USE_LISP_UNION_TYPE + USE_LSB_TAG cleanup (Bug#11604)

* alloc.c (make_number) [!defined make_number]:
Remove, as lisp.h always defines this now.
(mark_maybe_pointer): Simplify since USE_LSB_TAG is always defined now.
(roundup_size): Verify that it is a power of 2.
* data.c (Fmake_variable_buffer_local, Fmake_local_variable):
* ftfont.c (ftfont_driver): Use LISP_INITIALLY_ZERO.
* lisp.h (USE_LSB_TAG): Allow the builder to compile with
-DUSE_LSB_TAG=0, to override the automatically-selected default.
USE_LSB_TAG now is always defined to be either 0 or 1.
All uses changed.
(union Lisp_Object): Don't worry about WORDS_BIGENDIAN; the
code works fine either way, and efficiency is not a concern here,
as the union type is for debugging, not for production.
(LISP_MAKE_RVALUE, make_number) [USE_LISP_UNION_TYPE]:
Use an inline function on all platforms when using the union type,
since this is simpler and 'static inline' can be used portably
within Emacs now.
(LISP_INITIALLY_ZERO): New macro.
(XFASTINT, XSETFASTINT) [USE_LISP_UNION_TYPE]: Remove.
(XSET) [USE_LISP_UNION_TYPE]: Don't overparenthesize.

9 files changed, 91 insertions, 124 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index cd5c96cf36e..8a32572907d 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,27 @@
+2012-06-13  Paul Eggert  <eggert@cs.ucla.edu>
+
+        USE_LISP_UNION_TYPE + USE_LSB_TAG cleanup (Bug#11604)
+        * alloc.c (make_number) [!defined make_number]:
+        Remove, as lisp.h always defines this now.
+        (mark_maybe_pointer): Simplify since USE_LSB_TAG is always defined now.
+        (roundup_size): Verify that it is a power of 2.
+        * data.c (Fmake_variable_buffer_local, Fmake_local_variable):
+        * ftfont.c (ftfont_driver): Use LISP_INITIALLY_ZERO.
+        * lisp.h (USE_LSB_TAG): Allow the builder to compile with
+        -DUSE_LSB_TAG=0, to override the automatically-selected default.
+        USE_LSB_TAG now is always defined to be either 0 or 1.
+        All uses changed.
+        (union Lisp_Object): Don't worry about WORDS_BIGENDIAN; the
+        code works fine either way, and efficiency is not a concern here,
+        as the union type is for debugging, not for production.
+        (LISP_MAKE_RVALUE, make_number) [USE_LISP_UNION_TYPE]:
+        Use an inline function on all platforms when using the union type,
+        since this is simpler and 'static inline' can be used portably
+        within Emacs now.
+        (LISP_INITIALLY_ZERO): New macro.
+        (XFASTINT, XSETFASTINT) [USE_LISP_UNION_TYPE]: Remove.
+        (XSET) [USE_LISP_UNION_TYPE]: Don't overparenthesize.
+
 2012-06-12  Glenn Morris  <rgm@gnu.org>
 
         * s/gnu-kfreebsd.h, s/hpux11.h, s/openbsd.h, s/sol2-10.h: Remove files.
diff --git a/src/alloc.c b/src/alloc.c
index 7051af9b99c..1223f0bc13d 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -533,7 +533,7 @@ buffer_memory_full (ptrdiff_t nbytes)
     },                                                  \
     c)
 
-#ifdef USE_LSB_TAG
+#if USE_LSB_TAG
 # define XMALLOC_HEADER_ALIGNMENT \
     COMMON_MULTIPLE (1 << GCTYPEBITS, XMALLOC_BASE_ALIGNMENT)
 #else
@@ -893,8 +893,8 @@ safe_alloca_unwind (Lisp_Object arg)
    number of bytes to allocate, TYPE describes the intended use of the
    allocated memory block (for strings, for conses, ...).  */
 
