Better isolate code that assumes NIL_IS_ZERO

Suggested by Stefan Monnier in:
http://lists.gnu.org/archive/html/emacs-devel/2015-01/msg00588.html
* alloc.c (allocate_pseudovector):
Use memclear, not memsetnil, to remove a 'verify'.
* callint.c (Fcall_interactively):
* dispnew.c (realloc_glyph_pool):
* xdisp.c (init_iterator):
Use memclear, not memset, to remove a 'verify'.
* lisp.h (memclear): Rename from memsetnil, and take a byte
count rather than a word count.  All callers changed.

src/ChangeLog

@@ -1,3 +1,17 @@
+2015-01-22  Paul Eggert  <eggert@cs.ucla.edu>
+
+	Isolate NIL_IS_ZERO-assuming code better
+	Suggested by Stefan Monnier in:
+	http://lists.gnu.org/archive/html/emacs-devel/2015-01/msg00588.html
+	* alloc.c (allocate_pseudovector):
+	Use memclear, not memsetnil, to remove a 'verify'.
+	* callint.c (Fcall_interactively):
+	* dispnew.c (realloc_glyph_pool):
+	* xdisp.c (init_iterator):
+	Use memclear, not memset, to remove a 'verify'.
+	* lisp.h (memclear): Rename from memsetnil, and take a byte
+	count rather than a word count.  All callers changed.
+
 2015-01-20  Paul Eggert  <eggert@cs.ucla.edu>
 
 	Undo port to hypothetical nonzero Qnil case

src/alloc.c

@@ -3174,11 +3174,8 @@ allocate_pseudovector (int memlen, int lisplen,
   eassert (memlen - lisplen <= (1 << PSEUDOVECTOR_REST_BITS) - 1);
   eassert (lisplen <= (1 << PSEUDOVECTOR_SIZE_BITS) - 1);
 
-  /* Only the first LISPLEN slots will be traced normally by the GC.
-     Since Qnil == 0, we can memset Lisp and non-Lisp data at one go.  */
-  verify (NIL_IS_ZERO);
-  memsetnil (v->contents, zerolen);
-
+  /* Only the first LISPLEN slots will be traced normally by the GC.  */
+  memclear (v->contents, zerolen * word_size);
   XSETPVECTYPESIZE (v, tag, lisplen, memlen - lisplen);
   return v;
 }

src/callint.c

@@ -509,8 +509,7 @@ invoke it.  If KEYS is omitted or nil, the return value of
   visargs = args + nargs;
   varies = (signed char *) (visargs + nargs);
 
-  verify (NIL_IS_ZERO);
-  memset (args, 0, nargs * (2 * word_size + 1));
+  memclear (args, nargs * (2 * word_size + 1));
 
   GCPRO5 (prefix_arg, function, *args, *visargs, up_event);
   gcpro3.nvars = nargs;

src/coding.c

@@ -11273,7 +11273,7 @@ internal character representation.  */);
 
   {
     Lisp_Object args[coding_arg_undecided_max];
-    memsetnil (args, ARRAYELTS (args));
+    memclear (args, sizeof args);
 
     Lisp_Object plist[16];
     plist[0] = intern_c_string (":name");

src/dispnew.c

@@ -1339,14 +1339,8 @@ realloc_glyph_pool (struct glyph_pool *pool, struct dim matrix_dim)
       ptrdiff_t old_nglyphs = pool->nglyphs;
       pool->glyphs = xpalloc (pool->glyphs, &pool->nglyphs,
 			      needed - old_nglyphs, -1, sizeof *pool->glyphs);
-
-      /* Redisplay relies on nil as the object of special glyphs
-	 (truncation and continuation glyphs and also blanks used to
-	 extend each line on a TTY), so verify that memset does this.  */
-      verify (NIL_IS_ZERO);
-
-      memset (pool->glyphs + old_nglyphs, 0,
-	      (pool->nglyphs - old_nglyphs) * sizeof *pool->glyphs);
+      memclear (pool->glyphs + old_nglyphs,
+		(pool->nglyphs - old_nglyphs) * sizeof *pool->glyphs);
     }
 
