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, 5 insertions, 9 deletions

diff --git a/src/window.c b/src/window.c
index 3e6062a7153..894ff65b600 100644
--- a/src/window.c
+++ b/src/window.c
@@ -5931,8 +5931,7 @@ zero means top of window, negative means relative to bottom of window.  */)
 
 struct save_window_data
   {
-    EMACS_UINT size;
-    struct Lisp_Vector *next_from_Lisp_Vector_struct;
+    struct vectorlike_header header;
     Lisp_Object selected_frame;
     Lisp_Object current_window;
     Lisp_Object current_buffer;
@@ -5954,10 +5953,7 @@ struct save_window_data
 /* This is saved as a Lisp_Vector  */
 struct saved_window
 {
-  /* these first two must agree with struct Lisp_Vector in lisp.h */
-  EMACS_UINT size;
-  struct Lisp_Vector *next_from_Lisp_Vector_struct;
-
+  struct vectorlike_header header;
   Lisp_Object window;
   Lisp_Object buffer, start, pointm, mark;
   Lisp_Object left_col, top_line, total_cols, total_lines;
@@ -6141,7 +6137,7 @@ the return value is nil.  Otherwise the value is t.  */)
          dead.  */
       delete_all_subwindows (XWINDOW (FRAME_ROOT_WINDOW (f)));
 
-      for (k = 0; k < saved_windows->size; k++)
+      for (k = 0; k < saved_windows->header.size; k++)
         {
           p = SAVED_WINDOW_N (saved_windows, k);
           w = XWINDOW (p->window);
@@ -7078,10 +7074,10 @@ compare_window_configurations (c1, c2, ignore_positions)
     return 0;
 
   /* Verify that the two confis have the same number of windows.  */
-  if (sw1->size != sw2->size)
+  if (sw1->header.size != sw2->header.size)
     return 0;
 
-  for (i = 0; i < sw1->size; i++)
+  for (i = 0; i < sw1->header.size; i++)
     {
       struct saved_window *p1, *p2;
       int w1_is_current, w2_is_current;