On Wed, Mar 11, 2009 at 08:33:34AM +0100, Georg-Johann Lay wrote:
> Stelian Pop schrieb:
>> On Tue, Mar 10, 2009 at 10:18:10PM +0100, Georg-Johann Lay wrote:
>>
>>
>>> Note that no one is generating an insn that looks like "*jump". Maybe
>>> insn combine and peep2 would try to build such a pattern, but that
>>> is not what helpd you out here. Write the expander as parallel of a
>>> (set (pc) ...) and a (clobber (match_scratch ...)) so that an
>>> appropriate insn is expanded.
>>
>>
>> Like this ?
>>
>> (define_expand "jump"
>> [(parallel [(set (pc) (label_ref (match_operand 0 "" "")))
>> (clobber (match_scratch:QI 1 "=&r"))])]
>> ""
>> ""
>> )
>
> Constraints are useless in expanders.
Of course, copy'n'paste error.
> You really need a QI scratch? Your
> insn looks as if HI was needed as you load hi and lo part of the scratch.
Yes, QI is correct: my microcontroller is a bit special in that in has
16 bit bytes (BITS_PER_UNIT=16).
[...]
> So you have just one alternative "=&r", and in the case of rjmp the
> scratch is unused.
Ok, so I ended up with (omitting the jump lengths for now):
(define_insn "*jump"
[(set (pc)
(label_ref (match_operand 0 "" "")))
(clobber (match_scratch:QI 1 "=&r"))]
""
{
return "ldih %1,hi(%l0)\n\t\n\tldil %1,lo(%l0)\n\tijmp (%1)";
}
)
(define_expand "jump"
[(parallel [(set (pc) (label_ref (match_operand 0 "" "")))
(clobber (match_scratch:QI 1 ""))])]
""
""
)
It doesn't work. It causes a loop somewhere in gcc. I can get a gdb
trace if needed.
> Note that you emit up to three instructions, so the
> -2048/2047 may crash in corner cases.
Right, thanks !
> You can have a look at avr, it computes jump lengths as well but afaIr
> without needing a scratch for long jumps.
I'll do. I'm trying now first to get the indirect jump to work, and I'll
put the test for the jumps lenghts later.
Thanks,
--
Stelian Pop <[email protected]>
