[trunk] Addition to subreg section of rtl.text.

[Richard Kenner]

> That's my understanding too as far as insn operands are concerned.
> But some backends use things like "(subreg (match_operand ...) ...)";
> see config/rs6000/spe.md for an example.  We need to define what those
> subregs mean when the inner register has been reloaded.
> 
> Or I suppose we could say that such define_insns are in error and
> use another construct instead.

I would consider such things dubious at best.  I'm kind of surprised
they work.