Index: config/avr/avr-protos.h
===================================================================
--- config/avr/avr-protos.h	(Revision 171039)
+++ config/avr/avr-protos.h	(Arbeitskopie)
@@ -76,7 +76,7 @@ extern const char *lshrsi3_out (rtx insn
 extern bool avr_rotate_bytes (rtx operands[]);
 
 extern void expand_prologue (void);
-extern void expand_epilogue (void);
+extern void expand_epilogue (bool);
 extern int avr_epilogue_uses (int regno);
 
 extern void avr_output_bld (rtx operands[], int bit_nr);
Index: config/avr/avr.md
===================================================================
--- config/avr/avr.md	(Revision 171039)
+++ config/avr/avr.md	(Arbeitskopie)
@@ -2647,94 +2647,91 @@
 ;; call
 
 (define_expand "call"
-  [(call (match_operand:HI 0 "call_insn_operand" "")
-         (match_operand:HI 1 "general_operand" ""))]
+  [(parallel[(call (match_operand:HI 0 "call_insn_operand" "")
+                   (match_operand:HI 1 "general_operand" ""))
+             (use (const_int 0))])]
   ;; Operand 1 not used on the AVR.
+  ;; Operand 2 is 1 for tail-call, 0 otherwise.
+  ""
+  "")
+
+(define_expand "sibcall"
+  [(parallel[(call (match_operand:HI 0 "call_insn_operand" "")
+                   (match_operand:HI 1 "general_operand" ""))
+             (use (const_int 1))])]
+  ;; Operand 1 not used on the AVR.
+  ;; Operand 2 is 1 for tail-call, 0 otherwise.
   ""
   "")
 
 ;; call value
 
 (define_expand "call_value"
-  [(set (match_operand 0 "register_operand" "")
-        (call (match_operand:HI 1 "call_insn_operand" "")
-              (match_operand:HI 2 "general_operand" "")))]
+  [(parallel[(set (match_operand 0 "register_operand" "")
+                  (call (match_operand:HI 1 "call_insn_operand" "")
+                        (match_operand:HI 2 "general_operand" "")))
+             (use (const_int 0))])]
   ;; Operand 2 not used on the AVR.
+  ;; Operand 3 is 1 for tail-call, 0 otherwise.
   ""
   "")
 
