Change vectorlike from struct to union

* src/lisp.h (vectorlike_headed): Change from struct to union.
All uses changed.  Since it has only one member, this does not
change semantics.  This is designed to simplify future changes
needed to fix bugs like Bug#29040.  All uses changed.

doc/lispref/internals.texi

@@ -248,7 +248,7 @@ of 8k bytes, and small vectors are packed into blocks of 4k bytes).
 @cindex storage of vector-like Lisp objects
   Beyond the basic vector, a lot of objects like window, buffer, and
 frame are managed as if they were vectors.  The corresponding C data
-structures include the @code{struct vectorlike_header} field whose
+structures include the @code{union vectorlike_header} field whose
 @code{size} member contains the subtype enumerated by @code{enum pvec_type}
 and an information about how many @code{Lisp_Object} fields this structure
 contains and what the size of the rest data is.  This information is
@@ -1085,7 +1085,7 @@ Some of the fields of @code{struct buffer} are:
 
 @table @code
 @item header
-A header of type @code{struct vectorlike_header} is common to all
+A header of type @code{union vectorlike_header} is common to all
 vectorlike objects.
 
 @item own_text

src/buffer.h

@@ -504,7 +504,7 @@ struct buffer_text
 
 struct buffer
 {
-  struct vectorlike_header header;
+  union vectorlike_header header;
 
   /* The name of this buffer.  */
   Lisp_Object name_;

src/font.h

@@ -244,7 +244,7 @@ enum font_property_index
 
 struct font_spec
 {
-  struct vectorlike_header header;
+  union vectorlike_header header;
   Lisp_Object props[FONT_SPEC_MAX];
 };
 
@@ -252,7 +252,7 @@ struct font_spec
 
 struct font_entity
 {
-  struct vectorlike_header header;
+  union vectorlike_header header;
   Lisp_Object props[FONT_ENTITY_MAX];
 };
 
@@ -265,7 +265,7 @@ struct font_entity
 
 struct font
 {
-  struct vectorlike_header header;
+  union vectorlike_header header;
 
   /* All Lisp_Object components must come first.
      That ensures they are all aligned normally.  */

src/frame.h

@@ -79,7 +79,7 @@ enum ns_appearance_type
 
 struct frame
 {
-  struct vectorlike_header header;
+  union vectorlike_header header;
 
   /* All Lisp_Object components must come first.
      That ensures they are all aligned normally.  */

src/lisp.h

@@ -796,11 +796,11 @@ struct Lisp_Symbol
 /* Header of vector-like objects.  This documents the layout constraints on
    vectors and pseudovectors (objects of PVEC_xxx subtype).  It also prevents
    compilers from being fooled by Emacs's type punning: XSETPSEUDOVECTOR
-   and PSEUDOVECTORP cast their pointers to struct vectorlike_header *,
+   and PSEUDOVECTORP cast their pointers to union vectorlike_header *,
    because when two such pointers potentially alias, a compiler won't
    incorrectly reorder loads and stores to their size fields.  See
    Bug#8546.  */
-struct vectorlike_header
+union vectorlike_header
   {
     /* The only field contains various pieces of information:
        - The MSB (ARRAY_MARK_FLAG) holds the gcmarkbit.
@@ -1094,10 +1094,10 @@ INLINE bool
 		       | ((restsize) << PSEUDOVECTOR_SIZE_BITS) \
 		       | (lispsize)))
 
-/* The cast to struct vectorlike_header * avoids aliasing issues.  */
+/* The cast to union vectorlike_header * avoids aliasing issues.  */
 #define XSETPSEUDOVECTOR(a, b, code) \
   XSETTYPED_PSEUDOVECTOR (a, b,					\
-			  (((struct vectorlike_header *)	\
+			  (((union vectorlike_header *)	\
 			    XUNTAG (a, Lisp_Vectorlike))	\
 			   ->size),				\
 			  code)
@@ -1399,7 +1399,7 @@ STRING_SET_CHARS (Lisp_Object string, ptrdiff_t newsize)
 
 struct Lisp_Vector
   {
-    struct vectorlike_header header;
+    union vectorlike_header header;
     Lisp_Object contents[FLEXIBLE_ARRAY_MEMBER];
   };
 
