On 09/02/2011 04:53 AM, Richard Guenther wrote:
On Thu, Sep 1, 2011 at 5:19 PM, Jason Merrill<ja...@redhat.com> wrote:
I think it would make sense to expose this information to the back end
somehow. A hook would do the trick: call it type_data_size or type_min_size
or some such, which in the C++ front end would return TYPE_SIZE
(CLASSTYPE_AS_BASE (t)) for classes or just TYPE_SIZE for other types.
That's too late to work with LTO, you'd need to store that information
permanently somewhere.
OK.
Maybe move this whole C++ specific bitfield handling where it belongs,
namely to the C++ frontend?
I don't think that is the way to go; C is adopting the same memory
model, and this is the only sane thing to do with bit-fields.
I suggest to always not re-use tail padding for now (I believe if your
parent object is a COMPONENT_REF, thus, x.parent.bitfield,
you can use the TYPE_SIZE vs. field-decl DECL_SIZE discrepancy
to decide about whether the tail-padding was reused, but please
double-check that ;)))
But you don't always have a COMPONENT_REF; you still need to avoid
touching the tail padding when you just have a pointer to the type
because it might be a base sub-object.
I wonder what would break if C++ just set TYPE_SIZE to the as-base size?
Jason
