Re: [PATCH] LRA: Fix caller-save store/restore instruction for large mode

[Vladimir Makarov <vmakarov at redhat dot com>]

On 2015-01-05 12:31 PM, Jeff Law wrote:
> On 01/05/15 00:44, Kito Cheng wrote:
> > Hi Vladimir:
> >    This patch has a discusses with you in May 2014, this patch is about
> > the caller-save register store and restore instruction generation, the
> > current LRA implementation will miss caller-save store/restore
> > instruction if need one more instruction.
> >
> > You said you will investigate for this on IRC, so I don't send the
> > patch last year, however ARM guys seem got this problem too, so I
> > think it's time to send this patch :)
> >
> > ChangeLog
> >
> > 2015-01-05  Kito Cheng  <kito@0xlab.org>
> >
> >          * lra-constraints.c (split_reg): Fix caller-save store/restore
> > instruction generation.
> Please reference PR64348 in the ChangeLog entry.
>
> Please include a testcase if there isn't one in the regression suite 
> already.
>
> Please indicate what platform this patch was bootstrapped and 
> regression tested on.
>
> The dumping code immediately after the assert you removed has code 
> like this in both cases:
>
>
>
>          fprintf (lra_dump_file,
>                    "    Rejecting split %d->%d "
>                    "resulting in > 2 %s restore insns:\n",
>                    original_regno, REGNO (new_reg), call_save_p ? 
> "call" : "");
>
> Testing call_save_p here won't make any sense after your patch.
>
> I'll let Vlad chime in on the correctness of allowing multi register 
> saves/restores in this code.
The solution itself is ok.  Prohibiting generation of more one insn was 
intended for inheritance only as inheritance transformation can be 
undone when the inheritance pseudo does not get a hard register. Undoing 
multi-register splitting is difficult and also such splitting is 
doubtedly profitable.

Splitting for save/restore is never undone.  So it is ok for this case 
to generate multi-register saves/restores.

Kito, Jeff wrote reasonable changes for the patch.  Please, do them and 
you can commit the patch.

Thanks.