[PATCH] DATA_ALIGNMENT vs. DATA_ABI_ALIGNMENT (PR target/56564)

[Jakub Jelinek]

On Fri, Jun 07, 2013 at 06:56:34PM -0400, Hans-Peter Nilsson wrote:
> > cris	compiler options for alignment -- systemwide or local?
> 
> No, DATA_ALIGNMENT in cris.h is not intended as an ABI
> indication, but as an optimization when emitting data.
> (This was the way to do it at the time.  Has this changed?)
> 
> The ABI is as indicated by BIGGEST_ALIGNMENT: 8 (bits; one
> byte).  Nothing is guaranteed (to the data referer) to have a
> bigger alignment - unless otherwise indicated by attribute-align.
> 
> (Unfortunately I can't change BIGGEST_ALIGNMENT to indicate that
> atomic variables require "natural alignment", or actually not to
> straddle a cache-boundary, as increasing BIGGEST_ALIGNMENT makes
> GCC change the ABI.  But that's a slightly different issue.)

Right now it is unfortunately part of ABI, which is something the patch
attempts to cure in a backwards compatible way (i.e., data will be still
alignment the way it used to be, but code will no longer assume it is that
much aligned, unless it is DATA_ABI_ALIGNMENT).
> 
> > mmix	comment mentions GETA instruction
> 
> Yep, data must be at least 32-bit-aligned so addresses can be
> formed with a GETA insn.  BIGGEST_ALIGNMENT is 64 though and
> STRICT_ALIGNMENT; natural alignment is required for proper
> interpretation as the low bits are ignored.

Then mmix would probably want to define DATA_ABI_ALIGNMENT instead of
DATA_ALIGNMENT after the patch (or both).

	Jakub