On Tue, Jan 09, 2024 at 10:39:50AM +0100, Richard Biener wrote:
> > x86 can't combine IOR/XOR in any meaningful way, but can combine the
> > sequence of PLUS (together with MULT) RTXes to LEA.
>
> Btw, this looks like a three-insn combination even with IOR so a
> pattern for this case would work as well?
>
> Deciding whether to use PLUS or IOR at RTL expansion time would
> need to somehow figure out what's better for the target in question.
> I'm not sure how to do that?
Maybe a new optab which would be used when expanding
BIT_IOR_EXPR/BIT_XOR_EXPR with operands which have no common bits
(say in (get_nonzero_bits (arg1) & get_nonzero_bits (arg2)) == 0
sense)?
x86 and riscv could just emit a PLUS in those cases...
Jakub