-(define_insn "call_insn"
-  [(call (mem:HI (match_operand:HI 0 "nonmemory_operand" "!z,*r,s,n"))
-         (match_operand:HI 1 "general_operand" "X,X,X,X"))]
-;; We don't need in saving Z register because r30,r31 is a call used registers
+(define_expand "sibcall_value"
+  [(parallel[(set (match_operand 0 "register_operand" "")
+                  (call (match_operand:HI 1 "call_insn_operand" "")
+                        (match_operand:HI 2 "general_operand" "")))
+             (use (const_int 1))])]
+  ;; Operand 2 not used on the AVR.
+  ;; Operand 3 is 1 for tail-call, 0 otherwise.
+  ""
+  "")
+
+(define_insn "*call_insn"
+  [(parallel[(call (mem:HI (match_operand:HI 0 "nonmemory_operand" "z,s,z,s"))
+                   (match_operand:HI 1 "general_operand"           "X,X,X,X"))
+             (use (match_operand:HI 2 "const_int_operand"          "L,L,P,P"))])]
   ;; Operand 1 not used on the AVR.
-  "(register_operand (operands[0], HImode) || CONSTANT_P (operands[0]))"
-  "*{
-  if (which_alternative==0)
-     return \"%!icall\";
-  else if (which_alternative==1)
-    {
-      if (AVR_HAVE_MOVW)
-	return (AS2 (movw, r30, %0) CR_TAB
-               \"%!icall\");
-      else
-	return (AS2 (mov, r30, %A0) CR_TAB
-		AS2 (mov, r31, %B0) CR_TAB
-		\"%!icall\");
-    }
-  else if (which_alternative==2)
-    return AS1(%~call,%x0);
-  return (AS2 (ldi,r30,lo8(%0)) CR_TAB
-          AS2 (ldi,r31,hi8(%0)) CR_TAB
-          \"%!icall\");
-}"
-  [(set_attr "cc" "clobber,clobber,clobber,clobber")
+  ;; Operand 2 is 1 for tail-call, 0 otherwise.
+  ""
+  "@
+    %!icall
+    %~call %x0
+    %!ijmp
+    %~jmp %x0"
+  [(set_attr "cc" "clobber")
    (set_attr_alternative "length"
-			 [(const_int 1)
-			  (if_then_else (eq_attr "mcu_have_movw" "yes")
-					(const_int 2)
-					(const_int 3))
-			  (if_then_else (eq_attr "mcu_mega" "yes")
-					(const_int 2)
-					(const_int 1))
-			  (const_int 3)])])
-
-(define_insn "call_value_insn"
-  [(set (match_operand 0 "register_operand" "=r,r,r,r")
-        (call (mem:HI (match_operand:HI 1 "nonmemory_operand" "!z,*r,s,n"))
-;; We don't need in saving Z register because r30,r31 is a call used registers
-              (match_operand:HI 2 "general_operand" "X,X,X,X")))]
+                         [(const_int 1)
+                          (if_then_else (eq_attr "mcu_mega" "yes")
+                                        (const_int 2)
+                                        (const_int 1))
+                          (const_int 1)
+                          (if_then_else (eq_attr "mcu_mega" "yes")
+                                        (const_int 2)
+                                        (const_int 1))])])
+
+(define_insn "*call_value_insn"
+  [(parallel[(set (match_operand 0 "register_operand"                   "=r,r,r,r")
+                  (call (mem:HI (match_operand:HI 1 "nonmemory_operand"  "z,s,z,s"))
+                        (match_operand:HI 2 "general_operand"            "X,X,X,X")))
+             (use (match_operand:HI 3 "const_int_operand"                "L,L,P,P"))])]
   ;; Operand 2 not used on the AVR.
-  "(register_operand (operands[0], VOIDmode) || CONSTANT_P (operands[0]))"
-  "*{
-  if (which_alternative==0)
-     return \"%!icall\";
-  else if (which_alternative==1)
-    {
-      if (AVR_HAVE_MOVW)
-	return (AS2 (movw, r30, %1) CR_TAB
-		\"%!icall\");
-      else
-	return (AS2 (mov, r30, %A1) CR_TAB
-		AS2 (mov, r31, %B1) CR_TAB
-		\"%!icall\");
-    }
-  else if (which_alternative==2)
-    return AS1(%~call,%x1);
-  return (AS2 (ldi, r30, lo8(%1)) CR_TAB
-          AS2 (ldi, r31, hi8(%1)) CR_TAB
-          \"%!icall\");
-}"
-  [(set_attr "cc" "clobber,clobber,clobber,clobber")
+  ;; Operand 3 is 1 for tail-call, 0 otherwise.
+  ""
+  "@
+    %!icall
+    %~call %x1
+    %!ijmp
+    %~jmp %x1"
+  [(set_attr "cc" "clobber")
    (set_attr_alternative "length"
-			 [(const_int 1)
-			  (if_then_else (eq_attr "mcu_have_movw" "yes")
-					(const_int 2)
-					(const_int 3))
-			  (if_then_else (eq_attr "mcu_mega" "yes")
-					(const_int 2)
-					(const_int 1))
-			  (const_int 3)])])
+                         [(const_int 1)
+                          (if_then_else (eq_attr "mcu_mega" "yes")
+                                        (const_int 2)
+                                        (const_int 1))
+                          (const_int 1)
+                          (if_then_else (eq_attr "mcu_mega" "yes")
+                                        (const_int 2)
+                                        (const_int 1))])])
 
 (define_insn "nop"
   [(const_int 0)]
@@ -3246,8 +3243,15 @@
 (define_expand "epilogue"
   [(const_int 0)]
   ""
-  "
   {
-    expand_epilogue (); 
+    expand_epilogue (false /* sibcall_p */);
     DONE;
-  }")
+  })
+
+(define_expand "sibcall_epilogue"
+  [(const_int 0)]
+  ""
+  {
+    expand_epilogue (true /* sibcall_p */);
+    DONE;
+  })
Index: config/avr/avr.c
===================================================================
--- config/avr/avr.c	(Revision 171039)
+++ config/avr/avr.c	(Arbeitskopie)
@@ -100,6 +100,7 @@ static rtx avr_function_arg (CUMULATIVE_
 static void avr_function_arg_advance (CUMULATIVE_ARGS *, enum machine_mode,
 				      const_tree, bool);
 static void avr_help (void);
+static bool avr_function_ok_for_sibcall (tree, tree);
 
 /* Allocate registers from r25 to r8 for parameters for function calls.  */
 #define FIRST_CUM_REG 26
@@ -231,6 +232,9 @@ static const struct default_options avr_
 #undef TARGET_HELP
 #define TARGET_HELP avr_help
 
