On Fri, Apr 20, 2012 at 11:04 AM, Bin.Cheng <amker.ch...@gmail.com> wrote: > On Fri, Apr 20, 2012 at 4:54 PM, Richard Guenther > <richard.guent...@gmail.com> wrote: >> On Fri, Apr 20, 2012 at 9:52 AM, Bin.Cheng <amker.ch...@gmail.com> wrote: >>> On Wed, Apr 18, 2012 at 5:25 PM, Richard Guenther >>> <richard.guent...@gmail.com> wrote: >>>> On Wed, Apr 18, 2012 at 8:53 AM, Bin.Cheng <amker.ch...@gmail.com> wrote: >>> >>>> >>>> I don't understand method 2. I'd do >>>> >>>> start at the single predecessor of the sink-to block >>>> >>>> foreach stmt from the end to the beginning of that block >>>> if the stmt has a VDEF or the same VUSE as the stmt we sink, break >>>> >>>> (continue searching for VDEFs in predecessors - that now gets more >>>> expensive, >>>> I suppose limiting sinking to the cases where the above finds sth >>>> would be easiest, >>>> even limiting sinking to never sink across any stores) >>>> >>>> walk the vuse -> vdef chain, using refs_anti_dependent_p to see whether >>>> the load is clobbered. >>>> >>>> But I'd suggest limiting the sinking to never sink across stores - the >>>> alias >>>> memory model we have in GCC seriously limits these anyway. How would >>>> the numbers change if you do that? >>> Interesting, maybe method 1 I implemented is too conservative. >>> I implemented as you described, and the numbers are: >>> 1) 766, If the stop condition is "stmt_may_clobber_ref_p" >>> 2) 719, if the stop condition is "gimple_vdef || stmt_may_clobber_ref_p" >>> >>> Also, I past make check on x86 for 1). >>> >>> Is it good? I am not sure about it since bootstrapping builds gcc 2 >>> times and libraries 3 times. >> >> For 2) it is enough to test for gimple_vdef. I think that's the most >> reasonable >> approach - we can improve on it once we see that doing so would improve >> things for a testcase. > I am a little confused. > does not "gimple_code (stmt) == GIMPLE_ASM"/"call_may_clobber_ref_p_1 > (stmt, ref)" > matter? These are checked by stmt_may_clobber_ref_p.
All things that clobber anything have gimple_vdef () != NULL. Thus in gimple_vdef () != NULL || stmt_may_clobber_ref_p, stmt_may_clobber_ref_p is never true if gimple_vdef () is NULL. stmt_may_clobber_ref_p isn't checking for a NULL gimple_vdef, but that's because you are not supposed to even have called it then. Richard. > Thanks. > > -- > Best Regards.