-#ifndef USE_LSB_TAG
-static void *lisp_malloc_loser;
+#if ! USE_LSB_TAG
+void *lisp_malloc_loser EXTERNALLY_VISIBLE;
 #endif
 
 static void *
@@ -910,7 +910,7 @@ lisp_malloc (size_t nbytes, enum mem_type type)
 
   val = (void *) malloc (nbytes);
 
-#ifndef USE_LSB_TAG
+#if ! USE_LSB_TAG
   /* If the memory just allocated cannot be addressed thru a Lisp
      object's pointer, and it needs to be,
      that's equivalent to running out of memory.  */
@@ -1091,7 +1091,7 @@ lisp_align_malloc (size_t nbytes, enum mem_type type)
       mallopt (M_MMAP_MAX, MMAP_MAX_AREAS);
 #endif
 
-#ifndef USE_LSB_TAG
+#if ! USE_LSB_TAG
       /* If the memory just allocated cannot be addressed thru a Lisp
          object's pointer, and it needs to be, that's equivalent to
          running out of memory.  */
@@ -1584,20 +1584,6 @@ mark_interval_tree (register INTERVAL tree)
    if (! NULL_INTERVAL_P (i))                           \
      (i) = balance_intervals (i);                       \
   } while (0)
-
-
-/* Number support.  If USE_LISP_UNION_TYPE is in effect, we
-   can't create number objects in macros.  */
-#ifndef make_number
-Lisp_Object
-make_number (EMACS_INT n)
-{
-  Lisp_Object obj;
-  obj.s.val = n;
-  obj.s.type = Lisp_Int;
-  return obj;
-}
-#endif
 
 /* Convert the pointer-sized word P to EMACS_INT while preserving its
    type and ptr fields.  */
@@ -2943,18 +2929,13 @@ enum
     header_size = offsetof (struct Lisp_Vector, contents),
     word_size = sizeof (Lisp_Object),
     roundup_size = COMMON_MULTIPLE (sizeof (Lisp_Object),
-#ifdef USE_LSB_TAG
-    8 /* Helps to maintain alignment constraints imposed by
-         assumption that least 3 bits of pointers are always 0.  */
-#else
-    1 /* If alignment doesn't matter, should round up
-         to sizeof (Lisp_Object) at least.  */
-#endif
-    )
+                                    USE_LSB_TAG ? 1 << GCTYPEBITS : 1)
   };
 
-/* Round up X to nearest mult-of-ROUNDUP_SIZE,
-   assuming ROUNDUP_SIZE is a power of 2.  */
+/* ROUNDUP_SIZE must be a power of 2.  */
+verify ((roundup_size & (roundup_size - 1)) == 0);
+
+/* Round up X to nearest mult-of-ROUNDUP_SIZE.  */
 
 #define vroundup(x) (((x) + (roundup_size - 1)) & ~(roundup_size - 1))
 
@@ -3171,7 +3152,7 @@ sweep_vectors (void)
                   == VECTOR_FREE_LIST_FLAG)
                 vector->header.next.nbytes =
                   vector->header.size & (VECTOR_BLOCK_SIZE - 1);
-              
+
               next = ADVANCE (vector, vector->header.next.nbytes);
 
               /* While NEXT is not marked, try to coalesce with VECTOR,
@@ -3189,7 +3170,7 @@ sweep_vectors (void)
                   vector->header.next.nbytes += nbytes;
                   next = ADVANCE (next, nbytes);
                 }
-              
+
               eassert (vector->header.next.nbytes % roundup_size == 0);
 
               if (vector == (struct Lisp_Vector *) block->data
@@ -3468,7 +3449,7 @@ usage: (make-byte-code ARGLIST BYTE-CODE CONSTANTS DEPTH &optional DOCSTRING INT
 union aligned_Lisp_Symbol
 {
   struct Lisp_Symbol s;
-#ifdef USE_LSB_TAG
+#if USE_LSB_TAG
   unsigned char c[(sizeof (struct Lisp_Symbol) + (1 << GCTYPEBITS) - 1)
                   & -(1 << GCTYPEBITS)];
 #endif
@@ -3574,7 +3555,7 @@ Its value and function definition are void, and its property list is nil.  */)
 union aligned_Lisp_Misc
 {
   union Lisp_Misc m;
-#ifdef USE_LSB_TAG
+#if USE_LSB_TAG
   unsigned char c[(sizeof (union Lisp_Misc) + (1 << GCTYPEBITS) - 1)
                   & -(1 << GCTYPEBITS)];
 #endif
@@ -4556,14 +4537,10 @@ mark_maybe_pointer (void *p)
 {
   struct mem_node *m;
 