@@ -1456,7 +1456,7 @@ PSEUDOVECTOR_TYPE (struct Lisp_Vector *v)
 
 /* Can't be used with PVEC_NORMAL_VECTOR.  */
 INLINE bool
-PSEUDOVECTOR_TYPEP (struct vectorlike_header *a, enum pvec_type code)
+PSEUDOVECTOR_TYPEP (union vectorlike_header *a, enum pvec_type code)
 {
   /* We don't use PSEUDOVECTOR_TYPE here so as to avoid a shift
    * operation when `code' is known.  */
@@ -1472,8 +1472,8 @@ PSEUDOVECTORP (Lisp_Object a, int code)
     return false;
   else
     {
-      /* Converting to struct vectorlike_header * avoids aliasing issues.  */
-      struct vectorlike_header *h = XUNTAG (a, Lisp_Vectorlike);
+      /* Converting to union vectorlike_header * avoids aliasing issues.  */
+      union vectorlike_header *h = XUNTAG (a, Lisp_Vectorlike);
       return PSEUDOVECTOR_TYPEP (h, code);
     }
 }
@@ -1484,7 +1484,7 @@ struct Lisp_Bool_Vector
   {
     /* HEADER.SIZE is the vector's size field.  It doesn't have the real size,
        just the subtype information.  */
-    struct vectorlike_header header;
+    union vectorlike_header header;
     /* This is the size in bits.  */
     EMACS_INT size;
     /* The actual bits, packed into bytes.
@@ -1697,7 +1697,7 @@ struct Lisp_Char_Table
        pseudovector type information.  It holds the size, too.
        The size counts the defalt, parent, purpose, ascii,
        contents, and extras slots.  */
-    struct vectorlike_header header;
+    union vectorlike_header header;
 
     /* This holds a default value,
        which is used whenever the value for a specific character is nil.  */
@@ -1739,7 +1739,7 @@ struct Lisp_Sub_Char_Table
   {
     /* HEADER.SIZE is the vector's size field, which also holds the
        pseudovector type information.  It holds the size, too.  */
-    struct vectorlike_header header;
+    union vectorlike_header header;
 
     /* Depth of this sub char-table.  It should be 1, 2, or 3.  A sub
        char-table of depth 1 contains 16 elements, and each element
@@ -1814,7 +1814,7 @@ CHAR_TABLE_SET (Lisp_Object ct, int idx, Lisp_Object val)
 
 struct Lisp_Subr
   {
-    struct vectorlike_header header;
+    union vectorlike_header header;
     union {
       Lisp_Object (*a0) (void);
       Lisp_Object (*a1) (Lisp_Object);
@@ -2026,7 +2026,7 @@ struct hash_table_test
 struct Lisp_Hash_Table
 {
   /* This is for Lisp; the hash table code does not refer to it.  */
-  struct vectorlike_header header;
+  union vectorlike_header header;
 
   /* Nil if table is non-weak.  Otherwise a symbol describing the
      weakness of the table.  */
@@ -3929,7 +3929,7 @@ typedef emacs_value (*emacs_subr) (emacs_env *, ptrdiff_t,
 
 struct Lisp_Module_Function
 {
-  struct vectorlike_header header;
+  union vectorlike_header header;
 
   /* Fields traced by GC; these must come first.  */
   Lisp_Object documentation;

src/process.h

@@ -41,7 +41,7 @@ enum { PROCESS_OPEN_FDS = 6 };
 
 struct Lisp_Process
   {
-    struct vectorlike_header header;
+    union vectorlike_header header;
 
