escape analysis issue with nested objects

[Vitaly Davidovich]

Looking at C2 generated assembly (8u121), both cases are eliminated - the
single() and multi() are dead code.  To alleviate the truly dead code
scenario here, I had these methods return something from the allocated
object (I created a dummy class that holds an int) and accessed those
objects via array indexing - no allocations are generated (not the array,
and not the objects).

On Thu, May 25, 2017 at 3:12 PM, Kirk Pepperdine <kirk.pepperdine at gmail.com>
wrote:

> I can see the arrays being DVE’ed.. in 8_121. EA seems to be doing it’s
> job.
>
> Kind regards,
> Kirk
>
> > On May 25, 2017, at 9:03 PM, Vladimir Kozlov <vladimir.kozlov at oracle.com>
> wrote:
> >
> > Hi Attila,
> >
> > What Java version you are using?
> >
> > I tried jdk 7, 8, 9.
> >
> > What I see is that in both cases only arrays are eliminated (-XX:+PrintEliminateAllocations
> with debug version of VM):
> >
> > BEGIN single
> > Scalar  73    AllocateArray   ===  51  46  47  8  1 ( 71  59  21  58
> 41  1 1 ) [[ 74  75  76  83  84  85 ]]  rawptr:NotNull ( int:>=0,
> java/lang/Object:NotNull *, bool, int ) NewMain::single @ bci:9 !jvms:
> NewMain::single @ bci:9
> > ++++ Eliminated: 73 AllocateArray
> > END single
> > BEGIN multi
> > Scalar  116   AllocateArray   ===  91  86  87  8  1 ( 114  103  21  102
> 41 76  1  1  1 ) [[ 117  118  119  126  127  128 ]]  rawptr:NotNull (
> int:>=0, java/lang/Object:NotNull *, bool, int ) NewMain::multi @ bci:17
> !jvms: NewMain::multi @ bci:17
> > ++++ Eliminated: 116 AllocateArray
> > DONE
> >
> > But based on code non of objects should be allocated - both methods
> should have only 'return' generated.
> >
> > Looks like EA missing such case when objects are stored into small array.
> >
> > Thanks,
> > Vladimir
> >
> > On 5/25/17 9:16 AM, Hontvári Attila wrote:
> >> When creating a non-escaping array and putting a newly created,
> non-escaping object in it, the EA works, there are no heap allocations.
> >>     private static void single() {
> >>         Object x = new Object();
> >>         Object[] array = new Object[]{x};
> >>         Object a = array[0];
> >>     }
> >> But if we do the same with two or more objects, the array will be
> allocated on the heap, and not eliminated.
> >>     private static void multi() {
> >>         Object x = new Object();
> >>         Object y = new Object();
> >>         Object[] array = new Object[]{x, y};
> >>         Object a = array[0];
> >>         Object b = array[1];
> >>     }
> >> Is there a reason why it is only working in the first case?
> >> This would be useful for example, MethodHandle::invokeWithArguments,
> when the primitive types are boxed, and put into a varargs array, see my
> older email [1].
> >> A complete test source code is in [2], if we run it with -verbose:gc,
> we can see there are many GCs in the second case, but there are no GCs in
> the first case.
> >> [1] http://mail.openjdk.java.net/pipermail/jigsaw-dev/2017-
> January/010933.html
> >> [2] https://gist.github.com/anonymous/bd46075ef1ebd858dae49fe6cfe39da8
>
>
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