-  /* Quickly rule out some values which can't point to Lisp data.  */
-  if ((intptr_t) p %
-#ifdef USE_LSB_TAG
-      8 /* USE_LSB_TAG needs Lisp data to be aligned on multiples of 8.  */
-#else
-      2 /* We assume that Lisp data is aligned on even addresses.  */
-#endif
-      )
+  /* Quickly rule out some values which can't point to Lisp data.
+     USE_LSB_TAG needs Lisp data to be aligned on multiples of 1 << GCTYPEBITS.
+     Otherwise, assume that Lisp data is aligned on even addresses.  */
+  if ((intptr_t) p % (USE_LSB_TAG ? 1 << GCTYPEBITS : 2))
     return;
 
   m = mem_find (p);
@@ -4639,8 +4616,8 @@ mark_maybe_pointer (void *p)
    wider than a pointer might allocate a Lisp_Object in non-adjacent halves.
    If USE_LSB_TAG, the bottom half is not a valid pointer, but it should
    suffice to widen it to to a Lisp_Object and check it that way.  */
-#if defined USE_LSB_TAG || VAL_MAX < UINTPTR_MAX
-# if !defined USE_LSB_TAG && VAL_MAX < UINTPTR_MAX >> GCTYPEBITS
+#if USE_LSB_TAG || VAL_MAX < UINTPTR_MAX
+# if !USE_LSB_TAG && VAL_MAX < UINTPTR_MAX >> GCTYPEBITS
   /* If tag bits straddle pointer-word boundaries, neither mark_maybe_pointer
      nor mark_maybe_object can follow the pointers.  This should not occur on
      any practical porting target.  */
@@ -5069,7 +5046,7 @@ static void *
 pure_alloc (size_t size, int type)
 {
   void *result;
-#ifdef USE_LSB_TAG
+#if USE_LSB_TAG
   size_t alignment = (1 << GCTYPEBITS);
 #else
   size_t alignment = sizeof (EMACS_INT);
diff --git a/src/data.c b/src/data.c
index defcd06a2ed..4449977dbe0 100644
--- a/src/data.c
+++ b/src/data.c
@@ -1500,7 +1500,7 @@ The function `default-value' gets the default value and `set-default' sets it.
 {
   struct Lisp_Symbol *sym;
   struct Lisp_Buffer_Local_Value *blv = NULL;
-  union Lisp_Val_Fwd valcontents IF_LINT (= {0});
+  union Lisp_Val_Fwd valcontents IF_LINT (= {LISP_INITIALLY_ZERO});
   int forwarded IF_LINT (= 0);
 
   CHECK_SYMBOL (variable);
@@ -1577,7 +1577,7 @@ Instead, use `add-hook' and specify t for the LOCAL argument.  */)
 {
   register Lisp_Object tem;
   int forwarded IF_LINT (= 0);
-  union Lisp_Val_Fwd valcontents IF_LINT (= {0});
+  union Lisp_Val_Fwd valcontents IF_LINT (= {LISP_INITIALLY_ZERO});
   struct Lisp_Symbol *sym;
   struct Lisp_Buffer_Local_Value *blv = NULL;
 
diff --git a/src/emacs.c b/src/emacs.c
index 8ffacdab1c6..bc3f918e2af 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -104,7 +104,7 @@ static const char emacs_copyright[] = "Copyright (C) 2012 Free Software Foundati
 
