define_split

[roy rosen]

Hi all,

I am trying to use define_split, but it seems to me that I don't
understand how it is used.
It says in the gccint.pdf (which I use as my tutorial (is there
anything better or more up to date?)) that the combiner only uses the
define_split if it doesn't find any define_insn to match. This is not
clear to me: If there is no define_insn to match a pattern in the
combine stage, then how is this pattern there in the first place? The
only way I can think for it to happen is that such a pattern was
created by the combiner itself (but it seems unreasonable to me that
we now want to split what the combiner just combined). Can someone
please explain this to me?

Thanks, Roy.