escape analysis issue with nested objects

[Kirk Pepperdine]

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