+#undef TARGET_FUNCTION_OK_FOR_SIBCALL
+#define TARGET_FUNCTION_OK_FOR_SIBCALL avr_function_ok_for_sibcall
+
 struct gcc_target targetm = TARGET_INITIALIZER;
 
 static void
@@ -330,17 +334,34 @@ avr_regno_reg_class (int r)
   return ALL_REGS;
 }
 
+/* A helper for the subsequent function attribute used to dig for
+   attribute 'name' in a FUNCTION_DECL or FUNCTION_TYPE */
+
+static inline int
+avr_lookup_function_attribute1 (const_tree func, const char *name)
+{
+  if (FUNCTION_DECL == TREE_CODE (func))
+    {
+      if (NULL_TREE != lookup_attribute (name, DECL_ATTRIBUTES (func)))
+        {
+          return true;
+        }
+      
+      func = TREE_TYPE (func);
+    }
+
+  gcc_assert (TREE_CODE (func) == FUNCTION_TYPE
+              || TREE_CODE (func) == METHOD_TYPE);
+  
+  return NULL_TREE != lookup_attribute (name, TYPE_ATTRIBUTES (func));
+}
+
 /* Return nonzero if FUNC is a naked function.  */
 
 static int
 avr_naked_function_p (tree func)
 {
-  tree a;
-
-  gcc_assert (TREE_CODE (func) == FUNCTION_DECL);
-  
-  a = lookup_attribute ("naked", TYPE_ATTRIBUTES (TREE_TYPE (func)));
-  return a != NULL_TREE;
+  return avr_lookup_function_attribute1 (func, "naked");
 }
 
 /* Return nonzero if FUNC is an interrupt function as specified
@@ -349,13 +370,7 @@ avr_naked_function_p (tree func)
 static int
 interrupt_function_p (tree func)
 {
-  tree a;
-
-  if (TREE_CODE (func) != FUNCTION_DECL)
-    return 0;
-
-  a = lookup_attribute ("interrupt", DECL_ATTRIBUTES (func));
-  return a != NULL_TREE;
+  return avr_lookup_function_attribute1 (func, "interrupt");
 }
 
 /* Return nonzero if FUNC is a signal function as specified
@@ -364,13 +379,7 @@ interrupt_function_p (tree func)
 static int
 signal_function_p (tree func)
 {
-  tree a;
-
-  if (TREE_CODE (func) != FUNCTION_DECL)
-    return 0;
-
-  a = lookup_attribute ("signal", DECL_ATTRIBUTES (func));
-  return a != NULL_TREE;
+  return avr_lookup_function_attribute1 (func, "signal");
 }
 
 /* Return nonzero if FUNC is a OS_task function.  */
@@ -378,12 +387,7 @@ signal_function_p (tree func)
 static int
 avr_OS_task_function_p (tree func)
 {
-  tree a;
-
-  gcc_assert (TREE_CODE (func) == FUNCTION_DECL);
-  
-  a = lookup_attribute ("OS_task", TYPE_ATTRIBUTES (TREE_TYPE (func)));
-  return a != NULL_TREE;
+  return avr_lookup_function_attribute1 (func, "OS_task");
 }
 
 /* Return nonzero if FUNC is a OS_main function.  */
@@ -391,12 +395,7 @@ avr_OS_task_function_p (tree func)
 static int
 avr_OS_main_function_p (tree func)
 {
-  tree a;
-
-  gcc_assert (TREE_CODE (func) == FUNCTION_DECL);
-  
-  a = lookup_attribute ("OS_main", TYPE_ATTRIBUTES (TREE_TYPE (func)));
-  return a != NULL_TREE;
+  return avr_lookup_function_attribute1 (func, "OS_main");
 }
 
 /* Return the number of hard registers to push/pop in the prologue/epilogue
@@ -864,7 +863,7 @@ avr_epilogue_uses (int regno ATTRIBUTE_U
 /*  Output RTL epilogue.  */
 
 void
-expand_epilogue (void)
+expand_epilogue (bool sibcall_p)
 {
   int reg;
   int live_seq;
@@ -875,6 +874,8 @@ expand_epilogue (void)
   /* epilogue: naked  */
   if (cfun->machine->is_naked)
     {
+      gcc_assert (!sibcall_p);
+      
       emit_jump_insn (gen_return ());
       return;
     }
@@ -1016,7 +1017,8 @@ expand_epilogue (void)
           emit_insn (gen_popqi (zero_reg_rtx));
         }
 
-      emit_jump_insn (gen_return ());
+      if (!sibcall_p)
+        emit_jump_insn (gen_return ());
     }
 }
 
