Use native alignment to access Lisp object data

Instead of using __builtin_assume_aligned (P, GCALIGNMENT) to
tell GCC that P has alignment 8, use (T *) P where T is the
type of the pointed-to object, to tell GCC that P has native
alignment.  This is simpler, matches the intent better, and
should help simplify future improvements.  Some of these
changes are to pacify gcc -Wnull-dereference, since GCC is
smarter about pointers now that Emacs no longer uses
__builtin_assume_aligned; these minor changes should improve
code efficiency slightly.  On Fedora 28 x86-64 with default
optimization this patch shrinks the size of the Emacs text
segment by 0.36%.
* src/conf_post.h (__has_builtin, __builtin_assume_aligned):
Remove; no longer used.
* src/dbusbind.c (XD_OBJECT_TO_DBUS_TYPE):
Pacify -Wnull-dereference by using XCAR instead of CAR_SAFE
and XCDR instead of CDR_SAFE when this is safe.
* src/fileio.c (Fexpand_file_name):
* src/font.c (clear_font_cache):
Pacify -Wnull-dereference by removing unnecessary NILP test.
* src/keyboard.c (xevent_start): New function.
(read_char, read_key_sequence): Pacify -Wnull-dereference by
using xevent_start instead of EVENT_START.
* src/lisp.h (lisp_h_XUNTAG): Remove; XUNTAG is always a macro
now, since it can no longer be implemented as a function.
(XUNTAG): New third argument CTYPE.  All uses changed.
Cast result to CTYPE * instead of using __builtin_assume_aligned.
Simplify by using LISP_WORD_TAG.
(LISP_WORD_TAG): New macro.
(TAG_PTR): Use it.
* src/menu.c (x_popup_menu_1):
Pacify -Wnull-dereference by using XCAR instead of Fcar and
XCDR instead of Fcdr where this is safe.

1 files changed, 10 insertions, 8 deletions

diff --git a/src/dbusbind.c b/src/dbusbind.c
index ec3707d18f3..4e0b99bea9d 100644
--- a/src/dbusbind.c
+++ b/src/dbusbind.c
@@ -207,10 +207,10 @@ xd_symbol_to_dbus_type (Lisp_Object object)
    : (STRINGP (object)) ? DBUS_TYPE_STRING				\
    : (XD_DBUS_TYPE_P (object)) ? xd_symbol_to_dbus_type (object)	\
    : (CONSP (object))							\
-   ? ((XD_DBUS_TYPE_P (CAR_SAFE (object)))				\
-      ? ((XD_BASIC_DBUS_TYPE (xd_symbol_to_dbus_type (CAR_SAFE (object)))) \
+   ? ((XD_DBUS_TYPE_P (XCAR (object)))					\
+      ? ((XD_BASIC_DBUS_TYPE (xd_symbol_to_dbus_type (XCAR (object))))	\
 	 ? DBUS_TYPE_ARRAY						\
-	 : xd_symbol_to_dbus_type (CAR_SAFE (object)))			\
+	 : xd_symbol_to_dbus_type (XCAR (object)))			\
       : DBUS_TYPE_ARRAY)						\
    : DBUS_TYPE_INVALID)
 
@@ -396,7 +396,7 @@ xd_signature (char *signature, int dtype, int parent_type, Lisp_Object object)
       CHECK_CONS (object);
 
       /* Type symbol is optional.  */
-      if (EQ (QCarray, CAR_SAFE (elt)))
+      if (EQ (QCarray, XCAR (elt)))
 	elt = XD_NEXT_VALUE (elt);
 
       /* If the array is empty, DBUS_TYPE_STRING is the default
@@ -416,10 +416,12 @@ xd_signature (char *signature, int dtype, int parent_type, Lisp_Object object)
       /* If the element type is DBUS_TYPE_SIGNATURE, and this is the
 	 only element, the value of this element is used as the
 	 array's element signature.  */
-      if ((subtype == DBUS_TYPE_SIGNATURE)
-	  && STRINGP (CAR_SAFE (XD_NEXT_VALUE (elt)))
-	  && NILP (CDR_SAFE (XD_NEXT_VALUE (elt))))
-	subsig = SSDATA (CAR_SAFE (XD_NEXT_VALUE (elt)));
+      if (subtype == DBUS_TYPE_SIGNATURE)
+	{
+	  Lisp_Object elt1 = XD_NEXT_VALUE (elt);
+	  if (CONSP (elt1) && STRINGP (XCAR (elt1)) && NILP (XCDR (elt1)))
+	    subsig = SSDATA (XCAR (elt1));
+	}
 
       while (!NILP (elt))
 	{