More primops for integer arithmetic with overflow reporting

[Herbert Valerio Riedel]

Hello GHC HQ,

As the {Int,Word}{,8,16,32,64} types in Haskell are usually regarded to
follow modulo arithmetic (w.r.t. to the Num-class ops), I was trying to
implement efficient non-modulo Safe{Int,Word}{,8,16,32,64} types which
would throw exceptions when the result falls outside the value domain
representable.

As ISAs often have hardware support to detect such overflows (e.g. on
x86-64 via the OF/CF flags), I guess that by exploiting hardware
support, this might allow for a reasonably efficient implementation of
non-modulo integer arithmetic.

So far I've only found 'addIntC#' and 'subIntC#' which perform the kind
of operation I'm looking for. But this is only for signed integers, and
as far as multiplication is concerned, there's a 'mulIntMayOflo#' but
that may provide false negatives according to the documentation.

Therefore, I was wondering whether it'd make sense for GHC to provide
more primops for the {Int,Word}{,8,16,32,64} types which return the
result value together with an overflow-flag.

Thanks,
hvr