[Ada] Fix and improve record packing

[Eric Botcazou]

This patch lifts an old limitation of the compiler: components of packed 
arrays or records that are not bit-packed are not packed, i.e. their size
is not made smaller than that of their type.  This is all the more annoying 
that a component size clause corresponding to the theoritical packed size is 
accepted and, consequently, not honored.

Conversely, if a component of a packed record is bit-packed and happens to be 
of a record type itself, accessing inner fields within the outer record may 
overrun the component.  This is fixed by locally rewriting the type.

Finally, the patch makes it possible for a component size clause on an array 
type to override the type size of the component.

Tested on i586-suse-linux, applied on the mainline.


2008-03-07  Eric Botcazou  <ebotcazou@adacore.com>

	* decl.c (MAX_FIXED_MODE_SIZE): Define if not already defined.
	(gnat_to_gnu_entity) <E_Record_Type>: Try to get a smaller form of
	the component for packing, if possible, as well as if a component
	size clause is specified.
	<E_Record_Subtype>: For an array type used to implement a packed
	array, get the component type from the original array type.
	Try to get a smaller form of the component for packing, if possible,
	as well as if a component size clause is specified.
	(round_up_to_align): New function.
	(make_packable_type): Add in_record parameter.
	For a padding record, preserve the size.  If not in_record and the
	size is too large for an integral mode, attempt to shrink the size
	by lowering the alignment.
	Ditch the padding bits of the last component.
	Compute sizes and mode manually, and propagate the RM size.
	Return a BLKmode record type if its size has shrunk.
	(maybe_pad_type): Use MAX_FIXED_MODE_SIZE instead of BIGGEST_ALIGNMENT.
	Use Original_Array_Type to retrieve the type in case of an error.
	Adjust call to make_packable_type.
	(gnat_to_gnu_field): Likewise.
	(concat_id_with_name): Minor tweak.
	* trans.c (larger_record_type_p): New predicate.
	(call_to_gnu): Compute the nominal type of the object only if the
	parameter is by-reference.  Do the conversion actual type -> nominal
	type if the nominal type is a larger record.
	(gnat_to_gnu): Do not require integral modes on the source type to
	avoid the conversion for types with identical names.
	(addressable_p): Add gnu_type parameter.  If it is specified, do not
	return true if the expression is not addressable in gnu_type.
	Adjust recursive calls.
	* utils.c (finish_record_type): Remove dead code.


2008-03-07  Eric Botcazou  <ebotcazou@adacore.com>

        * gnat.dg/pack3.adb: New test.

-- 
Eric Botcazou
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