     /* Name of subprocess terminal.  */
     Lisp_Object tty_name;

src/termhooks.h

@@ -373,7 +373,7 @@ extern struct tty_display_info *gpm_tty;
 struct terminal
 {
   /* This is for Lisp; the terminal code does not refer to it.  */
-  struct vectorlike_header header;
+  union vectorlike_header header;
 
   /* Parameter alist of this terminal.  */
   Lisp_Object param_alist;

src/thread.h

@@ -35,7 +35,7 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 
 struct thread_state
 {
-  struct vectorlike_header header;
+  union vectorlike_header header;
 
   /* The buffer in which the last search was performed, or
      Qt if the last search was done in a string;
@@ -230,7 +230,7 @@ typedef struct
 /* A mutex as a lisp object.  */
 struct Lisp_Mutex
 {
-  struct vectorlike_header header;
+  union vectorlike_header header;
 
   /* The name of the mutex, or nil.  */
   Lisp_Object name;
@@ -261,7 +261,7 @@ XMUTEX (Lisp_Object a)
 /* A condition variable as a lisp object.  */
 struct Lisp_CondVar
 {
-  struct vectorlike_header header;
+  union vectorlike_header header;
 
   /* The associated mutex.  */
   Lisp_Object mutex;

src/w32term.h

@@ -431,7 +431,7 @@ extern struct w32_output w32term_display;
 struct scroll_bar {
 
   /* This field is shared by all vectors.  */
-  struct vectorlike_header header;
+  union vectorlike_header header;
 
   /* The window we're a scroll bar for.  */
   Lisp_Object window;

src/window.c

@@ -3733,8 +3733,8 @@ make_parent_window (Lisp_Object window, bool horflag)
 
   o = XWINDOW (window);
   p = allocate_window ();
-  memcpy ((char *) p + sizeof (struct vectorlike_header),
-	  (char *) o + sizeof (struct vectorlike_header),
+  memcpy ((char *) p + sizeof (union vectorlike_header),
+	  (char *) o + sizeof (union vectorlike_header),
 	  word_size * VECSIZE (struct window));
   /* P's buffer slot may change from nil to a buffer...  */
   adjust_window_count (p, 1);
@@ -6232,7 +6232,7 @@ from the top of the window.  */)
 
 struct save_window_data
   {
-    struct vectorlike_header header;
+    union vectorlike_header header;
     Lisp_Object selected_frame;
     Lisp_Object current_window;
     Lisp_Object f_current_buffer;
@@ -6260,7 +6260,7 @@ struct save_window_data
 /* This is saved as a Lisp_Vector.  */
 struct saved_window
 {
-  struct vectorlike_header header;
+  union vectorlike_header header;
 
   Lisp_Object window, buffer, start, pointm, old_pointm;
   Lisp_Object pixel_left, pixel_top, pixel_height, pixel_width;

src/window.h

@@ -88,7 +88,7 @@ struct cursor_pos
 struct window
   {
     /* This is for Lisp; the terminal code does not refer to it.  */
-    struct vectorlike_header header;
+    union vectorlike_header header;
 
     /* The frame this window is on.  */
     Lisp_Object frame;

src/xterm.h

@@ -887,7 +887,7 @@ extern void x_mark_frame_dirty (struct frame *f);
 struct scroll_bar
 {
   /* These fields are shared by all vectors.  */
-  struct vectorlike_header header;
+  union vectorlike_header header;
 
   /* The window we're a scroll bar for.  */
   Lisp_Object window;

src/xwidget.h

@@ -33,7 +33,7 @@ struct window;
 
 struct xwidget
 {
-  struct vectorlike_header header;
+  union vectorlike_header header;
 
   /* Auxiliary data.  */
   Lisp_Object plist;
@@ -62,7 +62,7 @@ struct xwidget
 
 struct xwidget_view
 {
-  struct vectorlike_header header;
+  union vectorlike_header header;
   Lisp_Object model;
   Lisp_Object w;