Port to C compilers that lack size-0 arrays

The C standard does not allow size-zero arrays, so redo struct
Lisp_Subr to not use size-zero arrays when native compilation is
not being used.  Formerly, the code was using size-zero arrays (a
GNU C extension) to avoid using memory unnecessarily when
HAVE_NATIVE_COMP is not defined.  Replace this hack with the
more-traditional hack of putting the relevant members inside
‘#ifdef HAVE_NATIVE_COMP’.
* src/alloc.c (cleanup_vector, mark_object):
* src/comp.c (make_subr):
* src/data.c (Fsubr_native_lambda_list, Fsubr_native_comp_unit):
* src/eval.c (init_eval_once, funcall_lambda):
* src/lisp.h (SUBR_NATIVE_COMPILEDP, SUBR_NATIVE_COMPILED_DYNP)
(SUBR_TYPE):
* src/lread.c (Fload):
Conditionally compile with ‘#ifdef HAVE_NATIVE_COMP’ instead of
with ‘if (NATIVE_COMP_FLAG)’.  Redo members like native_comp_u[0]
to be plain native_comp_u.  Put all uses of these members inside
‘#ifdef HAVE_NATIVE_COMP’.
* src/lisp.h (struct Lisp_Subr): Members native_comp_u,
native_c_name, lambda_list, type are now all ifdeffed out if
HAVE_NATIVE_COMP is not defined, instead of being size-zero
arrays.  All uses changed.
* src/pdumper.c (dump_subr, dump_cold_native_subr)
(dump_do_dump_relocation):
* src/comp.h (NATIVE_COMP_FLAG): Remove; no longer needed.

src/alloc.c

@@ -3152,26 +3152,26 @@ cleanup_vector (struct Lisp_Vector *vector)
       module_finalize_function (function);
     }
 #endif
-  else if (NATIVE_COMP_FLAG
+#ifdef HAVE_NATIVE_COMP
-	   && PSEUDOVECTOR_TYPEP (&vector->header, PVEC_NATIVE_COMP_UNIT))
+  else if (PSEUDOVECTOR_TYPEP (&vector->header, PVEC_NATIVE_COMP_UNIT))
     {
       struct Lisp_Native_Comp_Unit *cu =
 	PSEUDOVEC_STRUCT (vector, Lisp_Native_Comp_Unit);
       unload_comp_unit (cu);
     }
-  else if (NATIVE_COMP_FLAG
+  else if (PSEUDOVECTOR_TYPEP (&vector->header, PVEC_SUBR))
-	   && PSEUDOVECTOR_TYPEP (&vector->header, PVEC_SUBR))
     {
       struct Lisp_Subr *subr =
 	PSEUDOVEC_STRUCT (vector, Lisp_Subr);
-      if (!NILP (subr->native_comp_u[0]))
+      if (!NILP (subr->native_comp_u))
 	{
 	  /* FIXME Alternative and non invasive solution to this
 	     cast?  */
 	  xfree ((char *)subr->symbol_name);
-	  xfree (subr->native_c_name[0]);
+	  xfree (subr->native_c_name);
 	}
     }
+#endif
 }
 
 /* Reclaim space used by unmarked vectors.  */
@@ -6773,15 +6773,17 @@ mark_object (Lisp_Object arg)
 	    break;
 
 	  case PVEC_SUBR:
+#ifdef HAVE_NATIVE_COMP
 	    if (SUBR_NATIVE_COMPILEDP (obj))
 	      {
 		set_vector_marked (ptr);
 		struct Lisp_Subr *subr = XSUBR (obj);
 		mark_object (subr->native_intspec);
-		mark_object (subr->native_comp_u[0]);
+		mark_object (subr->native_comp_u);
-		mark_object (subr->lambda_list[0]);
+		mark_object (subr->lambda_list);
-		mark_object (subr->type[0]);
+		mark_object (subr->type);
 	      }
+#endif
 	    break;
 
 	  case PVEC_FREE:

