Add DW_AT_const_value as unsigned or int depending on type and value used.

As the comment in the code already indicated DWARF2 does provide
DW_FORM_sdata/DW_FORM_udata to represent signed/unsigned data.
Enumeration constants wider than HOST_WIDE_INT are already handled
separately. Those constant values that do fit a HOST_WIDE_INT can
be encoded as signed or unsigned depending on type and value for
more efficient encoding.

	* dwarf2out.c (gen_enumeration_type_die): Add DW_AT_const_value
	as unsigned or int depending on type and value used.

From-SVN: r209424

gcc/ChangeLog

+2014-03-21  Mark Wielaard  <mjw@redhat.com>
+
+	* dwarf2out.c (gen_enumeration_type_die): Add DW_AT_const_value
+	as unsigned or int depending on type and value used.
+
 2014-04-15  Richard Biener  <rguenther@suse.de>
 
 	PR rtl-optimization/56965

gcc/dwarf2out.c

@@ -17361,22 +17361,23 @@ gen_enumeration_type_die (tree type, dw_die_ref context_die)
 
 	  if (simple_type_size_in_bits (TREE_TYPE (value))
 	      <= HOST_BITS_PER_WIDE_INT || tree_fits_shwi_p (value))
-	    /* DWARF2 does not provide a way of indicating whether or
-	       not enumeration constants are signed or unsigned.  GDB
-	       always assumes the values are signed, so we output all
-	       values as if they were signed.  That means that
-	       enumeration constants with very large unsigned values
-	       will appear to have negative values in the debugger.
-
-	       TODO: the above comment is wrong, DWARF2 does provide
-	       DW_FORM_sdata/DW_FORM_udata to represent signed/unsigned data.
-	       This should be re-worked to use correct signed/unsigned
-	       int/double tags for all cases, instead of always treating as
-	       signed.  */
-	    add_AT_int (enum_die, DW_AT_const_value, TREE_INT_CST_LOW (value));
+	    {
+	      /* For constant forms created by add_AT_unsigned DWARF
+		 consumers (GDB, elfutils, etc.) always zero extend
+		 the value.  Only when the actual value is negative
+		 do we need to use add_AT_int to generate a constant
+		 form that can represent negative values.  */
+	      HOST_WIDE_INT val = TREE_INT_CST_LOW (value);
+	      if (TYPE_UNSIGNED (TREE_TYPE (value)) || val >= 0)
+		add_AT_unsigned (enum_die, DW_AT_const_value,
+				 (unsigned HOST_WIDE_INT) val);
+	      else
+		add_AT_int (enum_die, DW_AT_const_value, val);
+	    }
 	  else
 	    /* Enumeration constants may be wider than HOST_WIDE_INT.  Handle
-	       that here.  */
+	       that here.  TODO: This should be re-worked to use correct
+	       signed/unsigned double tags for all cases.  */
 	    add_AT_double (enum_die, DW_AT_const_value,
 			   TREE_INT_CST_HIGH (value), TREE_INT_CST_LOW (value));
 	}