DWARF: add a language hook for scalar biased types

Front-ends like GNAT for Ada sometimes use biased encodings for integral
types.  This change creates a new language hook so that the bias
information can make it into the debugging information back-end and
introduces an experimental DWARF attribute to hold it.

gcc/ada/ChangeLog:

	* gcc-interface/misc.c (gnat_get_type_bias): New.
	(LANG_HOOKS_GET_TYPE_BIAS): Redefine macro to implement the
	get_type_bias language hook.

gcc/ChangeLog:

	* langhooks.h (struct lang_hooks_for_types): New get_bias_field.
	* langhooks-def.h (LANG_HOOKS_GET_TYPE_BIAS): New.
	(LANG_HOOKS_FOR_TYPES_INITIALIZER): Initialize the
	get_bias_field.
	* dwarf2out.c
	(base_type_die): In non-strict DWARF mode, invoke the
	get_type_bias language hook for INTEGER_TYPE nodes.  If it
	returns a bias, emit an attribute for it.
	(subrange_type_die): Change signature to handle bias.  If
	non-strict DWARF mode, emit an attribute for it, if one passed.
	(modified_type_die): For subrange types, invoke the
	get_type_bias langage hook and pass the bias to
	subrange_type_die.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@231767 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 5 insertions, 0 deletions

diff --git a/gcc/langhooks.h b/gcc/langhooks.h
index f84bdf64bf4..95d5840d0a9 100644
--- a/gcc/langhooks.h
+++ b/gcc/langhooks.h
@@ -127,6 +127,11 @@ struct lang_hooks_for_types
   /* Fill in information for the debugger about the bounds of TYPE.  */
   void (*get_subrange_bounds) (const_tree, tree *, tree *);
 
+  /* Called on INTEGER_TYPEs.  Return NULL_TREE for non-biased types.  For
+     biased types, return as an INTEGER_CST node the value that is represented
+     by a physical zero.  */
+  tree (*get_type_bias) (const_tree);
+
   /* A type descriptive of TYPE's complex layout generated to help the
      debugger to decode variable-length or self-referential constructs.
      This is only used for the AT_GNAT_descriptive_type DWARF attribute.  */