src/comp.c

@@ -5154,21 +5154,29 @@ make_subr (Lisp_Object symbol_name, Lisp_Object minarg, Lisp_Object maxarg,
   if (CONSP (minarg))
     {
       /* Dynamic code.  */
-      x->s.lambda_list[0] = maxarg;
+#ifdef HAVE_NATIVE_COMP
+      x->s.lambda_list = maxarg;
+#endif
       maxarg = XCDR (minarg);
       minarg = XCAR (minarg);
     }
   else
-    x->s.lambda_list[0] = Qnil;
+    {
+#ifdef HAVE_NATIVE_COMP
+      x->s.lambda_list = Qnil;
+#endif
+    }
   x->s.function.a0 = func;
   x->s.min_args = XFIXNUM (minarg);
   x->s.max_args = FIXNUMP (maxarg) ? XFIXNUM (maxarg) : MANY;
   x->s.symbol_name = xstrdup (SSDATA (symbol_name));
   x->s.native_intspec = intspec;
   x->s.doc = XFIXNUM (doc_idx);
-  x->s.native_comp_u[0] = comp_u;
+#ifdef HAVE_NATIVE_COMP
-  x->s.native_c_name[0] = xstrdup (SSDATA (c_name));
+  x->s.native_comp_u = comp_u;
-  x->s.type[0] = type;
+  x->s.native_c_name = xstrdup (SSDATA (c_name));
+  x->s.type = type;
+#endif
   Lisp_Object tem;
   XSETSUBR (tem, &x->s);
 

src/comp.h

@@ -20,16 +20,6 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #ifndef COMP_H
 #define COMP_H
 
-/* To keep ifdefs under control.  */
-enum {
-  NATIVE_COMP_FLAG =
-#ifdef HAVE_NATIVE_COMP
-  1
-#else
-  0
-#endif
-};
-
 #include <dynlib.h>
 
 struct Lisp_Native_Comp_Unit

src/data.c

@@ -891,9 +891,11 @@ function or t otherwise.  */)
 {
   CHECK_SUBR (subr);
 
-  return SUBR_NATIVE_COMPILED_DYNP (subr)
+#ifdef HAVE_NATIVE_COMP
-    ? XSUBR (subr)->lambda_list[0]
+  if (SUBR_NATIVE_COMPILED_DYNP (subr))
-    : Qt;
+    return XSUBR (subr)->lambda_list;
+#endif
+  return Qt;
 }
 
 DEFUN ("subr-type", Fsubr_type,
@@ -917,7 +919,7 @@ DEFUN ("subr-native-comp-unit", Fsubr_native_comp_unit,
   (Lisp_Object subr)
 {
   CHECK_SUBR (subr);
-  return XSUBR (subr)->native_comp_u[0];
+  return XSUBR (subr)->native_comp_u;
 }
 
 DEFUN ("native-comp-unit-file", Fnative_comp_unit_file,

src/eval.c

@@ -219,17 +219,14 @@ void
 init_eval_once (void)
 {
   /* Don't forget to update docs (lispref node "Local Variables").  */
-  if (!NATIVE_COMP_FLAG)
+#ifndef HAVE_NATIVE_COMP
-    {
   max_specpdl_size = 1800; /* See bug#46818.  */
   max_lisp_eval_depth = 800;
-    }
+#else
-  else
-    {
   /* Original values increased for comp.el.  */
   max_specpdl_size = 2500;
   max_lisp_eval_depth = 1600;
-    }
+#endif
   Vrun_hooks = Qnil;
   pdumper_do_now_and_after_load (init_eval_once_for_pdumper);
 }
@@ -3236,11 +3233,13 @@ funcall_lambda (Lisp_Object fun, ptrdiff_t nargs,
   else if (MODULE_FUNCTIONP (fun))
     return funcall_module (fun, nargs, arg_vector);
 #endif
+#ifdef HAVE_NATIVE_COMP
   else if (SUBR_NATIVE_COMPILED_DYNP (fun))
     {
-      syms_left = XSUBR (fun)->lambda_list[0];
+      syms_left = XSUBR (fun)->lambda_list;
       lexenv = Qnil;
     }
+#endif
   else
     emacs_abort ();
 

