s390 port

[Jakub Jelinek]

On Fri, Sep 03, 2021 at 10:38:36PM +1000, Paul Edwards via Gcc wrote:
> > This is not in one single place, but spread throughout the
> > compiler, both common code and back-end.  I do not think it will
> > be possible to get the compiler to generate correct code if
> > you do not specify the address size correctly.
> 1. Is there any way to put a constraint on index
> registers, to say that a particular machine can
> only index in the range of –512 to +512 or some
> other arbitrary set? If so, I can do 0 to 2 GiB.
> 2. Is there a way of saying a machine doesn’t
> support indexing at all?

There is a way to do that, but it isn't about changing a single or a couple
of spots, one needs to change a lot of *.md patterns, a lot of macros,
target hooks and as Ulrich said, most important is to use the right Pmode
which can differ from ptr_mode provided one e.g. defines ptr_extend pattern
etc.
Just look at the amount of work needed for the x32 or aarch64 ilp32 support,
and not just work spent one time on adding that support, but the continuous
amount of work on maintaining it.  The initial work is certainly a few
weeks if not months of work, then there needs to be somebody who regularly
tests gcc trunk and branches in such configuration so that it doesn't
bitrot, and not just that but somebody who actually fixes bugs in it.

If something doesn't fit into 2GB of address space, isn't it likely it won't
fit into 4GB of address space in a year or two?

	Jakub