2012/3/30 Jan Hubicka <hubi...@ucw.cz>: >> On Thu, Mar 29, 2012 at 8:34 PM, Richard Henderson <r...@redhat.com> wrote: >> > On 03/29/2012 01:16 PM, Jan Hubicka wrote: >> >>> Of course, there's still the problem of getting the unwind data correct >> >>> at >> >>> the point of the asm. I commented about that in the PR you filed. >> >> >> >> I think i386 still has the problem that it is small register class target >> >> and if you >> >> set rdi/rax and friends as hard registers, you risk reload failures. >> > >> > True, and if this were i386 code I would certainly recommend using the >> > [acd] >> > constraints instead (for suitible regparm signature). But this is >> > explicitly >> > x86_64 code and the compiler has 8 registers otherwise available. > > Sure, still rdi/rax is the only option for some of instructions, so x86-64 > doesn't really solve all the problems. >> > >> >> Do we prevent code motion of hard registers sets i.e. at GIMPLE level? >> >> Yes we do (modulo bugs). > > Good. Note that this also include transformations like frward substitution > into > area where hard register is live (i.e. it is not enough to just not touch hard > registers as volatile, but one needs to prevent moving other code in).
Motion across hardreg sets/uses are not restricted. And I would not expect an optimizing compiler to do that (it's your own fault to use hardregs in complex C code). Richard.
