Added __objc_msg_forward...

Added __objc_msg_forward, a hook that allows external libraries to
provide a function that returns the real forwarding function. This can
alleviate problems __builtin_apply() and friends have on various
platforms. (Solution suggested by Helge Hess.)

Define gen_rtx_REG.

From-SVN: r38650

libobjc/sendmsg.c

@@ -33,6 +33,7 @@ Boston, MA 02111-1307, USA.  */
 /* this is how we hack STRUCT_VALUE to be 1 or 0 */
 #define gen_rtx(args...) 1
 #define gen_rtx_MEM(args...) 1
+#define gen_rtx_REG(args...) 1
 #define rtx int
 
 #if !defined(STRUCT_VALUE) || STRUCT_VALUE == 0
@@ -44,6 +45,11 @@ Boston, MA 02111-1307, USA.  */
 /* The uninstalled dispatch table */
 struct sarray* __objc_uninstalled_dtable = 0;   /* !T:MUTEX */
 
+/* Hook for method forwarding. If it is set, is invoked to return a
+   function that performs the real forwarding. Otherwise the libgcc
+   based functions (__builtin_apply and friends) are used. */
+IMP (*__objc_msg_forward)(SEL) = NULL;
+
 /* Send +initialize to class */
 static void __objc_send_initialize(Class);
 
@@ -76,18 +82,27 @@ __inline__
 IMP
 __objc_get_forward_imp (SEL sel)
 {
-  const char *t = sel->sel_types;
+  if (__objc_msg_forward)
+    {
+      IMP result;
+      if ((result = __objc_msg_forward (sel)))
+        return result;
+    }
+  else
+    {
+      const char *t = sel->sel_types;
 
-  if (t && (*t == '[' || *t == '(' || *t == '{')
+      if (t && (*t == '[' || *t == '(' || *t == '{')
 #ifdef OBJC_MAX_STRUCT_BY_VALUE
-    && objc_sizeof_type(t) > OBJC_MAX_STRUCT_BY_VALUE
+          && objc_sizeof_type(t) > OBJC_MAX_STRUCT_BY_VALUE
 #endif
-      )
-    return (IMP)__objc_block_forward;
-  else if (t && (*t == 'f' || *t == 'd'))
-    return (IMP)__objc_double_forward;
-  else
-    return (IMP)__objc_word_forward;
+          )
+        return (IMP)__objc_block_forward;
+      else if (t && (*t == 'f' || *t == 'd'))
+        return (IMP)__objc_double_forward;
+      else
+        return (IMP)__objc_word_forward;
+    }
 }
 
 /* Given a class and selector, return the selector's implementation.  */