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, 8 insertions, 7 deletions

diff --git a/src/process.c b/src/process.c
index 9a33500dc4e..d4371fb8f32 100644
--- a/src/process.c
+++ b/src/process.c
@@ -1277,25 +1277,26 @@ Returns nil if format of ADDRESS is invalid.  */)
   if (VECTORP (address))  /* AF_INET or AF_INET6 */
     {
       register struct Lisp_Vector *p = XVECTOR (address);
+      EMACS_UINT size = p->header.size;
       Lisp_Object args[10];
       int nargs, i;
 
-      if (p->size == 4 || (p->size == 5 && !NILP (omit_port)))
+      if (size == 4 || (size == 5 && !NILP (omit_port)))
         {
           args[0] = build_string ("%d.%d.%d.%d");
           nargs = 4;
         }
-      else if (p->size == 5)
+      else if (size == 5)
         {
           args[0] = build_string ("%d.%d.%d.%d:%d");
           nargs = 5;
         }
-      else if (p->size == 8 || (p->size == 9 && !NILP (omit_port)))
+      else if (size == 8 || (size == 9 && !NILP (omit_port)))
         {
           args[0] = build_string ("%x:%x:%x:%x:%x:%x:%x:%x");
           nargs = 8;
         }
-      else if (p->size == 9)
+      else if (size == 9)
         {
           args[0] = build_string ("[%x:%x:%x:%x:%x:%x:%x:%x]:%d");
           nargs = 9;
@@ -2477,13 +2478,13 @@ get_lisp_to_sockaddr_size (address, familyp)
   if (VECTORP (address))
     {
       p = XVECTOR (address);
-      if (p->size == 5)
+      if (p->header.size == 5)
         {
           *familyp = AF_INET;
           return sizeof (struct sockaddr_in);
         }
 #ifdef AF_INET6
-      else if (p->size == 9)
+      else if (p->header.size == 9)
         {
           *familyp = AF_INET6;
           return sizeof (struct sockaddr_in6);
@@ -2502,7 +2503,7 @@ get_lisp_to_sockaddr_size (address, familyp)
       struct sockaddr *sa;
       *familyp = XINT (XCAR (address));
       p = XVECTOR (XCDR (address));
-      return p->size + sizeof (sa->sa_family);
+      return p->header.size + sizeof (sa->sa_family);
     }
   return 0;
 }