   /* Remember the number of rows and columns because (a) we use them

src/eval.c

@@ -2299,7 +2299,8 @@ usage: (apply FUNCTION &rest ARGUMENTS)  */)
       /* Avoid making funcall cons up a yet another new vector of arguments
 	 by explicitly supplying nil's for optional values.  */
       SAFE_ALLOCA_LISP (funcall_args, 1 + XSUBR (fun)->max_args);
-      memsetnil (funcall_args + numargs + 1, XSUBR (fun)->max_args - numargs);
+      memclear (funcall_args + numargs + 1,
+		(XSUBR (fun)->max_args - numargs) * word_size);
       funcall_nargs = 1 + XSUBR (fun)->max_args;
     }
   else
@@ -2693,8 +2694,8 @@ usage: (funcall FUNCTION &rest ARGUMENTS)  */)
 	      eassert (XSUBR (fun)->max_args <= ARRAYELTS (internal_argbuf));
 	      internal_args = internal_argbuf;
 	      memcpy (internal_args, args + 1, numargs * word_size);
-	      memsetnil (internal_args + numargs,
-			 XSUBR (fun)->max_args - numargs);
+	      memclear (internal_args + numargs,
+			(XSUBR (fun)->max_args - numargs) * word_size);
 	    }
 	  else
 	    internal_args = args + 1;

src/fns.c

@@ -2524,7 +2524,7 @@ mapcar1 (EMACS_INT leni, Lisp_Object *vals, Lisp_Object fn, Lisp_Object seq)
   if (vals)
     {
       /* Don't let vals contain any garbage when GC happens.  */
-      memsetnil (vals, leni);
+      memclear (vals, leni * word_size);
 
       GCPRO3 (dummy, fn, seq);
       gcpro1.var = vals;
@@ -3700,7 +3700,7 @@ larger_vector (Lisp_Object vec, ptrdiff_t incr_min, ptrdiff_t nitems_max)
   new_size = old_size + incr;
   v = allocate_vector (new_size);
   memcpy (v->contents, XVECTOR (vec)->contents, old_size * sizeof *v->contents);
-  memsetnil (v->contents + old_size, new_size - old_size);
+  memclear (v->contents + old_size, incr * word_size);
   XSETVECTOR (vec, v);
   return vec;
 }

src/font.c

@@ -989,14 +989,14 @@ font_expand_wildcards (Lisp_Object *field, int n)
 	  if (i == 0 || ! NILP (tmp[i - 1]))
 	    /* None of TMP[X] corresponds to Jth field.  */
 	    return -1;
-	  memsetnil (field + j, range[i].from - j);
+	  memclear (field + j, (range[i].from - j) * word_size);
 	  j = range[i].from;
 	}
       field[j++] = tmp[i];
     }
   if (! NILP (tmp[n - 1]) && j < XLFD_REGISTRY_INDEX)
     return -1;
-  memsetnil (field + j, XLFD_LAST_INDEX - j);
+  memclear (field + j, (XLFD_LAST_INDEX - j) * word_size);
   if (INTEGERP (field[XLFD_ENCODING_INDEX]))
     field[XLFD_ENCODING_INDEX]
       = Fintern (Fnumber_to_string (field[XLFD_ENCODING_INDEX]), Qnil);

src/lisp.h

@@ -1508,13 +1508,15 @@ gc_aset (Lisp_Object array, ptrdiff_t idx, Lisp_Object val)
    to find such assumptions later if we change Qnil to be nonzero.  */
 enum { NIL_IS_ZERO = XLI_BUILTIN_LISPSYM (iQnil) == 0 };
 
-/* Set a Lisp_Object array V's N entries to nil.  */
+/* Clear the object addressed by P, with size NBYTES, so that all its
+   bytes are zero and all its Lisp values are nil.  */
 INLINE void
-memsetnil (Lisp_Object *v, ptrdiff_t n)
+memclear (void *p, ptrdiff_t nbytes)
 {
-  eassert (0 <= n);
+  eassert (0 <= nbytes);
   verify (NIL_IS_ZERO);
-  memset (v, 0, n * sizeof *v);
+  /* Since Qnil is zero, memset suffices.  */
+  memset (p, 0, nbytes);
 }
 
 /* If a struct is made to look like a vector, this macro returns the length

src/xdisp.c

@@ -2746,13 +2746,7 @@ init_iterator (struct it *it, struct window *w,
 	row = MATRIX_HEADER_LINE_ROW (w->desired_matrix);
     }
 
-  /* Clear IT.  */
-
-  /* The code assumes it->object and other Lisp_Object components are
-     set to nil, so verify that memset does this.  */
-  verify (NIL_IS_ZERO);
-  memset (it, 0, sizeof *it);
-
+  memclear (it, sizeof *it);
   it->current.overlay_string_index = -1;
   it->current.dpvec_index = -1;
   it->base_face_id = remapped_base_face_id;