[Patch,AVR]: ad PR49868: assemble 3-byte symbols

[Georg-Johann Lay <avr at gjlay dot de>]

Currently avr_assemble_integer emits an assembler warning to
make gas complain about missing feature

http://sourceware.org/PR13503

if a 3-byte address must be assembled.

As PR13503 is implemented now, avr-gcc can use this feature.

It's only needed for the new __memx address space.

Ok to install?

The feature is new in gcc and binutils and only rarely
used, IMHO. The current solution will throw a comprehensible
warning but generate bad code, with the patch old binutils
will throw a not really helpful diagnose but work with
new binutils...

Thus okay to backport? Or leave 4.7 as is?

Johann

	PR target/46898
	* config/avr/avr.c (avr_const_address_lo16): Remove.
	(avr_assemble_integer):  Print ".byte lo8(x)",
	".byte hi8(x)", ".byte hh8(x)" instead of emit an assembler
	.warning if 3-byte address is assembled.

	* doc/extend.texi (AVR Named Address Spaces): Document that
	binutils 2.23 is needed to assemble 3-byte addresses.

Index: config/avr/avr.c
===================================================================
--- config/avr/avr.c	(revision 187411)
+++ config/avr/avr.c	(working copy)
@@ -6639,48 +6639,6 @@ _reg_unused_after (rtx insn, rtx reg)
 }
 
 
-/* Return RTX that represents the lower 16 bits of a constant address.
-   Unfortunately, simplify_gen_subreg does not handle this case.  */
-
-static rtx
-avr_const_address_lo16 (rtx x)
-{
-  rtx lo16;
-  
-  switch (GET_CODE (x))
-    {
-    default:
-      break;
-      
-    case CONST:
-      if (PLUS == GET_CODE (XEXP (x, 0))
-          && SYMBOL_REF == GET_CODE (XEXP (XEXP (x, 0), 0))
-          && CONST_INT_P (XEXP (XEXP (x, 0), 1)))
-        {
-          HOST_WIDE_INT offset = INTVAL (XEXP (XEXP (x, 0), 1));
-          const char *name = XSTR (XEXP (XEXP (x, 0), 0), 0);
-          
-          lo16 = gen_rtx_SYMBOL_REF (Pmode, ggc_strdup (name));
-          lo16 = gen_rtx_CONST (Pmode, plus_constant (Pmode, lo16, offset));
-          
-          return lo16;
-        }
-      
-      break;
-      
-    case SYMBOL_REF:
-      {
-        const char *name = XSTR (x, 0);
-        
-        return gen_rtx_SYMBOL_REF (Pmode, ggc_strdup (name));
-      }
-    }
-  
-  avr_edump ("\n%?: %r\n", x);
-  gcc_unreachable();
-}
-
-
 /* Target hook for assembling integer objects.  The AVR version needs
    special handling for references to certain labels.  */
 
@@ -6688,7 +6646,7 @@ static bool
 avr_assemble_integer (rtx x, unsigned int size, int aligned_p)
 {
   if (size == POINTER_SIZE / BITS_PER_UNIT && aligned_p
-      && text_segment_operand (x, VOIDmode) )
+      && text_segment_operand (x, VOIDmode))
     {
       fputs ("\t.word\tgs(", asm_out_file);
       output_addr_const (asm_out_file, x);
@@ -6698,15 +6656,17 @@ avr_assemble_integer (rtx x, unsigned in
     }
   else if (GET_MODE (x) == PSImode)
     {
-      default_assemble_integer (avr_const_address_lo16 (x),
-                                GET_MODE_SIZE (HImode), aligned_p);
+      /* This needs binutils 2.23+, see PR binutils/13503  */
+
+      fputs ("\t.byte\tlo8(", asm_out_file);
+      output_addr_const (asm_out_file, x);
+      fputs (")\n", asm_out_file);
       
-      fputs ("\t.warning\t\"assembling 24-bit address needs binutils"
-             " extension for hh8(", asm_out_file);
+      fputs ("\t.byte\thi8(", asm_out_file);
       output_addr_const (asm_out_file, x);
-      fputs (")\"\n", asm_out_file);
+      fputs (")\n", asm_out_file);
       
-      fputs ("\t.byte\t0\t" ASM_COMMENT_START " hh8(", asm_out_file);
+      fputs ("\t.byte\thh8(", asm_out_file);
       output_addr_const (asm_out_file, x);
       fputs (")\n", asm_out_file);
       
Index: doc/extend.texi
===================================================================
--- doc/extend.texi	(revision 187411)
+++ doc/extend.texi	(working copy)
@@ -1273,6 +1273,7 @@ If the high bit of the address is set, d
 RAM using the lower two bytes as RAM address.
 If the high bit of the address is clear, data is read from flash
 with @code{RAMPZ} set according to the high byte of the address.
+@xref{AVR Built-in Functions,,@code{__builtin_avr_flash_segment}}.
 
 Objects in this address space will be located in @code{.progmem.data}.
 @end table
@@ -1302,6 +1303,7 @@ int main (void)
 @}
 @end example
 
+@noindent
 For each named address space supported by avr-gcc there is an equally
 named but uppercase built-in macro defined. 
 The purpose is to facilitate testing if respective address space
@@ -1327,7 +1329,8 @@ int read_var (void)
 #endif /* __FLASH */
 @end example
 
-Notice that attribute @ref{AVR Variable Attributes,@code{progmem}}
+@noindent
+Notice that attribute @ref{AVR Variable Attributes,,@code{progmem}}
 locates data in flash but
 accesses to these data will read from generic address space, i.e.@:
 from RAM,
@@ -1335,6 +1338,7 @@ so that you need special accessors like
 from @w{@uref{http://nongnu.org/avr-libc/user-manual,AVR-LibC}}
 together with attribute @code{progmem}.
 
+@noindent
 @b{Limitations and caveats}
 
 @itemize
@@ -1361,17 +1365,14 @@ must not optimize away known values or i
 as immediates into operands of instructions.
 
 @item
-Code like the following is not yet supported because of missing
-support in avr-binutils,
-see @w{@uref{http://sourceware.org/PR13503,PR13503}}.
+The following code initializes a variable @code{pfoo}
+located in static storage with a 24-bit address:
 @example
 extern const __memx char foo;
 const __memx void *pfoo = &foo;
 @end example
-The code will throw an assembler warning and the high byte of
-@code{pfoo} will be initialized with@tie{}@code{0}, i.e.@: the
-initialization will be as if @code{foo} was located in the first
-64@tie{}KiB chunk of flash.
+Such code requires at least binutils 2.23, see
+@w{@uref{http://sourceware.org/PR13503,PR13503}}.
 
 @end itemize