Backport revisions 2011-04-24T05:30:24Z!eggert@cs.ucla.edu..2011-04-25T19:40:22Z!eggert@cs.ucla.edu (inclusive) from trunk (bug#8623)

	The next log entry shows the actual changes by Paul Eggert.

 Fix a problem with aliasing and vector headers.
 GCC 4.6.0 optimizes based on type-based alias analysis.  For
 example, if b is of type struct buffer * and v of type struct
 Lisp_Vector *, then gcc -O2 was incorrectly assuming that &b->size
 != &v->size, and therefore "v->size = 1; b->size = 2; return
 v->size;" must therefore return 1.  This assumption is incorrect
 for Emacs, since it type-puns struct Lisp_Vector * with many other
 types.  To fix this problem, this patch adds a new type struct
 vector_header that documents the constraints on layout of vectors
 and pseudovectors, and helps optimizing compilers not get fooled
 by Emacs's type punning.  It also adds the macros XSETTYPED_PVECTYPE
 XSETTYPED_PSEUDOVECTOR, TYPED_PSEUDOVECTORP, for similar reasons.
 src/lisp.h (XVECTOR_SIZE): New convenience macro.  All previous uses of
 XVECTOR (foo)->size replaced to use this macro, to avoid the hassle
 of writing XVECTOR (foo)->header.size.
 src/lisp.h: Say "vectorlike header" rather than "vector header.
 (struct vectorlike_header): Rename from struct vector_header.
 (XVECTORLIKE_HEADER_SIZE): Renamed from XVECTOR_HEADER_SIZE.
 All uses changed.
 (XVECTOR_HEADER_SIZE): New macro, for use in XSETPSEUDOVECTOR.
 (XSETTYPED_PVECTYPE): New macro, specifying the name of the size
 member.
 (XSETPVECTYPE): Rewrite in terms of new macro.
 (XSETPVECTYPESIZE): New macro, specifying both type and size.
 This is a bit clearer, and further avoids the possibility of
 undesirable aliasing.
 (XSETTYPED_PSEUDOVECTOR): New macro, specifying the size.
 (XSETPSEUDOVECTOR): Rewrite in terms of XSETTYPED_PSEUDOVECTOR
 and XVECTOR_HEADER_SIZE.
 (XSETSUBR): Rewrite in terms of XSETTYPED_PSEUDOVECTOR and XSIZE,
 since Lisp_Subr is a special case (no "next" field).
 (ASIZE): Rewrite in terms of XVECTOR_SIZE.
 (struct vector_header): New type.
 (TYPED_PSEUDOVECTORP): New macro, also specifying the C type of the
 object, to help avoid aliasing.
 (PSEUDOVECTORP): Rewrite in terms of TYPED_PSEUDOVECTORP.
 (SUBRP): Likewise, since Lisp_Subr is a special case.
 src/lisp.h (struct Lisp_Vector, struct Lisp_Char_Table):
 (struct Lisp_Sub_Char_Table, struct Lisp_Bool_Vector):
 (struct Lisp_Hash_Table): Combine first two members into a single
 struct vector_header member.  All uses of "size" and "next" members
 changed to be "header.size" and "header.next".
 src/buffer.h (struct buffer): Likewise.
 src/font.h (struct font_spec, struct font_entity, struct font): Likewise.
 src/frame.h (struct frame): Likewise.
 src/process.h (struct Lisp_Process): Likewise.
 src/termhooks.h (struct terminal): Likewise.
 src/window.c (struct save_window_data, struct saved_window): Likewise.
 src/window.h (struct window): Likewise.
 src/alloc.c (allocate_buffer, Fmake_bool_vector, allocate_pseudovector):
 Use XSETPVECTYPESIZE, not XSETPVECTYPE, to avoid aliasing problems.
 src/buffer.c (init_buffer_once): Likewise.
 src/lread.c (defsubr): Use XSETTYPED_PVECTYPE, since Lisp_Subr is a
 special case.
 src/process.c (Fformat_network_address): Use local var for size,
 for brevity.
 src/fns.c (vector): Remove; this old hack is no longer needed.
 src/bytecode.c (exec_byte_code): Don't use XVECTOR before CHECK_VECTOR.

1 files changed, 9 insertions, 7 deletions

diff --git a/src/xmenu.c b/src/xmenu.c
index c2e70e13bf9..2a05c52ee34 100644
--- a/src/xmenu.c
+++ b/src/xmenu.c
@@ -1012,6 +1012,7 @@ set_frame_menubar (f, first_time, deep_p)
       Lisp_Object *previous_items
 	= (Lisp_Object *) alloca (previous_menu_items_used
 				  * sizeof (Lisp_Object));
+      EMACS_UINT subitems;
 
       /* If we are making a new widget, its contents are empty,
 	 do always reinitialize them.  */
@@ -1056,13 +1057,14 @@ set_frame_menubar (f, first_time, deep_p)
 
       menu_items = f->menu_bar_vector;
       menu_items_allocated = VECTORP (menu_items) ? ASIZE (menu_items) : 0;
-      submenu_start = (int *) alloca (XVECTOR (items)->size * sizeof (int *));
-      submenu_end = (int *) alloca (XVECTOR (items)->size * sizeof (int *));
-      submenu_n_panes = (int *) alloca (XVECTOR (items)->size * sizeof (int));
+      subitems = XVECTOR_SIZE (items) / 4;
+      submenu_start = (int *) alloca (subitems * sizeof (int *));
+      submenu_end = (int *) alloca (subitems * sizeof (int *));
+      submenu_n_panes = (int *) alloca (subitems * sizeof (int));
       submenu_top_level_items
-	= (int *) alloca (XVECTOR (items)->size * sizeof (int *));
+	= (int *) alloca (subitems * sizeof (int *));
       init_menu_items ();
-      for (i = 0; i < XVECTOR (items)->size; i += 4)
+      for (i = 0; i < subitems; i += 4)
 	{
 	  Lisp_Object key, string, maps;
 
@@ -1142,7 +1144,7 @@ set_frame_menubar (f, first_time, deep_p)
       /* Now GC cannot happen during the lifetime of the widget_value,
 	 so it's safe to store data from a Lisp_String.  */
       wv = first_wv->contents;
-      for (i = 0; i < XVECTOR (items)->size; i += 4)
+      for (i = 0; i < XVECTOR_SIZE (items); i += 4)
 	{
 	  Lisp_Object string;
 	  string = XVECTOR (items)->contents[i + 1];
@@ -1168,7 +1170,7 @@ set_frame_menubar (f, first_time, deep_p)
       first_wv = wv;
 
       items = FRAME_MENU_BAR_ITEMS (f);
-      for (i = 0; i < XVECTOR (items)->size; i += 4)
+      for (i = 0; i < XVECTOR_SIZE (items); i += 4)
 	{
 	  Lisp_Object string;