On Tue, Mar 10, 2009 at 05:20:28PM +0000, Dave Korn wrote:
> Stelian Pop wrote:
>
> > I need to use a scratch register in the "jump" pattern and I can't
> > figure out how to do it properly.
> >
> > My problem is that the microcontroller I'm porting gcc onto does not
> > permit "far" jumps, those must be done using an indirect adressing.
>
> > (define_insn "*jump"
>
> > Any idea ?
>
> You should be able to define/use the "indirect_jump" pattern instead? Take
> a look at the last paragraph of the the docs for the "call" pattern as well.
>
I already do have an "indirect_jump" pattern in my md file:
(define_insn "indirect_jump"
[(set (pc)
(match_operand:QI 0 "register_operand" "r"))]
""
"ijmp (%0)"
[(set_attr "cc" "none")]
)
However, I didn't find a way to say to gcc that it cannot use the "direct"
jump in some cases, and force it to use the "indirect_jump" instead.
> I don't think it'll work to have a jump insn that is sometimes direct,
> sometimes indirect.
> Looking at how the rs6000 backend handles direct and indirect calls and
> jumps might give you some inspiration too.
Well, I already did look at all the backends, but didn't find the answer
(although the answer probably is hidden somewhere inside those files...).
As for the rs6000 backend I see a simple direct call pattern, not sure what
you want me to look at:
in rs6000.md:
(define_insn "jump"
[(set (pc)
(label_ref (match_operand 0 "" "")))]
""
"b %l0"
[(set_attr "type" "branch")])
Thanks,
Stelian.
--
Stelian Pop <stel...@popies.net>