 /* Make these values available in GDB, which doesn't see macros.  */
 
-#ifdef USE_LSB_TAG
+#if USE_LSB_TAG
 int gdb_use_lsb EXTERNALLY_VISIBLE = 1;
 #else
 int gdb_use_lsb EXTERNALLY_VISIBLE = 0;
@@ -116,7 +116,7 @@ int gdb_use_union EXTERNALLY_VISIBLE = 1;
 #endif
 int gdb_valbits EXTERNALLY_VISIBLE = VALBITS;
 int gdb_gctypebits EXTERNALLY_VISIBLE = GCTYPEBITS;
-#if defined (DATA_SEG_BITS) && ! defined (USE_LSB_TAG)
+#if defined DATA_SEG_BITS && !USE_LSB_TAG
 uintptr_t gdb_data_seg_bits EXTERNALLY_VISIBLE = DATA_SEG_BITS;
 #else
 uintptr_t gdb_data_seg_bits EXTERNALLY_VISIBLE = 0;
diff --git a/src/ftfont.c b/src/ftfont.c
index 5545b4b4ae2..bfce7425af4 100644
--- a/src/ftfont.c
+++ b/src/ftfont.c
@@ -525,7 +525,7 @@ static int ftfont_variation_glyphs (struct font *, int c,
 
 struct font_driver ftfont_driver =
   {
-    0,                          /* Qfreetype */
+    LISP_INITIALLY_ZERO,        /* Qfreetype */
     0,                          /* case insensitive */
     ftfont_get_cache,
     ftfont_list,
diff --git a/src/lisp.h b/src/lisp.h
index 9e108d950d3..0e9b0c63c7f 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -161,10 +161,8 @@ extern int suppress_checking EXTERNALLY_VISIBLE;
      always 0, and we can thus use them to hold tag bits, without
      restricting our addressing space.
 
-   If USE_LSB_TAG is not set, then we use the top 3 bits for tagging, thus
-   restricting our possible address range.  Currently USE_LSB_TAG is not
-   allowed together with a union.  This is not due to any fundamental
-   technical (or political ;-) problem: nobody wrote the code to do it yet.
+   If ! USE_LSB_TAG, then use the top 3 bits for tagging, thus
+   restricting our possible address range.
 
    USE_LSB_TAG not only requires the least 3 bits of pointers returned by
    malloc to be 0 but also needs to be able to impose a mult-of-8 alignment
@@ -201,25 +199,31 @@ extern int suppress_checking EXTERNALLY_VISIBLE;
 # endif
 #endif
 
-/* Let's USE_LSB_TAG on systems where we know malloc returns mult-of-8.  */
-#if (defined GNU_MALLOC || defined DOUG_LEA_MALLOC || defined __GLIBC__ \
-     || defined DARWIN_OS || defined __sun)
-/* We also need to be able to specify mult-of-8 alignment on static vars.  */
-# if defined DECL_ALIGN
-/* On hosts where pointers-as-ints do not exceed VAL_MAX,
-   USE_LSB_TAG is:
+/* Unless otherwise specified, use USE_LSB_TAG on systems where:  */
+#ifndef USE_LSB_TAG
+/* 1.  We know malloc returns a multiple of 8.  */
+# if (defined GNU_MALLOC || defined DOUG_LEA_MALLOC || defined __GLIBC__ \
+      || defined DARWIN_OS || defined __sun)
+/* 2.  We can specify multiple-of-8 alignment on static variables.  */
+#  ifdef DECL_ALIGN
+/* 3.  Pointers-as-ints exceed VAL_MAX.
+   On hosts where pointers-as-ints do not exceed VAL_MAX, USE_LSB_TAG is:
     a. unnecessary, because the top bits of an EMACS_INT are unused, and
     b. slower, because it typically requires extra masking.
-   So, define USE_LSB_TAG only on hosts where it might be useful.  */
-#  if VAL_MAX < UINTPTR_MAX
-#   define USE_LSB_TAG
+   So, default USE_LSB_TAG to 1 only on hosts where it might be useful.  */
+#   if VAL_MAX < UINTPTR_MAX
+#    define USE_LSB_TAG 1
+#   endif
 #  endif
 # endif
 #endif
+#ifndef USE_LSB_TAG
+# define USE_LSB_TAG 0
+#endif
 
