making sizeof(void*) different from sizeof(void(*)())

[Peter Bigot <bigotp at acm dot org>]

The MSP430's split address space and ISA make it expensive to place
data above the 64 kB boundary, but cheap to place code there.  So I'm
looking for a way to use HImode for data pointers, but PSImode for
function pointers.  If gcc supports this, it's not obvious how.

I get partway there with FUNCTION_MODE and some hacks for the case
where the called object is a symbol, but not when it's a
pointer-to-function data object.  As an example, bootstrapping fails
in libgcc/unwind-dw2-fde.c because the fde_compare pointer-to-function
object is stored in a HImode register instead of a PSImode register.

The only candidate solution I've seen (and haven't yet tried) is to
somehow assign all functions to be in a special named address space
and use TARGET_ADDR_SPACE_POINTER_MODE to override the normal use of
ptr_mode in build_pointer_type.

I haven't been able to identify an existing back-end that has such a
case, though I'd swear I've seen memory models like this for some
other processor in the past.

Could somebody suggest a workable solution for 4.7.x?

Thanks.

Peter