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Re: RFA: autoincrement patches for gcc 4 - updated patch
Richard Henderson wrote:
On Tue, May 17, 2005 at 12:29:04PM +0200, Bernd Schmidt wrote:
Ugh. I worked on this code back when I was at Red Hat, and as far as I
recall it never worked correctly in any of its incarnations. Also, the
cost estimates are pretty sh specific.
Do you have specific concerns?
First off, I can no longer reproduce the failures I saw a while ago with
an earlier version of this patch, so it seems to have improved somewhat.
I still have a few concerns though.
The way it re-uses existing pseudo reg numbers has proven to be
extremely brittle; it's very easy to get confused about the lifetimes.
I'd prefer an approach that just allocates new pseudos - we seem to have
the ability now to turn off no_new_pseudos temporarily, and we might as
well use it.
As far as sh-specific assumptions go, it assumes that adds are 2-address
insns, and it does not take into account machines with more addressing
modes - it doesn't try to generate or modify offsetted addresses as far
as I can see or remember. Neither does it try to use post-modify for
machines that have it.
The way I see it, Joern is pretty much the only person willing to care
about auto-increment optimization, since it touches so few of our targets.
I need something quite similar to this pass for the Blackfin, but as it
stands it doesn't have much of an effect since the Blackfin has
different needs than the sh.
A few weeks ago I've started working on a reimplementation of something
like this. Admittedly it's mostly vapourware right now and shouldn't
hold up this patch if it is technically sound - I just don't believe
that it is.