Index: config/avr/avr.c
===================================================================
--- config/avr/avr.c	(Revision 174701)
+++ config/avr/avr.c	(Arbeitskopie)
@@ -6276,26 +6276,35 @@ jump_over_one_insn_p (rtx insn, rtx dest
 int
 avr_hard_regno_mode_ok (int regno, enum machine_mode mode)
 {
-  /* Disallow QImode in stack pointer regs.  */
-  if ((regno == REG_SP || regno == (REG_SP + 1)) && mode == QImode)
+  /* Don't allocate data to non-GENERAL_REGS registers.  */
+  
+  if (regno >= 32)
     return 0;
 
-  /* The only thing that can go into registers r28:r29 is a Pmode.  */
-  if (regno == REG_Y && mode == Pmode)
+  /* Any GENERAL_REGS register can hold 8-bit values.  */
+  /* FIXME:
+     8-bit values must not be disallowed for R28 or R29.  Disallowing
+     QI et al. in these registers might lead to code like
+         (set (subreg:QI (reg:HI 28)) ...)
+     which will result in wrong code because reload does not handle
+     SUBREGs of hard regsisters like this.  This could be fixed in reload.
+     However, it appears that fixing reload is not wanted by reload people.  */
+  
+  if (GET_MODE_SIZE (mode) == 1)
     return 1;
+  
+  /* Disallow big registers that overlap the frame pointer.
+     This will hopefully reduce the number of spill failures.  */
+  
+  if (GET_MODE_SIZE (mode) > 2
+      && regno <= REG_Y
+      && regno + GET_MODE_SIZE (mode) >= REG_Y + 1)
+    {
+      return 0;
+    }
 
-  /* Otherwise disallow all regno/mode combinations that span r28:r29.  */
-  if (regno <= (REG_Y + 1) && (regno + GET_MODE_SIZE (mode)) >= (REG_Y + 1))
-    return 0;
-
-  if (mode == QImode)
-    return 1;
-
-  /* Modes larger than QImode occupy consecutive registers.  */
-  if (regno + GET_MODE_SIZE (mode) > FIRST_PSEUDO_REGISTER)
-    return 0;
-
-  /* All modes larger than QImode should start in an even register.  */
+  /* All modes larger than 8 bits should start in an even register.  */
+  
   return !(regno & 1);
 }
 
@@ -6422,13 +6431,23 @@ avr_hard_regno_scratch_ok (unsigned int
       && !df_regs_ever_live_p (regno))
     return false;
 
+  /* Don't allow hard registers that might be part of the frame pointer.
+     Some places in the compiler just test for [HARD_]FRAME_POINTER_REGNUM
+     and don't care for a frame pointer that spans more than one register.  */
+
+  if ((!reload_completed || frame_pointer_needed)
+      && (regno == REG_Y || regno == REG_Y + 1))
+    {
+      return false;
+    }
+
   return true;
 }
 
 /* Return nonzero if register OLD_REG can be renamed to register NEW_REG.  */
 
 int
-avr_hard_regno_rename_ok (unsigned int old_reg ATTRIBUTE_UNUSED,
+avr_hard_regno_rename_ok (unsigned int old_reg,
 			  unsigned int new_reg)
 {
   /* Interrupt functions can only use registers that have already been
@@ -6439,6 +6458,17 @@ avr_hard_regno_rename_ok (unsigned int o
       && !df_regs_ever_live_p (new_reg))
     return 0;
 
+  /* Don't allow hard registers that might be part of the frame pointer.
+     Some places in the compiler just test for [HARD_]FRAME_POINTER_REGNUM
+     and don't care for a frame pointer that spans more than one register.  */
+
+  if ((!reload_completed || frame_pointer_needed)
+      && (old_reg == REG_Y || old_reg == REG_Y + 1
+          || new_reg == REG_Y || new_reg == REG_Y + 1))
+    {
+      return 0;
+    }
+  
   return 1;
 }