AW: [PATCH] m68k architecture: support ccmode + lra

[Richard Biener]

On December 12, 2019 7:43:58 AM GMT+01:00, Stefan Franke <stefan@franke.ms> wrote:
>Am 2019-12-08 01:54, schrieb Oleg Endo:
>> On Tue, 2019-11-26 at 07:38 +0100, stefan@franke.ms wrote:
>>> > On 11/21/19 10:30 AM, stefan@franke.ms wrote:
>>> > > Hi there,
>>> > >
>>> > > here is mc68k's patch to switch the m68k architecture over to
>ccmode
>>> > > and
>>> > > lra. See https://github.com/mc68kghost/gcc 68k-ccmode branch.
>>> >
>>> > Bernd Schmidt posted a conversion of the m68k port to ccmode a
>couple
>>> > weeks before yours.  We've already ACK'd it for installing onto
>the
>>> > trunk.
>>> >
>>> > Jeff
>>> 
>>> To be honest:
>>> - 8 days is hardly "a couple weeks before"
>>> - ccmode is not the same as ccmode+lra
>>> 
>>> The paperwork for contributing to fsf is on the way and the repo at
>>> https://github.com/mc68kghost/gcc got an update. Tests are not yet
>at 
>>> 100%
>>> (master branch fails too many tests) but it's closer to master
>branch 
>>> now.
>>> The code is to 50% identical, a fair amount has swapped cmp/bcc, few
>
>>> are a
>>> tad worse and some yield surprisingly better code.
>>> 
>> 
>> You can still submit patches for further improvements, like adding
>> support for LRA.  Now that the main CCmode conversion is on trunk and
>> has been confirmed and tested, it should be much easier for you to
>> pinpoint problems in your changes.
>> 
>> Cheers,
>> Oleg
>
>The problems are in the gcc implementation
>
>- the lra implementation is buggy
>- the compare elimination can't handle parallel's containing a compare
>- df-core considers parallel's containing a compare also as a USE
>- some optimizations/mechanisms do only work if HAVE_CC0 is defined
>- way more ...
>
>And the current implementation is IMHO unusable for lra since it did
>not 
>introduce a CC register to track clobbering. So it's a dead end.
>
>I can live with the fact that my patch was refuted since I simply use
>my 
>*working* fork, where I fixed the issues mentioned above.

You can of course also submit those changes. I think the work that got in was the minimal work required to get the target off CC0. 

Richard. 

>/cheers
>Stefan