Expansion of narrowing math built-ins into power instructions

[Martin Jambor]

Hi Segher,

as you might know, Tejas is our Google Summer of Code student working on
adding built-in functions for some new math functions added in ISO/IEC
TS 18661.

His next step is to expand "functions rounding result to narrower type"
(so fadd, fsub and possibly fmul and fdiv described in
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2314.pdf) into ISA
instructions on targets that have such instructions.  And Joseph
suggested when he proposed this project that POWER8 (and I suppose also
9) is one of them.

Can you please confirm this and also perhaps point Tejas to the right
pieces of power machine description and target code to emulate to
implement expansion of these functions?  It would be very appreciated,
because even though me and Honza are official mentors of the project, we
are not very well versed in ppc target.

Thanks a lot,

Martin