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References: <bug-36015-87@http.gcc.gnu.org/bugzilla/>
Subject: [Bug target/36015] [4.3/4.4 Regression] -mregparm and fn decls without arguments
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From: "jakub at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
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------- Comment #4 from jakub at gcc dot gnu dot org  2008-04-23 13:29 -------
I've instead regtested:
--- gcc/config/i386/i386.c.jj   2008-04-01 13:34:27.000000000 +0200
+++ gcc/config/i386/i386.c      2008-04-23 13:38:14.000000000 +0200
@@ -3501,7 +3501,7 @@ init_cumulative_args (CUMULATIVE_ARGS *c
     {
       /* If there are variable arguments, then we won't pass anything
          in registers in 32-bit mode. */
-      if (cum->maybe_vaarg) 
+      if (stdarg_p (fntype))
        {
          cum->nregs = 0;
          cum->sse_nregs = 0;

patch (on i686 only, as this is !TARGET_64BIT hunk of code).
IMHO it best matches what 4.2 and earlier did.  Here is the 4.2 code:
  cum->maybe_vaarg = false;
...
  /* Determine if this function has variable arguments.  This is
     indicated by the last argument being 'void_type_mode' if there
     are no variable arguments.  If there are variable arguments, then
     we won't pass anything in registers in 32-bit mode. */

  if (cum->nregs || cum->mmx_nregs || cum->sse_nregs)
    {
      for (param = (fntype) ? TYPE_ARG_TYPES (fntype) : 0;
           param != 0; param = next_param)
        {
          next_param = TREE_CHAIN (param);
          if (next_param == 0 && TREE_VALUE (param) != void_type_node)
            {
              if (!TARGET_64BIT)
                {
                  cum->nregs = 0;
                  cum->sse_nregs = 0;
                  cum->mmx_nregs = 0;
                  cum->warn_sse = 0; 
                  cum->warn_mmx = 0; 
                  cum->fastcall = 0; 
                  cum->float_in_sse = 0;
                }
              cum->maybe_vaarg = true;
            }
        }
    }
  if ((!fntype && !libname)
      || (fntype && !TYPE_ARG_TYPES (fntype)))
    cum->maybe_vaarg = true;

The param/next_param testing IMHO is stdarg_p test, so cum->nregs etc. are
cleared only if !TARGET_64BIT && stdarg_p (fntype).  maybe_vaarg is set if
stdarg_p (fntype), or for fntype && !prototype_p (fntype), or for !fntype &&
!libname.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36015