RFA: reload infrastructure to fix PR target/21623

[Kaz Kojima]

Joern RENNECKE <joern.rennecke@st.com> wrote:
> Yes.  This patch is OK for mainline and any open release branches, as it 
> makes
> cost calculations more accurate.  However, the PR should stay open till 
> we can
> express the required reloads.

Indeed.

Could you give me a hint about how the cost should be estimated?
I'm not able to find pointers for it except a brief description
of REGISTER_MOVE_COST in doc/tm.texi.

Regards,
	kaz