[PATCH PR90078]Capping comp_cost computation in ivopts
Bin.Cheng
amker.cheng@gmail.com
Mon May 6 10:24:00 GMT 2019
On Mon, May 6, 2019 at 6:11 PM Richard Biener
<richard.guenther@gmail.com> wrote:
>
> On Sun, May 5, 2019 at 8:03 AM bin.cheng <bin.cheng@linux.alibaba.com> wrote:
> >
> > > ------------------------------------------------------------------
> > > Sender:Jakub Jelinek <jakub@redhat.com>
> > > Sent At:2019 Apr. 17 (Wed.) 19:27
> > > Recipient:Bin.Cheng <amker.cheng@gmail.com>
> > > Cc:bin.cheng <bin.cheng@linux.alibaba.com>; GCC Patches <gcc-patches@gcc.gnu.org>
> > > Subject:Re: [PATCH PR90078]Capping comp_cost computation in ivopts
> > >
> > >
> > > On Wed, Apr 17, 2019 at 07:14:05PM +0800, Bin.Cheng wrote:
> > > > > As
> > > > > #define INFTY 10000000
> > > > > what is the reason to keep the previous condition as well?
> > > > > I mean, if cost1.cost == INFTY or cost2.cost == INFTY,
> > > > > cost1.cost + cost2.cost >= INFTY too.
> > > > > Unless costs can go negative.
> > > > It's a bit complicated, but in general, costs can go negative.
> > >
> > > Ok, no objections from me then (but as I don't know anything about it,
> > > not an ack either; you are ivopts maintainer, so you don't need one).
> >
> > Hi,
> > The previous patch was reverted on GCC-9 because of PR90240. PR90240 is now
> > fixed by another patch. This is the updated patch for PR90078. It promotes type
> > of ivopts cost from int to int64_t, as well as change behavior of infinite_cost overflow
> > from saturation to assert.
> > Please note, implicit conversions are kept in cost computation as before without
> > introducing any narrowing.
> >
> > Bootstrap/test on x86_64 along with PR90240 patch. Is it OK?
>
> Do not include system headers in .c files, instead those need to be
> (and are already)
> included via system.h.
>
> /* The infinite cost. */
> -#define INFTY 10000000
> +#define INFTY 1000000000L
>
> do we actually need this? What happens on a ilp32 host? That is, I believe
> you can drop the 'L' (it fits into an int anyways)
Yeah, now I think if int64_t is necessary or not. With the scaling
bound and assertions.
>
> @@ -256,6 +259,7 @@ operator- (comp_cost cost1, comp_cost cost2)
> return infinite_cost;
>
> gcc_assert (!cost2.infinite_cost_p ());
> + gcc_assert (cost1.cost - cost2.cost < infinite_cost.cost);
>
> cost1.cost -= cost2.cost;
> cost1.complexity -= cost2.complexity;
>
> probably a pre-existing issue, but we do not seem to handle underflow
> here in general, nor check that underflow doesn't get us below -INFTY.
>
> I guess we really don't want negative costs? That doesn't seem to be
> documented and I was also wondering why the cost isn't unsigned...
>
> @@ -638,7 +646,7 @@ struct iv_ca
> comp_cost cand_use_cost;
>
> /* Total cost of candidates. */
> - unsigned cand_cost;
> + int64_t cand_cost;
>
> /* Number of times each invariant variable is used. */
> unsigned *n_inv_var_uses;
>
> shows this "issue". Can't we use uint64_t throughout the patch?
Oh, it's actually explained in previous message,
https://gcc.gnu.org/ml/gcc-patches/2019-04/msg00697.html
In short, yes the cost can be negative. The negative cost should be
small in absolute value, and we don't check -INFTY. With the scaling
bound change, I don't think -INFTY is possible IIUC.
Thanks,
bin
>
> Otherwise this looks OK.
>
> Thanks,
> Richard.
>
> > Thanks,
> > bin
> > 2019-05-05 Bin Cheng <bin.cheng@linux.alibaba.com>
> >
> > PR tree-optimization/90078
> > * tree-ssa-loop-ivopts.c (inttypes.h): Include new header file.
> > (INFTY): Increase the value for infinite cost.
> > (struct comp_cost): Promote type of members to int64_t.
> > (infinite_cost): Don't set complexity in initialization.
> > (comp_cost::operator +,-,+=,-+,/=,*=): Assert when cost computation
> > overflows to infinite_cost.
> > (adjust_setup_cost): Promote type of parameter and cost computation
> > to int64_t.
> > (struct ainc_cost_data, struct iv_ca): Promote type of member to
> > int64_t.
> > (get_scaled_computation_cost_at, determine_iv_cost): Promote type of
> > cost computation to int64_t.
> > (determine_group_iv_costs, iv_ca_dump, find_optimal_iv_set): Use
> > int64_t's format specifier in dump.
> >
> > 2018-05-05 Bin Cheng <bin.cheng@linux.alibaba.com>
> >
> > PR tree-optimization/90078
> > * g++.dg/tree-ssa/pr90078.C: New test.
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