 /* If we cannot use 8-byte alignment, make DECL_ALIGN a no-op.  */
 #ifndef DECL_ALIGN
-# ifdef USE_LSB_TAG
+# if USE_LSB_TAG
 #  error "USE_LSB_TAG used without defining DECL_ALIGN"
 # endif
 # define DECL_ALIGN(type, var) type var
@@ -248,7 +252,7 @@ extern int suppress_checking EXTERNALLY_VISIBLE;
 #else
 # define LISP_INT_TAG Lisp_Int0
 # define case_Lisp_Int case Lisp_Int0: case Lisp_Int1
-# ifdef USE_LSB_TAG
+# if USE_LSB_TAG
 #  define LISP_INT1_TAG 4
 #  define LISP_STRING_TAG 1
 #  define LISP_INT_TAG_P(x) (((x) & 3) == 0)
@@ -333,10 +337,6 @@ enum Lisp_Fwd_Type
 
 #ifdef USE_LISP_UNION_TYPE
 
-#ifndef WORDS_BIGENDIAN
-
-/* Definition of Lisp_Object for little-endian machines.  */
-
 typedef
 union Lisp_Object
   {
@@ -359,44 +359,13 @@ union Lisp_Object
   }
 Lisp_Object;
 
-#else /* If WORDS_BIGENDIAN */
-
-typedef
-union Lisp_Object
-  {
-    /* Used for comparing two Lisp_Objects;
-       also, positive integers can be accessed fast this way.  */
-    EMACS_INT i;
-
-    struct
-      {
-        ENUM_BF (Lisp_Type) type : GCTYPEBITS;
-        /* Use explicit signed, the signedness of a bit-field of type
-           int is implementation defined.  */
-        signed EMACS_INT val  : VALBITS;
-      } s;
-    struct
-      {
-        ENUM_BF (Lisp_Type) type : GCTYPEBITS;
-        EMACS_UINT val : VALBITS;
-      } u;
-  }
-Lisp_Object;
-
-#endif /* WORDS_BIGENDIAN */
-
-#ifdef __GNUC__
 static inline Lisp_Object
 LISP_MAKE_RVALUE (Lisp_Object o)
 {
     return o;
 }
-#else
-/* This is more portable to pre-C99 non-GCC compilers, but for
-   backwards compatibility GCC still accepts an old GNU extension
-   which caused this to only generate a warning.  */
-#define LISP_MAKE_RVALUE(o) (0 ? (o) : (o))
-#endif
+
+#define LISP_INITIALLY_ZERO {0}
 
 #else /* USE_LISP_UNION_TYPE */
 
@@ -404,6 +373,7 @@ LISP_MAKE_RVALUE (Lisp_Object o)
 
 typedef EMACS_INT Lisp_Object;
 #define LISP_MAKE_RVALUE(o) (0+(o))
+#define LISP_INITIALLY_ZERO 0
 #endif /* USE_LISP_UNION_TYPE */
 
 /* In the size word of a vector, this bit means the vector has been marked.  */
@@ -467,7 +437,7 @@ enum pvec_type
 /* Return a perfect hash of the Lisp_Object representation.  */
 #define XHASH(a) (a)
 
-#ifdef USE_LSB_TAG
+#if USE_LSB_TAG
 
 #define TYPEMASK ((((EMACS_INT) 1) << GCTYPEBITS) - 1)
 #define XTYPE(a) ((enum Lisp_Type) ((a) & TYPEMASK))
@@ -542,12 +512,12 @@ enum pvec_type
 #define XINT(a) ((EMACS_INT) (a).s.val)
 #define XUINT(a) ((EMACS_UINT) (a).u.val)
 
-#ifdef USE_LSB_TAG
+#if USE_LSB_TAG
 
 # define XSET(var, vartype, ptr) \
-  (eassert ((((uintptr_t) (ptr)) & ((1 << GCTYPEBITS) - 1)) == 0),      \
-   (var).u.val = ((uintptr_t) (ptr)) >> GCTYPEBITS,                     \
-   (var).u.type = ((char) (vartype)))
+  (eassert (((uintptr_t) (ptr) & ((1 << GCTYPEBITS) - 1)) == 0),        \
+   (var).u.val = (uintptr_t) (ptr) >> GCTYPEBITS,                       \
+   (var).u.type = (vartype))
 
