> It is nicely generic as well, but requires more insns than this if your
> ISA does not have a full complement of logical ops. Well, just an
> "andnot" is enough, you don't actually need eqv here.
Indeed, and it's rather spectacular for 64-bit operations on 32-bit machines
because the sign bit trick can be done solely on the upper word, whereas a
fully-fledged store-flag sequence is heavyweight in this case. Here's what
the patched generic code yields at -O2:
op__add32:
add 10,3,4
xor 9,10,4
eqv 4,3,4
and. 8,9,4
blt- <overflow>
mr 3,10
blr
op__add64:
addc 4,4,6
adde 10,3,5
xor 9,10,5
eqv 5,3,5
and. 8,9,5
blt- <overflow>
mr 3,10
blr
This should help 32-bit x86 too, which doesn't have 64-bit operations AFAICS.
Thanks for the tip, I'll submit the change to the generic code separately.
--
Eric Botcazou
