Re: Redundant type checking in window.c and w32menu.c

[Dmitry Antipov <dmantipov@yandex.ru>]

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Ken Raeburn wrote:

> On Jun 19, 2007, at 10:44, Dmitry Antipov wrote:
>> If we pass CHECK_CONS(), we don't need CONSP()s in Fcar() and Fcdr() 
>> and may use XCAR()
>> and XCDR() instead.
> 
> Makes sense.

Whoops, probably not for GNU C :-). At least with -O1 and -O2, GCC (I've
tested with 4.1.2) emits an almost identical and optimal (i.e. with the
only branch ends with a call of wrong_type_argument ()) code for both cases

CHECK_CONS (obj);
x = CAR (obj);
y = CDR (obj);

and

CHECK_CONS (obj);
x = XCAR (obj);
y = XCDR (obj);

Have no ideas about other compilers.

> You could make Fcar a static inline function in lisp.h (conditional on 
> GCC, or maybe C99).  If the optimizer's good at its job, it should 
> eliminate the redundant CONSP checks.  Using an inline function avoids 
> having to check all Fcar uses for arguments that have function calls or 
> side effects.  (A quick grep shows several of those.  In fact, if your 
> test used the simple macro version, inline functions may result in less 
> code size expansion because of this.)  And personally, I think inline 
> functions are often more readable than macros, if they're not very 
> simple macros.

I agree, and here is the stuff I'm trying now. Reordering of data.c
looks ugly, but I have no ideas on how to avoid them :-(.

Dmitry

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Index: data.c
===================================================================
RCS file: /sources/emacs/emacs/src/data.c,v
retrieving revision 1.271
diff -u -r1.271 data.c
--- data.c	26 May 2007 17:21:14 -0000	1.271
+++ data.c	20 Jun 2007 14:11:00 -0000
@@ -506,49 +506,6 @@
   return Qnil;
 }
 
-\f
-/* Extract and set components of lists */
-
-DEFUN ("car", Fcar, Scar, 1, 1, 0,
-       doc: /* Return the car of LIST.  If arg is nil, return nil.
-Error if arg is not nil and not a cons cell.  See also `car-safe'.
-
-See Info node `(elisp)Cons Cells' for a discussion of related basic
-Lisp concepts such as car, cdr, cons cell and list.  */)
-     (list)
-     register Lisp_Object list;
-{
-  return CAR (list);
-}
-
-DEFUN ("car-safe", Fcar_safe, Scar_safe, 1, 1, 0,
-       doc: /* Return the car of OBJECT if it is a cons cell, or else nil.  */)
-     (object)
-     Lisp_Object object;
-{
-  return CAR_SAFE (object);
-}
-
-DEFUN ("cdr", Fcdr, Scdr, 1, 1, 0,
-       doc: /* Return the cdr of LIST.  If arg is nil, return nil.
-Error if arg is not nil and not a cons cell.  See also `cdr-safe'.
-
-See Info node `(elisp)Cons Cells' for a discussion of related basic
-Lisp concepts such as cdr, car, cons cell and list.  */)
-     (list)
-     register Lisp_Object list;
-{
-  return CDR (list);
-}
-
-DEFUN ("cdr-safe", Fcdr_safe, Scdr_safe, 1, 1, 0,
-       doc: /* Return the cdr of OBJECT if it is a cons cell, or else nil.  */)
-     (object)
-     Lisp_Object object;
-{
-  return CDR_SAFE (object);
-}
-
 DEFUN ("setcar", Fsetcar, Ssetcar, 2, 2, 0,
        doc: /* Set the car of CELL to be NEWCAR.  Returns NEWCAR.  */)
      (cell, newcar)
@@ -2933,6 +2890,57 @@
   return make_number (order);
 }
 
+#if defined (__GNUC__) && defined (__OPTIMIZE__) && !defined(__OPTIMIZE_SIZE__)
+/* If we're optimizing, these are macros, and they will conflict with
+   the definitions below.  */
+#undef Fcar
+#undef Fcar_safe
+#undef Fcdr
+#undef Fcdr_safe
+#endif
+
+\f
+/* Extract and set components of lists */
+
+DEFUN ("car", Fcar, Scar, 1, 1, 0,
+       doc: /* Return the car of LIST.  If arg is nil, return nil.
+Error if arg is not nil and not a cons cell.  See also `car-safe'.
+
+See Info node `(elisp)Cons Cells' for a discussion of related basic
+Lisp concepts such as car, cdr, cons cell and list.  */)
+     (list)
+     register Lisp_Object list;
+{
+  return CAR (list);
+}
+
+DEFUN ("car-safe", Fcar_safe, Scar_safe, 1, 1, 0,
+       doc: /* Return the car of OBJECT if it is a cons cell, or else nil.  */)
+     (object)
+     Lisp_Object object;
+{
+  return CAR_SAFE (object);
+}
+
+DEFUN ("cdr", Fcdr, Scdr, 1, 1, 0,
+       doc: /* Return the cdr of LIST.  If arg is nil, return nil.
+Error if arg is not nil and not a cons cell.  See also `cdr-safe'.
+
+See Info node `(elisp)Cons Cells' for a discussion of related basic
+Lisp concepts such as cdr, car, cons cell and list.  */)
+     (list)
+     register Lisp_Object list;
+{
+  return CDR (list);
+}
+
+DEFUN ("cdr-safe", Fcdr_safe, Scdr_safe, 1, 1, 0,
+       doc: /* Return the cdr of OBJECT if it is a cons cell, or else nil.  */)
+     (object)
+     Lisp_Object object;
+{
+  return CDR_SAFE (object);
+}
 
 \f
 void
Index: lisp.h
===================================================================
RCS file: /sources/emacs/emacs/src/lisp.h,v
retrieving revision 1.577
diff -u -r1.577 lisp.h
--- lisp.h	8 Jun 2007 19:56:24 -0000	1.577
+++ lisp.h	20 Jun 2007 14:11:00 -0000
@@ -2206,10 +2206,39 @@
 EXFUN (Finteger_or_floatp, 1);
 EXFUN (Finteger_or_float_or_marker_p, 1);
 
+/* If using GNU and optimizing for speed,
+   inline the most common cons operations.  */
+#if defined (__GNUC__) && defined (__OPTIMIZE__) && !defined(__OPTIMIZE_SIZE__)
+
+#define CONSFN(name) \
+  static __inline__ Lisp_Object \
+  _F ## name (obj) \
+       Lisp_Object obj; \
+  { \
+    return name (obj); \
+  }
+
+CONSFN (CAR)
+CONSFN (CAR_SAFE)
+CONSFN (CDR)
+CONSFN (CDR_SAFE)
+
+#define Fcar(c) _FCAR (c)
+#define Fcar_safe(c) _FCAR_SAFE (c)
+#define Fcdr(c) _FCDR (c)
+#define Fcdr_safe(c) _FCDR_SAFE (c)
+
+#undef CONSFN
+
+#else
+
 EXFUN (Fcar, 1);
 EXFUN (Fcar_safe, 1);
 EXFUN (Fcdr, 1);
 EXFUN (Fcdr_safe, 1);
+
+#endif /* __GNUC__ && __OPTIMIZE__ && !__OPTIMIZE_SIZE__ */
+
 EXFUN (Fsetcar, 2);
 EXFUN (Fsetcdr, 2);
 EXFUN (Fboundp, 1);

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