 /* Some versions of gcc seem to consider the bitfield width when issuing
    the "cast to pointer from integer of different size" warning, so the
@@ -556,14 +526,8 @@ enum pvec_type
 
 #else  /* !USE_LSB_TAG */
 
-/* For integers known to be positive, XFASTINT provides fast retrieval
-   and XSETFASTINT provides fast storage.  This takes advantage of the
-   fact that Lisp_Int is 0.  */
-# define XFASTINT(a) ((a).i + 0)
-# define XSETFASTINT(a, b) ((a).i = (b))
-
 # define XSET(var, vartype, ptr) \
-   (((var).s.val = ((intptr_t) (ptr))), ((var).s.type = ((char) (vartype))))
+   ((var).s.val = (intptr_t) (ptr), (var).s.type = (vartype))
 
 #ifdef DATA_SEG_BITS
 /* DATA_SEG_BITS forces extra bits to be or'd in with any pointers
@@ -575,12 +539,14 @@ enum pvec_type
 
 #endif  /* !USE_LSB_TAG */
 
-#if __GNUC__ >= 2 && defined (__OPTIMIZE__)
-#define make_number(N) \
-  (__extension__ ({ Lisp_Object _l; _l.s.val = (N); _l.s.type = Lisp_Int; _l; }))
-#else
-extern Lisp_Object make_number (EMACS_INT);
-#endif
+static inline Lisp_Object
+make_number (EMACS_INT n)
+{
+  Lisp_Object o;
+  o.s.val = n;
+  o.s.type = Lisp_Int;
+  return o;
+}
 
 #endif /* USE_LISP_UNION_TYPE */
 
diff --git a/src/mem-limits.h b/src/mem-limits.h
index 1fd53b472f3..01b0e6ebb2b 100644
--- a/src/mem-limits.h
+++ b/src/mem-limits.h
@@ -34,7 +34,7 @@ extern int etext;
 #endif
 
 extern char *start_of_data (void);
-#if defined USE_LSB_TAG || UINTPTR_MAX <= VAL_MAX
+#if USE_LSB_TAG || UINTPTR_MAX <= VAL_MAX
 #define EXCEEDS_LISP_PTR(ptr) 0
 #elif defined DATA_SEG_BITS
 #define EXCEEDS_LISP_PTR(ptr) \
diff --git a/src/w32heap.c b/src/w32heap.c
index da8579896f2..00572b20ae9 100644
--- a/src/w32heap.c
+++ b/src/w32heap.c
@@ -114,7 +114,7 @@ get_data_end (void)
   return data_region_end;
 }
 
-#if !defined (USE_LISP_UNION_TYPE) && !defined (USE_LSB_TAG)
+#if !defined USE_LISP_UNION_TYPE && !USE_LSB_TAG
 static char *
 allocate_heap (void)
 {
@@ -259,7 +259,7 @@ init_heap (void)
           exit (1);
         }
 
-#if !defined (USE_LISP_UNION_TYPE) && !defined (USE_LSB_TAG)
+#if !defined USE_LISP_UNION_TYPE && !USE_LSB_TAG
       /* Ensure that the addresses don't use the upper tag bits since
          the Lisp type goes there.  */
       if (((unsigned long) data_region_base & ~VALMASK) != 0)
diff --git a/src/xfont.c b/src/xfont.c
index bde76c0ba3c..cc06e27fe02 100644
--- a/src/xfont.c
+++ b/src/xfont.c
@@ -132,7 +132,7 @@ static int xfont_check (FRAME_PTR, struct font *);
 
 struct font_driver xfont_driver =
   {
-    0,                          /* Qx */
+    LISP_INITIALLY_ZERO,        /* Qx */
     0,                          /* case insensitive */
     xfont_get_cache,
     xfont_list,