbol = 2,
Lisp_Symbol = 0,
/* Miscellaneous. XMISC (object) points to a union Lisp_Misc,
whose first member indicates the subtype. */
Lisp_Misc = 3,
Lisp_Misc = 1,
/* Integer. XINT (obj) is the integer value. */
Lisp_Int0 = 2,
Lisp_Int1 = USE_LSB_TAG ? 6 : 3,
/* String. XSTRING (object) points to a struct Lisp_String.
The length of the string, and its contents, are stored therein. */
Lisp_String = USE_LSB_TAG ? 1 : 1 << INTTYPEBITS,
Lisp_String = 4,
/* Vector of Lisp objects, or something resembling it.
XVECTOR (object) points to a struct Lisp_Vector, which contains
......@@ -469,7 +474,7 @@ enum Lisp_Type
Lisp_Vectorlike = 5,
/* Cons. XCONS (object) points to a struct Lisp_Cons. */
Lisp_Cons = 6,
Lisp_Cons = USE_LSB_TAG ? 3 : 6,
Lisp_Float = 7
};
......@@ -604,6 +609,8 @@ INLINE bool SUB_CHAR_TABLE_P (Lisp_Object);
INLINE bool SUBRP (Lisp_Object);
INLINE bool (SYMBOLP) (Lisp_Object);
INLINE bool (VECTORLIKEP) (Lisp_Object);
INLINE struct Lisp_Symbol *XSYMBOL (Lisp_Object);
INLINE void *(XUNTAGBASE) (Lisp_Object, int, void *);
INLINE bool WINDOWP (Lisp_Object);
INLINE struct Lisp_Save_Value *XSAVE_VALUE (Lisp_Object);
......@@ -720,6 +727,10 @@ struct Lisp_Symbol
#define TAG_PTR(tag, ptr) \
((USE_LSB_TAG ? (tag) : (EMACS_UINT) (tag) << VALBITS) + (uintptr_t) (ptr))
/* Yield an integer that tags PTR as a symbol. */
#define TAG_SYMPTR(ptr) \
TAG_PTR (Lisp_Symbol, (char *) (ptr) - (char *) (USE_LSB_TAG ? lispsym : 0))
/* Declare extern constants for Lisp symbols. These can be helpful
when using a debugger like GDB, on older platforms where the debug
format does not represent C macros. Athough these symbols are
......@@ -727,7 +738,7 @@ struct Lisp_Symbol
#define DEFINE_LISP_SYMBOL_BEGIN(name) \
DEFINE_GDB_SYMBOL_BEGIN (Lisp_Object, name)
#define DEFINE_LISP_SYMBOL_END(name) \
DEFINE_GDB_SYMBOL_END (LISP_INITIALLY (TAG_PTR (Lisp_Symbol, name)))
DEFINE_GDB_SYMBOL_END (LISP_INITIALLY (TAG_SYMPTR (name)))
#include "globals.h"
......@@ -818,6 +829,8 @@ LISP_MACRO_DEFUN (XINT, EMACS_INT, (Lisp_Object a), (a))
LISP_MACRO_DEFUN (XFASTINT, EMACS_INT, (Lisp_Object a), (a))
LISP_MACRO_DEFUN (XTYPE, enum Lisp_Type, (Lisp_Object a), (a))
LISP_MACRO_DEFUN (XUNTAG, void *, (Lisp_Object a, int type), (a, type))
LISP_MACRO_DEFUN (XUNTAGBASE, void *, (Lisp_Object a, int type, void *base),
(a, type, base))
#else /* ! USE_LSB_TAG */
......@@ -878,16 +891,21 @@ XTYPE (Lisp_Object a)
return USE_LSB_TAG ? i & ~VALMASK : i >> VALBITS;
}
/* Extract A's pointer value, assuming A's type is TYPE.
If USE_LSB_TAG, add BASE to A's pointer value while extracting. */
INLINE void *
XUNTAGBASE (Lisp_Object a, int type, void *base)
{
char *b = USE_LSB_TAG ? base : 0;
intptr_t i = USE_LSB_TAG ? XLI (a) - type : XLI (a) & VALMASK;
return b + i;
}
/* Extract A's pointer value, assuming A's type is TYPE. */
INLINE void *
XUNTAG (Lisp_Object a, int type)
{
if (USE_LSB_TAG)
{
intptr_t i = XLI (a) - type;
return (void *) i;
}
return XPNTR (a);
return XUNTAGBASE (a, type, 0);
}
#endif /* ! USE_LSB_TAG */
......@@ -1032,7 +1050,10 @@ make_lisp_ptr (void *ptr, enum Lisp_Type type)
INLINE Lisp_Object
make_lisp_symbol (struct Lisp_Symbol *sym)
{
return make_lisp_ptr (sym, Lisp_Symbol);
Lisp_Object a = XIL (TAG_SYMPTR (sym));
eassert (XTYPE (a) == Lisp_Symbol
&& XUNTAGBASE (a, Lisp_Symbol, lispsym) == sym);
return a;
}
INLINE Lisp_Object
......
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