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Date: Wed, 15 Jul 2015 13:25:00 -0000
From: Michael Matz <matz@suse.de>
To: Jim Wilson <jim.wilson@linaro.org>
cc: Richard Earnshaw <Richard.Earnshaw@foss.arm.com>,     Richard Biener <richard.guenther@gmail.com>, Jeff Law <law@redhat.com>,     "gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH, ARM] stop changing signedness in PROMOTE_MODE
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Hi,

On Tue, 14 Jul 2015, Jim Wilson wrote:

> Now that we do have the problem, we can't fix it without an ARM port ABI 
> change, which is undesirable, so we may have to fix it with a MI change.

What's the ABI implication of fixing the inconsistency?

> There were two MI changes suggested, one was fixing the out-of-ssa pass 
> to handle SUBREG_PROMOTED_P promotions.  The other was to disallow 
> creating PHI nodes between parms and locals.  I haven't had a chance to 
> try implementing the second one yet; I hope to work on that today.

Don't bother with the latter, it doesn't have a chance of being accepted.

If the terrible hack in outof-ssa really will be necessary (and I really 
really hope it won't) then I think I prefer the approach you partly tried 
in comment #12 of PR 65932 already.  Let partition_to_pseudo[] refer to 
the promoted subreg and deal with that situation in emit_partition_copy; 
I'd then hope that the unsignedsrcp parameter could go away (unfortunately 
the sizeexp will have to stay).


Ciao,
Michael.