The change to "assignment not used" breaks symmetry with
"used and not set" and removes the reference to the
specific warning mentioned in /sys/doc/comp.ms.
Also, the patch was half-assed as that it left some typos
in like "used an not set", which this change also fixed.
we have to explicitely convert to vlong by sign or
zero extending as not every operation leaves a proper
zero/sign extended result in the register. for example
NEGW will zero extend, breaking negative int offsets
on pointers.
we explicitely insert SXTW or MOVWU instructions which
the peephole optimizer takes out again when it is safe
todo so.
when promoting constant offsets to immediate offsets,
make sure the offset will be in range. otherwise the
linker will produce not so optimal pointer arithmetic
instructions to calculate the offset.
