On Thu, Apr 12, 2018 at 05:17:29PM +0200, Richard Biener wrote:
> >For -Os that is easily measurable regression, for -O2 it depends on the
> >relative speed of memcpy vs. mempcpy and whether one or both of them
> >are in
> >I-cache or not.
>
> Well, then simply unconditionally not generate a libcall from the move
> expander?
We need to generate libcall for many callers and in fact, we don't have a
mode nor a way to tell the caller that we haven't emitted anything.
What we could do is add another enumerator to enum block_op_methods that
would be like BLOCK_OP_NO_LIBCALL, but would not use emit_block_move_via_loop
if move_by_pieces nor emit_block_move_via_movmem can be used, and say
instead return const0_rtx or pc_rtx or some way to tell the caller that
it hasn't emitted anything and in expand_builtin_memory_copy_args
pass for endp == 1 && target != const0_rtx that new BLOCK_OP_NO_LIBCALL_LOOP
to emit_block_move_hints and return 0 if dest_addr is const0_rtx (or pc_rtx
or whatever is chosen).
Jakub
