On 12/16/2015 03:30 PM, Evandro Menezes wrote: > > On 10/30/2015 05:24 AM, Marcus Shawcroft wrote: > > On 20 October 2015 at 00:40, Evandro Menezes <e.mene...@samsung.com> >wrote: > > In the existing targets, it seems that it's always faster to zero >up a DF > > register with "movi %d0, #0" instead of "fmov %d0, xzr". > > This patch modifies the respective pattern. > > > Hi Evandro, > > This patch changes the generic, u architecture independent instruction > selection. The ARM ARM (C3.5.3) makes a specific recommendation about > the choice of instruction in this situation and the current > implementation in GCC follows that recommendation. Wilco has also > picked up on this issue he has the same patch internal to ARM along > with an ongoing discussion with ARM architecture folk regarding this > recommendation. I'm reluctant to take this patch right now on the > basis that it runs contrary to ARM ARM recommendation pending the > conclusion of Wilco's discussion with ARM architecture folk. > > > Have you had a chance to discuss this internally further?
Yes, it was decided to remove the recommendation from future ARM ARM's. Several review comments on your patch (https://patchwork.ozlabs.org/patch/532736): * This should be added to movhf, movsf and movdf - movtf already does this. * It is important to set the "fp" and "simd" attributes so that the movi variant can only be selected if it is available. Cheers, Wilco
