Index: config/avr/avr.opt
===================================================================
--- config/avr/avr.opt	(revision 196495)
+++ config/avr/avr.opt	(working copy)
@@ -74,3 +74,7 @@ When accessing RAM, use X as imposed by
 msp8
 Target Report RejectNegative Var(avr_sp8) Init(0)
 The device has no SPH special function register. This option will be overridden by the compiler driver with the correct setting if presence/absence of SPH can be deduced from -mmcu=MCU.
+
+Waddr-space-convert
+Warning C Report Var(avr_warn_addr_space_convert) Init(0)
+Warn if the address space of an address is change.
Index: config/avr/avr.c
===================================================================
--- config/avr/avr.c	(revision 196495)
+++ config/avr/avr.c	(working copy)
@@ -10765,6 +10765,42 @@ avr_addr_space_subset_p (addr_space_t su
 }
 
 
+/* Implement `TARGET_CONVERT_TO_TYPE'.  */
+
+static tree
+avr_convert_to_type (tree type, tree expr)
+{
+  if (avr_warn_addr_space_convert
+      && expr != error_mark_node
+      && POINTER_TYPE_P (type)
+      && POINTER_TYPE_P (TREE_TYPE (expr)))
+    {
+      addr_space_t as_old = TYPE_ADDR_SPACE (TREE_TYPE (TREE_TYPE (expr)));
+      addr_space_t as_new = TYPE_ADDR_SPACE (TREE_TYPE (type));
+        
+      if (avr_log.progmem)
+        avr_edump ("%?: type = %t\nexpr = %t\n\n", type, expr);
+
+      if (as_new != ADDR_SPACE_MEMX
+          && as_new != as_old)
+        {
+          location_t loc = EXPR_LOCATION (expr);
+          const char *name_old = avr_addrspace[as_old].name;
+          const char *name_new = avr_addrspace[as_new].name;
+
+          warning (OPT_Waddr_space_convert,
+                   "conversion from address space %qs to address space %qs",
+                   ADDR_SPACE_GENERIC_P (as_old) ? "generic" : name_old,
+                   ADDR_SPACE_GENERIC_P (as_new) ? "generic" : name_new);
+
+          return fold_build1_loc (loc, ADDR_SPACE_CONVERT_EXPR, type, expr);
+        }
+    }
+
+  return NULL_TREE;
+}
+
+
 /* Worker function for movmemhi expander.
    XOP[0]  Destination as MEM:BLK
    XOP[1]  Source      "     "
@@ -12149,6 +12185,9 @@ avr_fold_builtin (tree fndecl, int n_arg
 #undef  TARGET_FIXED_POINT_SUPPORTED_P
 #define TARGET_FIXED_POINT_SUPPORTED_P hook_bool_void_true
 
+#undef  TARGET_CONVERT_TO_TYPE
+#define TARGET_CONVERT_TO_TYPE avr_convert_to_type
+
 #undef  TARGET_ADDR_SPACE_SUBSET_P
 #define TARGET_ADDR_SPACE_SUBSET_P avr_addr_space_subset_p
 
Index: doc/invoke.texi
===================================================================
--- doc/invoke.texi	(revision 196495)
+++ doc/invoke.texi	(working copy)
@@ -514,7 +514,7 @@ Objective-C and Objective-C++ Dialects}.
 @emph{AVR Options}
 @gccoptlist{-mmcu=@var{mcu} -maccumulate-args -mbranch-cost=@var{cost} @gol
 -mcall-prologues -mint8 -mno-interrupts -mrelax @gol
--mstrict-X -mtiny-stack}
+-mstrict-X -mtiny-stack -Waddr-space-convert}
 
 @emph{Blackfin Options}
 @gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol
@@ -11653,6 +11653,11 @@ when @code{EICALL} or @code{EIJMP} instr
 Indirect jumps and calls on these devices are handled as follows by
 the compiler and are subject to some limitations:
 
+@item -Waddr-space-convert
+@opindex Waddr-space-convert
+Warn about conversions between address spaces in the case where the
+resulting address space is not contained in the incoming address space.
+
 @itemize @bullet
 
 @item