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Re: new port: msp430-elf
- From: Richard Sandiford <rsandifo at linux dot vnet dot ibm dot com>
- To: DJ Delorie <dj at redhat dot com>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Thu, 09 May 2013 10:06:24 +0100
- Subject: Re: new port: msp430-elf
- References: <201305070241 dot r472fQp5022965 at greed dot delorie dot com> <CABu31nO5sXW6qT8QNPDKGj41N6scFct7KZPmYiQ1pCA2unm-bg at mail dot gmail dot com> <201305080045 dot r480jAVE028590 at greed dot delorie dot com> <87y5bpomb7 dot fsf at sandifor-thinkpad dot stglab dot manchester dot uk dot ibm dot com> <201305082149 dot r48LnLLB021495 at greed dot delorie dot com>
DJ Delorie <dj@redhat.com> writes:
>> It looks like the patch also treats PSImode->SImode as a truncation though.
>
> I'd have to check specifically for partial_int_mode, since there's
> nothing in PARTIAL_INT_MODE() to set the precision, unless there's
> some other way to set PSImode's bits *and* reliably use that info.
Right. At some point we're going to have to bite the bullet and model
partial modes properly :-) Sounds like Mike might have some patches for that.
>> BTW, if SImode->PSImode is so expensive, MODES_TIEABLE_P should probably
>> return false for that pair of modes. That'll discourage -- but not prevent --
>> the rtl optimisers from replacing (reg:PSI ...) operands with
>> (subreg:PSI (reg:SI ...)) ones.
>
> I'll try that. Thanks!
>
> Hmmm... psi/si in memory are tieable, psi/si in registers
> aren't... what's the right thing to do here?
I think we assume everything is tieable in memory. MODES_TIEABLE_P says
whether we should assume that a pseudo register in one mode can be
accessed in another mode without triggering some kind of copy operation.
Thanks,
Richard