[x265] [PATCH 2 of 3] improve duplicate MV check by reduce condition jump

[Deepthi Nandakumar]

Ok, cool. The short circuiting is mandated by the C++ specification, so
it's not really compiler dependent.

On Mon, Jun 29, 2015 at 10:17 PM, chen <chenm003 at 163.com> wrote:

> Most compiler will do a good optimize on it, the && must generate jump
> since maybe side effect on previous operator.
>
> this condition and above mvc[i].clipped(qmvmin, qmvmax) is highest
> component in MotionEstimate::motionEstimate
>
> At 2015-06-30 00:42:48,"Deepthi Nandakumar" <deepthi at multicorewareinc.com>
> wrote:
>
> Hmm, but arent the benefits very compiler dependent? Since this isnt the
> innermost loop, is the readability loss worth it?
> On Jun 29, 2015 9:27 PM, "Steve Borho" <steve at borho.org> wrote:
>
>> It is avoiding the C short-circuit logic that is necessary for &&. With
>> & the compiler does not have to perform early-out jumps for each
>> condition. Instead it does all the & operations then does a single
>> conditional jump.
>>
>> It can often be faster, but you have to take a lot of care that the
>> & does the right thing.
>>
>> On 06/29, Deepthi Nandakumar wrote:
>> > Hi,
>> >
>> > How does this improve the generated asm code/cycles taken?
>> >
>> > On Sat, Jun 27, 2015 at 7:43 AM, Min Chen <chenm003 at 163.com> wrote:
>> >
>> > > # HG changeset patch
>> > > # User Min Chen <chenm003 at 163.com>
>> > > # Date 1435370055 25200
>> > > # Node ID a8198965fbf18d7ced2cd8e8acd07fcc4ee6a2b3
>> > > # Parent  229602ba850eb11c171d8c3cbb049dda4b41abda
>> > > improve duplicate MV check by reduce condition jump
>> > > ---
>> > >  source/encoder/motion.cpp |    4 ++--
>> > >  1 files changed, 2 insertions(+), 2 deletions(-)
>> > >
>> > > diff -r 229602ba850e -r a8198965fbf1 source/encoder/motion.cpp
>> > > --- a/source/encoder/motion.cpp Fri Jun 26 18:54:13 2015 -0700
>> > > +++ b/source/encoder/motion.cpp Fri Jun 26 18:54:15 2015 -0700
>> > > @@ -645,7 +645,7 @@
>> > >          for (int i = 0; i < numCandidates; i++)
>> > >          {
>> > >              MV m = mvc[i].clipped(qmvmin, qmvmax);
>> > > -            if (m.notZero() && m != pmv && m != bestpre) // check
>> already
>> > > measured
>> > > +            if (m.notZero() & (m != pmv ? 1 : 0) & (m != bestpre ? 1
>> :
>> > > 0)) // check already measured
>> > >              {
>> > >                  int cost = ref->lowresQPelCost(fenc, blockOffset, m,
>> sad)
>> > > + mvcost(m);
>> > >                  if (cost < bprecost)
>> > > @@ -661,7 +661,7 @@
>> > >          for (int i = 0; i < numCandidates; i++)
>> > >          {
>> > >              MV m = mvc[i].clipped(qmvmin, qmvmax);
>> > > -            if (m.notZero() && m != pmv && m != bestpre) // check
>> already
>> > > measured
>> > > +            if (m.notZero() & (m != pmv ? 1 : 0) & (m != bestpre ? 1
>> :
>> > > 0)) // check already measured
>> > >              {
>> > >                  int cost = subpelCompare(ref, m, sad) + mvcost(m);
>> > >                  if (cost < bprecost)
>> > >
>> > > _______________________________________________
>> > > x265-devel mailing list
>> > > x265-devel at videolan.org
>> > > https://mailman.videolan.org/listinfo/x265-devel
>> > >
>>
>> > _______________________________________________
>> > x265-devel mailing list
>> > x265-devel at videolan.org
>> > https://mailman.videolan.org/listinfo/x265-devel
>>
>>
>> --
>> Steve Borho
>> _______________________________________________
>> x265-devel mailing list
>> x265-devel at videolan.org
>> https://mailman.videolan.org/listinfo/x265-devel
>>
>
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>
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