Re: defining add in a new port

[Jean-Marc Saffroy <jean-marc dot saffroy at joguin dot com>]

On 01/28/2011 06:44 PM, Ian Lance Taylor wrote:
> Jean-Marc Saffroy <jean-marc.saffroy@joguin.com> writes:
> 
>> error: insn does not satisfy its constraints:
>> (insn 1424 1423 141 (set (reg:DI 2 r2)
>>         (plus:DI (reg:DI 2 r2)
>>             (const_int 40 [0x28])))
>> /home/jmsaffroy/cygnus/src/newlib/libc/time/strptime.c:165 24 {adddi3}
>>      (expr_list:REG_EQUIV (plus:DI (reg/f:DI 70 a6)
>>             (const_int 40 [0x28]))
>>         (nil)))
> 
> You should find out what is creating this insn.  Is it being created by
> reload, or is it being created by some pass that runs after reload?

With gcc -da, I see that it appears in dump .195r.ira, so that's reload,
right?

> It is likely that you need to make adddi3 a define_expand which tests
> reload_in_progress and reload_completed.  If those are the case, you
> will need to explicitly convert
>     (set (reg:DI DREG1) (plus:DI (reg:DI DREG2) (const_int N)))
> into
>     (set (reg:DI DREG1) (const_int N))
>     (set (reg:DI DREG1) (plus:DI (reg:DI DREG1) (REG:DI DREG2)))
> 

Ah, but here it happens that DREG1 and DREG2 (r2 and a6 above) are
different types of registers, and I can't add them directly. And since
at this point I won't be allowed to allocate any reg (right?), I guess I
will have to do something like:

(set DREG2 (plus DREG2 N))
(set DREG1 DREG2)
(set DREG2 (plus DREG2 -N))

And that only works if N isn't too big for adds with DREG2. I hope it
will turn out to be an uncommon case, or can be optimized away in
subsequent passes.

> For a much more sophisticated version of this, see, e.g., addsi3 in the
> ARM target.
> 
> Ian
> 

Ok, I'll look into it.

Thanks a lot!


JM