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[Patch,AVR]: Fix PR56263

This patch implements a new warning option -Waddr-space-convert warns about
conversions to a non-containing address space.

Address spaces are implemented in such a way that each address space is
contained in each other space so that casting is possible, e.g. in code like

char read_c (bool in_flash, const char *str)
    if (in_flash)
      return * (const __flash char*) str;
      return *str;

However, there are no warning about implicit or explicit address space
conversions, which makes it hard to port progmem code to address space code.

If an address space qualifier is missing, e.g. when calling a function that is
not qualified correctly, this would result in wrong code (in contrast to
pgm_read that work no matter how the address is qualified).

There is still some work to do to get more precise warnings and this is just a
first take to implement PR56263, see the FIXME in the source.

The details can be worked out later, e.g. for 4.8.1.

Ok for trunk?

	PR target/56263
	* config/avr/avr.c (TARGET_CONVERT_TO_TYPE): Define to...
	(avr_convert_to_type): ...this new static function.
	* config/avr/avr.opt (-Waddr-space-convert): New C option.
	* doc/invoke.texi (AVR Options): Document it.
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
 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.
+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
 #define TARGET_FIXED_POINT_SUPPORTED_P hook_bool_void_true
+#define TARGET_CONVERT_TO_TYPE avr_convert_to_type
 #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

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