[PATCH] Add loop unrolling metadata descriptions to LangRef.rst

[Mark Heffernan]

On Fri, Jul 18, 2014 at 12:01 PM, Hal Finkel <hfinkel at anl.gov> wrote:

> Yes, I think so.
>

Thanks.  Committed as  r213397.

Mark


>  -Hal
>
> ----- Original Message -----
> > From: "Mark Heffernan" <meheff at google.com>
> > To: "Mark Heffernan" <meheff at google.com>, "Hal Finkel" <hfinkel at anl.gov>
> > Cc: llvm-commits at cs.uiuc.edu
> > Sent: Friday, July 18, 2014 1:08:56 PM
> > Subject: Re: [PATCH] Add loop unrolling metadata descriptions to
> LangRef.rst
> >
> >
> > Is this patch good to go? The changes we talked about (renaming
> > metadata) will be in follow up patches.
> >
> >
> > Mark
> >
> >
> >
> > On Fri, Jul 18, 2014 at 10:28 AM, Mark Heffernan < meheff at google.com
> > > wrote:
> >
> >
> >
> > ================
> > Comment at: docs/LangRef.rst:2965
> > @@ +2964,3 @@
> > +bit operand value is 0 loop unrolling is disabled. A value of 1
> > +indicates that the loop should be fully unrolled. For example:
> > +
> > ----------------
> >
> > Mark Heffernan wrote:
> > > hfinkel at anl.gov wrote:
> > > > I find this confusing. Specifically, to get partial unrolling,
> > > > what needs to happen? If I want partial unrolling with a
> > > > specific count, do I need both the 'count' and 'enable'
> > > > metadata?
> > > I added a bit more explanation about that case.
> > >
> > > I'd imagine an underlying cause of confusion is that
> > > ``llvm.loop.unroll.enable 1`` doesn't exactly mean enable. It
> > > means try to fully unroll the loop. So we want the following
> > > possible hints:
> > >
> > > don't unroll
> > > unroll fully
> > > unroll by N
> > >
> > > This doesn't exactly map nicely to the two metadata we have (one
> > > with boolean operand, one with i32). Maybe a cleaner way to have
> > > done this is with the following metadata:
> > >
> > > llvm.loop.unroll.disable (no operand)
> > > llvm.loop.unroll.fully_unroll (no operand)
> > > llvm.loop.unroll.count i32
> > >
> > > And only allow a single loop unroll metadata node per loop. Worth
> > > making this change?
> > I should add that this confusion is also baked into the pragma
> > syntax. The following means unroll fully:
> >
> > #pragma clang loop unroll(enable)
> >
> > http://reviews.llvm.org/D4576
> >
> >
> >
> >
>
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
>
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