Convert the unavailable vector to be bit, not byte, based.

  https://sourceware.org/ml/gdb-patches/2013-12/msg00144.html

The vector of unavailable parts of a value is currently byte based.  Given
that we can model a value down to the bit level, we can potentially loose
information with the current implementation.  After this patch we model the
unavailable information in bits.

gdb/ChangeLog

	* dwarf2loc.c (read_pieced_value): Mark bits, not bytes
	unavailable, use correct bit length.
	* value.c (struct value): Extend comment on unavailable to
	indicate that it is bit based.
	(value_bits_available): New function.
	(value_bytes_available): Call value_bits_available.
	(value_entirely_available): Check against the bit length, not byte
	length.
	(mark_value_bits_unavailable): New function.
	(mark_value_bytes_unavailable): Move contents to
	mark_value_bits_unavailable, call to same.
	(memcmp_with_bit_offsets): New function.
	(value_available_contents_bits_eq): New function, takes the
	functionality from value_available_contents_eq but uses
	memcmp_with_bit_offsets now, and is bit not byte based.
	(value_available_contents_eq): Move implementation into
	value_available_contents_bits_eq, call to same.
	(value_contents_copy_raw): Work on bits, not bytes.
	(unpack_value_bits_as_long_1): Check availability in bits, not
	bytes.
	* value.h (value_bits_available): Declare new function.
	(mark_value_bits_unavailable): Declare new function.

gdb/testsuite/ChangeLog

	* gdb.trace/unavailable-dwarf-piece.c: New file.
	* gdb.trace/unavailable-dwarf-piece.exp: New file.

1 files changed, 14 insertions, 0 deletions

diff --git a/gdb/value.h b/gdb/value.h
index db964e36e83..6b158df1933 100644
--- a/gdb/value.h
+++ b/gdb/value.h
@@ -436,6 +436,14 @@ extern int value_bits_synthetic_pointer (const struct value *value,
 extern int value_bytes_available (const struct value *value,
 				  int offset, int length);
 
+/* Given a value, determine whether the contents bits starting at
+   OFFSET and extending for LENGTH bits are available.  This returns
+   nonzero if all bits in the given range are available, zero if any
+   bit is unavailable.  */
+
+extern int value_bits_available (const struct value *value,
+				 int offset, int length);
+
 /* Like value_bytes_available, but return false if any byte in the
    whole object is unavailable.  */
 extern int value_entirely_available (struct value *value);
@@ -450,6 +458,12 @@ extern int value_entirely_unavailable (struct value *value);
 extern void mark_value_bytes_unavailable (struct value *value,
 					  int offset, int length);
 
+/* Mark VALUE's content bits starting at OFFSET and extending for
+   LENGTH bits as unavailable.  */
+
+extern void mark_value_bits_unavailable (struct value *value,
+					 int offset, int length);
+
 /* Compare LENGTH bytes of VAL1's contents starting at OFFSET1 with
    LENGTH bytes of VAL2's contents starting at OFFSET2.