[m68k] Restore -mrtd

[Bernardo Innocenti <bernie at develer dot com>]

This patch restores the -mrtd option previously removed during target
cleanup, as discussed with Gunther.

And the good news is that it even works fine, as shown in this testcase:

int foo(int a, int b, char *c)
{
    printf(c, a ,b);
}

int bar(void)
{
    extern int a;
    extern char b;
    extern char *c;
    return foo(a, b, c);
}

foo:
    link.w %a6,#0
    move.l 12(%a6),-(%sp)
    move.l 8(%a6),-(%sp)
    move.l 16(%a6),-(%sp)
    jbsr printf
    lea (12,%sp),%sp
    unlk %a6
    rtd #12
bar:
    link.w %a6,#0
    move.l c,-(%sp)
    move.b b,%d0
    extb.l %d0
    move.l %d0,-(%sp)
    move.l a,-(%sp)
    jbsr foo
    unlk %a6
    rts

2003-09-21  Bernardo Innocenti  <bernie@develer.com>

	* config/m68k/m68k.h (MASK_RTD, TARGET_RTD, MASK_REGPARM,
	TARGET_REGPARM, RETURN_POPS_ARGS): Resurrect -mrtd option.

diff -u -3 -p -u -p -r1.96 m68k.h
--- gcc/config/m68k/m68k.h	19 Sep 2003 16:39:44 -0000	1.96
+++ gcc/config/m68k/m68k.h	21 Sep 2003 12:15:50 -0000
@@ -201,6 +201,11 @@ extern int target_flags;
#define MASK_NO_STRICT_ALIGNMENT (1<<15)
#define TARGET_STRICT_ALIGNMENT  (~target_flags & MASK_NO_STRICT_ALIGNMENT)

+/* Compile using rtd insn calling sequence.
+   This will not work unless you use prototypes at least
+   for all functions that can take varying numbers of args.  */
+#define MASK_RTD	(1<<16)
+#define TARGET_RTD	(target_flags & MASK_RTD)

/* Compile for a CPU32.  A 68020 without bitfields is a good
   heuristic for a CPU32.  */
@@ -306,6 +311,10 @@ extern int target_flags;
      N_("Do not use unaligned memory references") },			\
    { "no-strict-align", MASK_NO_STRICT_ALIGNMENT,			\
      N_("Use unaligned memory references") },				\
+    { "rtd", MASK_RTD,							\
+      N_("Use different calling convention using 'rtd'") },		\
+    { "nortd", - MASK_RTD,						\
+      N_("Use normal calling convention") },				\
    SUBTARGET_SWITCHES							\
    { "", TARGET_DEFAULT, "" }}
/* TARGET_DEFAULT is defined in m68k-none.h, netbsd.h, etc.  */
@@ -790,9 +799,21 @@ enum reg_class {
   or for a library call it is an identifier node for the subroutine name.
   SIZE is the number of bytes of arguments passed on the stack.

-   On the m68k, the caller must always pop the args. */
-
-#define RETURN_POPS_ARGS(FUNDECL,FUNTYPE,SIZE) 0
+   On the 68000, the RTS insn cannot pop anything.
+   On the 68010, the RTD insn may be used to pop them if the number
+     of args is fixed, but if the number is variable then the caller
+     must pop them all.  RTD can't be used for library calls now
+     because the library is compiled with the Unix compiler.
+   Use of RTD is a selectable option, since it is incompatible with
+   standard Unix calling sequences.  If the option is not selected,
+   the caller must always pop the args.  */
+
+#define RETURN_POPS_ARGS(FUNDECL,FUNTYPE,SIZE)   \
+  ((TARGET_RTD && (!(FUNDECL) || TREE_CODE (FUNDECL) != IDENTIFIER_NODE)	\
+    && (TYPE_ARG_TYPES (FUNTYPE) == 0				\
+	|| (TREE_VALUE (tree_last (TYPE_ARG_TYPES (FUNTYPE)))	\
+	    == void_type_node)))				\
+   ? (SIZE) : 0)

/* Define how to find the value returned by a function.
   VALTYPE is the data type of the value (as a tree).

--
 // Bernardo Innocenti - Develer S.r.l., R&D dept.
\X/  http://www.develer.com/

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