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Re: [PATCH RFC] Finer grained reg classes.
- From: Steven Bosscher <stevenb dot gcc at gmail dot com>
- To: David Miller <davem at davemloft dot net>
- Cc: Ian Lance Taylor <iant at google dot com>, gcc-patches <gcc-patches at gcc dot gnu dot org>, Eric Botcazou <ebotcazou at adacore dot com>, rth at twiddle dot net, Jeff Law <law at redhat dot com>
- Date: Tue, 19 Mar 2013 20:17:09 +0100
- Subject: Re: [PATCH RFC] Finer grained reg classes.
- References: <20130319 dot 113349 dot 779301153261368350 dot davem at davemloft dot net> <CAKOQZ8z1gtyMowAu--nXkU83imQRL=M0rA3Hr4hdbONNXRE2sg at mail dot gmail dot com> <5148AEE9 dot 6060903 at redhat dot com>
On Tue, Mar 19, 2013 at 7:31 PM, Jeff Law wrote:
> On 03/19/2013 11:58 AM, Ian Lance Taylor wrote:
>>
>> On Tue, Mar 19, 2013 at 8:33 AM, David Miller wrote:
>>>
>>>
>>> So this patch tries to rework the semantics of hard register classes,
>>> such that if a hard register is present in the set it is implied that
>>> the rest of the registers in a multi-register group are present as
>>> well. So we can add a register class called EVEN_REGS and only have
>>> to set the even register bits.
>>
>>
>> I haven't really looked at your patch, but I just want to say that I
>> think this is the right way to go.
>
> Likewise. I've certainly worked on ports where this would have been helpful
> in the past.
It could also help simplify existing ports. rs6000 has a few places
where this could be useful (dfp). At least arm
(VFP_REGNO_OK_FOR_DOUBLE), avr, and h8300, too. And ISTR s390 plays
funny subreg tricks to get this right. Finally, it's been discussed on
the gcc@ mailing list for out-of-tree ports a few times in recent
history.
So yes, great if this can be done!
Ciao!
Steven