@@ -1629,6 +1631,10 @@ init_cumulative_args (CUMULATIVE_ARGS *c
   cum->regno = FIRST_CUM_REG;
   if (!libname && stdarg_p (fntype))
     cum->nregs = 0;
+
+  /* Assume the calle may be tail called */
+  
+  cfun->machine->sibcall_fails = 0;
 }
 
 /* Returns the number of registers to allocate for a function argument.  */
@@ -1676,6 +1682,23 @@ avr_function_arg_advance (CUMULATIVE_ARG
   cum->nregs -= bytes;
   cum->regno -= bytes;
 
+  /* A parameter is being passed in a call-saved register. As the original
+     contents of these regs has to be restored before leaving the function,
+     a function must not pass arguments in call-saved regs in order to get
+     tail-called. */
+  
+  if (cum->regno >= 0
+      && !call_used_regs[cum->regno])
+    {
+      /* FIXME: We ship info on failing tail-call in struct machine_function.
+         This uses internals of calls.c:expand_call() and the way args_so_far
+         is used. targetm.function_ok_for_sibcall() needs to be extended to
+         pass &args_so_far, too. At present, CUMULATIVE_ARGS is target
+         dependent so that such an extension is not wanted. */
+      
+      cfun->machine->sibcall_fails = 1;
+    }
+
   if (cum->nregs <= 0)
     {
       cum->nregs = 0;
@@ -1683,6 +1706,62 @@ avr_function_arg_advance (CUMULATIVE_ARG
     }
 }
 
+/* Implement `TARGET_FUNCTION_OK_FOR_SIBCALL' */
+/* Decide whether we can make a sibling call to a function.  DECL is the
+   declaration of the function being targeted by the call and EXP is the
+   CALL_EXPR representing the call. */
+
+static bool
+avr_function_ok_for_sibcall (tree decl_callee, tree exp_callee)
+{
+  tree fntype_callee;
+
+  /* Tail-calling must fail if callee-saved regs are used to pass
+     function args.  We must not tail-call when `epilogue_restores'
+     is used.  Unfortunately, we cannot tell at this point if that
+     actually will happen or not, and we cannot step back from
+     tail-calling. Thus, we inhibit tail-calling with -mcall-prologues. */
+  
+  if (cfun->machine->sibcall_fails
+      || TARGET_CALL_PROLOGUES)
+    {
+      return false;
+    }
+  
+  fntype_callee = TREE_TYPE (CALL_EXPR_FN (exp_callee));
+
+  if (decl_callee)
+    {
+      decl_callee = TREE_TYPE (decl_callee);
+    }
+  else
+    {
+      decl_callee = fntype_callee;
+      
+      while (FUNCTION_TYPE != TREE_CODE (decl_callee)
+             && METHOD_TYPE != TREE_CODE (decl_callee))
+        {
+          decl_callee = TREE_TYPE (decl_callee);
+        }
+    }
+
+  /* Ensure that caller and callee have compatible epilogues */
+  
+  if (interrupt_function_p (current_function_decl)
+      || signal_function_p (current_function_decl)
+      || avr_naked_function_p (decl_callee)
+      || avr_naked_function_p (current_function_decl)
+      || (avr_OS_task_function_p (decl_callee)
+          != avr_OS_task_function_p (current_function_decl))
+      || (avr_OS_main_function_p (decl_callee)
+          != avr_OS_main_function_p (current_function_decl)))
+    {
+      return false;
+    }
+ 
+  return true;
+}
+
 /***********************************************************************
   Functions for outputting various mov's for a various modes
 ************************************************************************/
Index: config/avr/avr.opt
===================================================================
--- config/avr/avr.opt	(Revision 171039)
+++ config/avr/avr.opt	(Arbeitskopie)
@@ -29,6 +29,9 @@ Target RejectNegative Joined Var(avr_mcu
 mdeb
 Target Report Undocumented Mask(ALL_DEBUG)
 
+mtest=
+Target RejectNegative Report Joined Undocumented UInteger Var(avr_test) Init(0)
+
 mint8
 Target Report Mask(INT8)
 Use an 8-bit 'int' type
Index: config/avr/avr.h
===================================================================
--- config/avr/avr.h	(Revision 171039)
+++ config/avr/avr.h	(Arbeitskopie)
@@ -828,4 +828,7 @@ struct GTY(()) machine_function
   
   /* Current function stack size.  */
   int stack_usage;
+
+  /* 'true' if a callee might be tail called */
+  int sibcall_fails;
 };
