On 10/18/17 15:46, Segher Boessenkool wrote: > On Wed, Oct 18, 2017 at 06:30:23AM -0500, Segher Boessenkool wrote: >> On Wed, Oct 18, 2017 at 11:10:48AM +0000, Bernd Edlinger wrote: >>> A memory clobber would also make rtx_moveable_p return false, >>> thru the following case: >>> >>> case MEM: >>> if (type == OP_IN && MEM_READONLY_P (x)) >>> return rtx_moveable_p (&XEXP (x, 0), OP_IN); >>> return false; >>> >>> ... >>> >>> case CLOBBER: >>> return rtx_moveable_p (&SET_DEST (x), OP_OUT); >>> >>> >>> because that memory clobber is in a parallel statement >>> together with the ASM_OUTPUT. >>> >>> Right? >> >> Yes, that looks correct. And a memory clobber of course _should_ make >> the insn non-moveable as well -- it's an unknown side effect all by >> itself :-) > > Actually, it is not a side effect... Just kind of behaves like it. > But it does *not* prevent the asm from being deleted, for example. > >
Yes, the volatile is still necessary. Bernd.
