Re: Fix powerpc-linux gcc.dg/20020103-1.c

[Geoff Keating <geoffk at geoffk dot org>]

On 04/11/2004, at 5:19 PM, Alan Modra wrote:

> On Thu, Nov 04, 2004 at 12:10:25PM -0800, Geoff Keating wrote:
> > Alan Modra <amodra@bigpond.net.au> writes:
> > > Ping!  http://gcc.gnu.org/ml/gcc-patches/2004-10/msg02570.html
> >
> > I don't think this patch is the right direction.  You're working
> > around reload in the backend.
>
> Not really.  I'm delaying generation of unspec rtl that generic code
> can't handle.  Surely that is a good thing, as it fits in with the
> philosophy of keeping target dependent wrinkles out of intermediate
> representations as long as possible.  As demonstrated by the fact that
> this change allows us to generate ideal code without further
> complicating reload with target dependent information.

You're hiding information from earlier passes in the compiler, which is 
not a good thing.

> Of course, that argument fails if you really need the unspec early.
> I'm reasonably confident we don't.  As far as I can tell,
> unspec_movsi_got was a half-baked attempt to reserve r30 early
> enough so that r30 was free to use if a function didn't make any got
> accesses.  True?

I'm not sure why it had to be an unspec.  However, it would be a really 
good thing if we could arrange that r30 could be used by functions that 
don't need the got.

> >  Instead, you should teach reload how to
> > load from a SYMBOL_REF.  I believe this is just a change to
> > rs6000_emit_move.
>
> I looked at changing reload before taking the approach I did.  It's not
> quite as simple as you indicate, ie. more than just rs6000_emit_move
> needs changing, I think.

What problems did you find?

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