src/lisp.h

@@ -2083,10 +2083,12 @@ struct Lisp_Subr
       Lisp_Object native_intspec;
     };
     EMACS_INT doc;
-    Lisp_Object native_comp_u[NATIVE_COMP_FLAG];
+#ifdef HAVE_NATIVE_COMP
-    char *native_c_name[NATIVE_COMP_FLAG];
+    Lisp_Object native_comp_u;
-    Lisp_Object lambda_list[NATIVE_COMP_FLAG];
+    char *native_c_name;
-    Lisp_Object type[NATIVE_COMP_FLAG];
+    Lisp_Object lambda_list;
+    Lisp_Object type;
+#endif
   } GCALIGNED_STRUCT;
 union Aligned_Lisp_Subr
   {
@@ -4773,19 +4775,19 @@ extern char *emacs_root_dir (void);
 INLINE bool
 SUBR_NATIVE_COMPILEDP (Lisp_Object a)
 {
-  return SUBRP (a) && !NILP (XSUBR (a)->native_comp_u[0]);
+  return SUBRP (a) && !NILP (XSUBR (a)->native_comp_u);
 }
 
 INLINE bool
 SUBR_NATIVE_COMPILED_DYNP (Lisp_Object a)
 {
-  return SUBR_NATIVE_COMPILEDP (a) && !NILP (XSUBR (a)->lambda_list[0]);
+  return SUBR_NATIVE_COMPILEDP (a) && !NILP (XSUBR (a)->lambda_list);
 }
 
 INLINE Lisp_Object
 SUBR_TYPE (Lisp_Object a)
 {
-  return XSUBR (a)->type[0];
+  return XSUBR (a)->type;
 }
 
 INLINE struct Lisp_Native_Comp_Unit *

src/lread.c

@@ -1271,7 +1271,10 @@ Return t if the file exists and loads successfully.  */)
               || suffix_p (file, MODULES_SECONDARY_SUFFIX)
 #endif
 #endif
-              || (NATIVE_COMP_FLAG && suffix_p (file, NATIVE_ELISP_SUFFIX)))
+#ifdef HAVE_NATIVE_COMP
+              || suffix_p (file, NATIVE_ELISP_SUFFIX)
+#endif
+	      )
 	    must_suffix = Qnil;
 	  /* Don't insist on adding a suffix
 	     if the argument includes a directory name.  */
@@ -1351,8 +1354,11 @@ Return t if the file exists and loads successfully.  */)
   bool is_module = false;
 #endif
 
-  bool is_native_elisp =
+#ifdef HAVE_NATIVE_COMP
-    NATIVE_COMP_FLAG && suffix_p (found, NATIVE_ELISP_SUFFIX) ? true : false;
+  bool is_native_elisp = suffix_p (found, NATIVE_ELISP_SUFFIX);
+#else
+  bool is_native_elisp = false;
+#endif
 
   /* Check if we're stuck in a recursive load cycle.
 

