On Thu, May 26, 2016 at 10:52 AM, Kyrill Tkachov <kyrylo.tkac...@foss.arm.com> wrote: > Hi all, > > On arm we don't have a dedicated instruction that corresponds to a CTZ rtx > but we synthesise it > with an RBIT instruction followed by a CLZ. This is currently done at expand > time. > However, I'd like to push that step until after reload and keep the CTZ rtx > as a single whole in > the early RTL optimisers. This better expresses the semantics of the > operation as a whole, since > the RBIT operation is represented as an UNSPEC anyway and so will not see > the benefits of combine, > and a CTZ-specific optimisation that is implemented in patch 3/3 of this > series won't be triggered > if the expression is broken up into an UNSPEC and a CLZ. > > Therefore this patch changes the expander to expand to a CTZ rtx and split > it after reload into > an RBIT + CLZ to allow sched2 to schedule them apart if it deems necessary. > This patch enables the optimisation in patch 3/3 where the appropriate test > is added. > > Bootstrapped and tested on arm-none-linux-gnueabihf. > > Ok for trunk? > > Thanks, > Kyrill > > 2016-05-26 Kyrylo Tkachov <kyrylo.tkac...@arm.com> > > PR middle-end/37780 > * config/arm/arm.md (ctzsi2): Convert to define_insn_and_split.
OK. Ramana
