String.indexOf optimization

[Martin Buchholz]

If there's a clean improvement in the java code, it's worth putting in.
You can try benchmarking with -Xint.
Are we talking about this method?

    static int indexOf(char[] source, int sourceOffset, int sourceCount,
            char[] target, int targetOffset, int targetCount,
            int fromIndex) {

It does look like we can tighten the code up a little...


On Thu, Jan 8, 2015 at 3:05 PM, Zoltan Sziladi <kissziszi at gmail.com> wrote:

> Thanks for the info.
> So that basically means we have 2 implementations of indexOf currently, one
> is in HotSpot, the other is in the JDK itself, which rarely gets executed.
> Aside from this later fact, isn't it still worth improving the JDK
> implementation if it is possible? I know that the intrinsified method gets
> executed most of the time, but still, if we can improve the JDK
> implementation also, why not? I don't know much about other JVMs but maybe
> a few don't intrinsify it?
>
> Is there any existing test suite which is considered conclusive enough that
> if an implementation beats the naive algorithm in those testcases then it
> could be considered as a replacement in the JDK?
>
> Regards,
> Zoltan
>
>
> On Thu, Jan 8, 2015 at 12:42 PM, Vitaly Davidovich <vitalyd at gmail.com>
> wrote:
>
> > The java impl you saw would be called by (a) interpreter, (b) if you
> > explicitly disable intrinsification of this function, or (c) some other
> JVM
> > that doesn't intrinsify this method (or any method).
> >
> > People don't usually disable intrinsics; if they do, it's because they
> hit
> > some JIT bug and may disable it.
> >
> > On Thu, Jan 8, 2015 at 3:34 PM, Zoltan Sziladi <kissziszi at gmail.com>
> > wrote:
> >
> >> Hi,
> >>
> >> Thanks everyone for all the info.
> >> So, just to go step by step in understanding this.
> >> Andrew said HotSpot would ignore my implementation. So why is there an
> >> implementation of indexOf at all in the JDK, if that's not the code
> that's
> >> executed? Is it just a default fallback? When is the indexOf function
> not
> >> intrinsified? When do people usually disable intrinsification?
> >> Sorry if these are newbie questions, I'm new to this part of Java.
> >>
> >> Regards,
> >> Zoltan
> >>
> >> On Tue, Jan 6, 2015 at 1:28 AM, Andrew Haley <aph at redhat.com> wrote:
> >>
> >> > Hi,
> >> >
> >> > On 05/01/15 18:59, Zoltan Sziladi wrote:
> >> >
> >> > > This discussion was a long time ago, I was just reading through it
> to
> >> > check
> >> > > again what was the last state of the discussion about the
> >> String.indexOf.
> >> > > There is one part which I still do not understand, hopefully someone
> >> > could
> >> > > shed some light on it. A few emails ago Martin mentioned
> >> > >
> >> > > "Hotspot seems to have some intrinsification of String.indexOf,
> which
> >> > > confuses me.
> >> > > Hotspot seems the right place to provide more optimizations for
> this,
> >> > since
> >> > > there has been a fair amount of work creating high-performance
> >> low-level
> >> > > implementations of this idea in C."
> >> > >
> >> > > Then Ivan asked what that actually meant, whether hotspot actually
> >> > replaced
> >> > > the jdk implementation with a low level optimized C implementation,
> >> but I
> >> > > never saw an answer to that.
> >> >
> >> > You can have a look at an implementation of
> >> MacroAssembler::string_indexof
> >> > in
> >> >
> >> >
> >> >
> >>
> http://hg.openjdk.java.net/jdk9/jdk9/hotspot/file/b6b89b8f8531/src/cpu/x86/vm/macroAssembler_x86.cpp
> >> >
> >> > > Can someone please explain this? If we somehow found an algorithm
> that
> >> > beat
> >> > > the naive implementation in the average case, would it be possible
> to
> >> > just
> >> > > implement it in the JDK?
> >> >
> >> > No, because HotSpot would ignore it.  Any speed improvements have to
> be
> >> > done in the architecture-dependent files.
> >> >
> >> > Andrew.
> >> >
> >> >
> >>
> >
> >
>