src/pdumper.c

@@ -2859,13 +2859,18 @@ dump_subr (struct dump_context *ctx, const struct Lisp_Subr *subr)
   struct Lisp_Subr out;
   dump_object_start (ctx, &out, sizeof (out));
   DUMP_FIELD_COPY (&out, subr, header.size);
-  if (NATIVE_COMP_FLAG && !NILP (subr->native_comp_u[0]))
+#ifdef HAVE_NATIVE_COMP
+  bool native_comp = !NILP (subr->native_comp_u);
+#else
+  bool native_comp = false;
+#endif
+  if (native_comp)
     out.function.a0 = NULL;
   else
     dump_field_emacs_ptr (ctx, &out, subr, &subr->function.a0);
   DUMP_FIELD_COPY (&out, subr, min_args);
   DUMP_FIELD_COPY (&out, subr, max_args);
-  if (NATIVE_COMP_FLAG && !NILP (subr->native_comp_u[0]))
+  if (native_comp)
     {
       dump_field_fixup_later (ctx, &out, subr, &subr->symbol_name);
       dump_remember_cold_op (ctx,
@@ -2879,19 +2884,16 @@ dump_subr (struct dump_context *ctx, const struct Lisp_Subr *subr)
       dump_field_emacs_ptr (ctx, &out, subr, &subr->intspec);
     }
   DUMP_FIELD_COPY (&out, subr, doc);
-  if (NATIVE_COMP_FLAG)
+#ifdef HAVE_NATIVE_COMP
-    {
+  dump_field_lv (ctx, &out, subr, &subr->native_comp_u, WEIGHT_NORMAL);
-      dump_field_lv (ctx, &out, subr, &subr->native_comp_u[0], WEIGHT_NORMAL);
+  if (!NILP (subr->native_comp_u))
-      if (!NILP (subr->native_comp_u[0]))
+    dump_field_fixup_later (ctx, &out, subr, &subr->native_c_name);
-	dump_field_fixup_later (ctx, &out, subr, &subr->native_c_name[0]);
 
-      dump_field_lv (ctx, &out, subr, &subr->lambda_list[0], WEIGHT_NORMAL);
+  dump_field_lv (ctx, &out, subr, &subr->lambda_list, WEIGHT_NORMAL);
-      dump_field_lv (ctx, &out, subr, &subr->type[0], WEIGHT_NORMAL);
+  dump_field_lv (ctx, &out, subr, &subr->type, WEIGHT_NORMAL);
-    }
+#endif
   dump_off subr_off = dump_object_finish (ctx, &out, sizeof (out));
-  if (NATIVE_COMP_FLAG
+  if (native_comp && ctx->flags.dump_object_contents)
-      && ctx->flags.dump_object_contents
-      && !NILP (subr->native_comp_u[0]))
     /* We'll do the final addr relocation during VERY_LATE_RELOCS time
        after the compilation units has been loaded. */
     dump_push (&ctx->dump_relocs[VERY_LATE_RELOCS],
@@ -3421,9 +3423,9 @@ dump_cold_native_subr (struct dump_context *ctx, Lisp_Object subr)
 
   dump_remember_fixup_ptr_raw
     (ctx,
-     subr_offset + dump_offsetof (struct Lisp_Subr, native_c_name[0]),
+     subr_offset + dump_offsetof (struct Lisp_Subr, native_c_name),
      ctx->offset);
-  const char *c_name = XSUBR (subr)->native_c_name[0];
+  const char *c_name = XSUBR (subr)->native_c_name;
   dump_write (ctx, c_name, 1 + strlen (c_name));
 }
 #endif
@@ -5360,20 +5362,16 @@ dump_do_dump_relocation (const uintptr_t dump_base,
       }
     case RELOC_NATIVE_SUBR:
       {
-	if (!NATIVE_COMP_FLAG)
-	  /* This cannot happen.  */
-	  emacs_abort ();
-
 	/* When resurrecting from a dump given non all the original
 	   native compiled subrs may be still around we can't rely on
 	   a 'top_level_run' mechanism, we revive them one-by-one
 	   here.  */
 	struct Lisp_Subr *subr = dump_ptr (dump_base, reloc_offset);
 	struct Lisp_Native_Comp_Unit *comp_u =
-	  XNATIVE_COMP_UNIT (subr->native_comp_u[0]);
+	  XNATIVE_COMP_UNIT (subr->native_comp_u);
 	if (!comp_u->handle)
 	  error ("NULL handle in compilation unit %s", SSDATA (comp_u->file));
-	const char *c_name = subr->native_c_name[0];
+	const char *c_name = subr->native_c_name;
 	eassert (c_name);
 	void *func = dynlib_sym (comp_u->handle, c_name);
 	if (!func)