On Tue, Dec 10, 2013 at 10:44 AM, Richard Sandiford <rdsandif...@googlemail.com> wrote: > "H.J. Lu" <hjl.to...@gmail.com> writes: >> On Tue, Dec 10, 2013 at 10:26 AM, Richard Sandiford >> <rdsandif...@googlemail.com> wrote: >>> "H.J. Lu" <hjl.to...@gmail.com> writes: >>>> On Tue, Dec 10, 2013 at 9:57 AM, Richard Sandiford >>>> <rdsandif...@googlemail.com> wrote: >>>>> "H.J. Lu" <hjl.to...@gmail.com> writes: >>>>>> On Tue, Dec 10, 2013 at 8:05 AM, Kirill Yukhin >>>>>> <kirill.yuk...@gmail.com> wrote: >>>>>>> On 09 Dec 14:08, H.J. Lu wrote: >>>>>>>> >>>>>>>> There are no regressions on Linux/x86-64 with -m32 and -m64. >>>>>>>> Can you check if it improves code quality on x886? >>>>>>> >>>>>>> As second thought. If Tejas and Richard are right and it is simply >>>>>>> incorrect >>>>>>> to check any offsets in this hook, may be we can end up with patch in >>>>>>> the >>>>>>> bottom? >>>>>> >>>>>> What is wrong to pass the correct offset to >>>>>> CANNOT_CHANGE_MODE_CLASS? Backends are free to >>>>>> ignore it. >>>>> >>>>> The point is that: >>>>> >>>>>>> - /* Vector registers do not support subreg with nonzero offsets, >>>>>>> which >>>>>>> - are otherwise valid for integer registers. Since we can't see >>>>>>> - whether we have a nonzero offset from here, prohibit all >>>>>>> - nonparadoxical subregs changing size. */ >>>>>>> - if (GET_MODE_SIZE (to) < GET_MODE_SIZE (from)) >>>>>>> - return true; >>>>> >>>>> seems to be trying to reject things like (subreg:SF (reg:V4SF X) 1), >>>>> which is always invalid for a single-register V4SF. See: >>>> >>>> That is correct. >>> >>> Sorry, what I mean is: that subreg is always invalid for single- >>> register V4SFs regardless of the target. This isn't something that >>> CANNOT_CHANGE_MODE_CLASS should be expected to check. >>> >> >> Why is >> >> (define_insn "*movv4sfdi_subreg" >> [(set (match_operand:DI 0 "nonimmediate_operand" "=rxm") >> (subreg:DI (match_operand:V4SF 1 "register_operand" "x") 0))] >> >> invalid? > > Sorry, I don't understand. I never said it was invalid. I said > (subreg:SF (reg:V4SF X) 1) was invalid if (reg:V4SF X) represents > a single register. On a little-endian target, the offset cannot be > anything other than 0 in that case. > > So the CANNOT_CHANGE_MODE_CLASS code above seems to be checking for > something that is always invalid, regardless of the target. That kind > of situation should be rejected by target-independent code instead. > > In other words I'm arguing against the idea of passing the offset to > CANNOT_CHANGE_MODE_CLASS (which you seemed to be supporting in the > quote above). I think Kirill's patch to remove the i386.c check was > the right way to go. > > There's no need for a separate insn though. Once you allow the subregs > (as per Kirill's patch), the normal move patterns will handle them. >
We will wait for Kirill's results. -- H.J.
