dead label use?

dead label use?

[Mike Stump]

Forgive me ignorance, is there is use for the use of the label below?

 From rs6000, though, certainly there are other examples of this sort of 
thing in the md files:

(define_insn ""
   [(set (pc)
         (match_operand:P 0 "register_operand" "c,*l"))
    (use (label_ref (match_operand 1 "" "")))]
   ""
   "@
    bctr
    {br|blr}"
   [(set_attr "type" "jmpreg")])

Re: dead label use?

[Ian Lance Taylor]

Mike Stump <mrs@apple.com> writes:

> Forgive me ignorance, is there is use for the use of the label below?
> 
>  From rs6000, though, certainly there are other examples of this sort
> of thing in the md files:
> 
> (define_insn ""
>    [(set (pc)
>          (match_operand:P 0 "register_operand" "c,*l"))
>     (use (label_ref (match_operand 1 "" "")))]
>    ""
>    "@
>     bctr
>     {br|blr}"
>    [(set_attr "type" "jmpreg")])

This is an instantiation of a tablejump created via define_expand.
Operand 1 is the jump table.  The insn needs to refer to it, or the
table will be deleted as unreferenced.

Ian

Re: dead label use?

[Geoffrey Keating]

Ian Lance Taylor <ian@airs.com> writes:

> Mike Stump <mrs@apple.com> writes:
> 
> > Forgive me ignorance, is there is use for the use of the label below?
> > 
> >  From rs6000, though, certainly there are other examples of this sort
> > of thing in the md files:
> > 
> > (define_insn ""
> >    [(set (pc)
> >          (match_operand:P 0 "register_operand" "c,*l"))
> >     (use (label_ref (match_operand 1 "" "")))]
> >    ""
> >    "@
> >     bctr
> >     {br|blr}"
> >    [(set_attr "type" "jmpreg")])
> 
> This is an instantiation of a tablejump created via define_expand.
> Operand 1 is the jump table.  The insn needs to refer to it, or the
> table will be deleted as unreferenced.

The problem is that the table has to be referenced *from a jump_insn*,
I think.  Obviously if the table is really unreferenced it could be deleted.