box and val (c2 crash)

Remi Forax forax at univ-mlv.fr
Mon Jan 28 15:01:07 UTC 2019


I believe those patchs (or maybe one before) has introduced a regression

This code doesn't compile anymore:
public class Regression {
  static value class Entry<E> {
    private final int value;

    public Entry(int value) {
      this.value = value;
    }
    
    public static <E> Entry<E>[] of() {
      return (Entry<E>[])new Entry<?>[0]; 
    }
  }
  
  public static void main(String[] args) {
    var entry = Entry.of();
  }
}

./src/main/java/fr.umlv.valuetype/fr/umlv/valuetype/Regression.java:12: error: incompatible types: Entry<?>[] cannot be converted to Entry<E>[]
      return (Entry<E>[])new Entry<?>[0]; 
                         ^
  where E is a type-variable:
    E extends Object declared in method <E>of()

Rémi

----- Mail original -----
> De: "Srikanth" <srikanth.adayapalam at oracle.com>
> À: "valhalla-dev" <valhalla-dev at openjdk.java.net>
> Envoyé: Lundi 28 Janvier 2019 13:03:29
> Objet: Re: box and val (c2 crash)

> On 07/01/19 3:07 PM, Srikanth wrote:
>> Hi Remi,
>>
>> For the observation about javac, I will take a look and follow up.
> 
> Hi Remi,
> 
> The two issues reported in this mail are fixed via:
> 
> https://bugs.openjdk.java.net/browse/JDK-8217875 and
> https://bugs.openjdk.java.net/browse/JDK-8217872
> 
> Let me know if you continue to see any problems with these constructs.
> 
> Thanks!
> Srikanth
> 
>>
>> Thanks!
>> Srikanth
>>
>> On 03/01/19 8:44 PM, Remi Forax wrote:
>>> Now, i've tried to play with the .box/.val trying to implement the
>>> clojure Cursor protocol,
>>> which iterate like it's an abstract linked list, so at each step
>>> either you return a new Cursor (a value type) or null at the end
>>> (which seems to be a good test for a nullable value type).
>>>
>>> The following code compiles !
>>> I had to had the fix method because the compier refuse to find any
>>> methods on Cursor.box and
>>>    Cursor.box boxed = ...
>>>    ((Cursor)boxed).next
>>> doesn't compile too.
>>>
>>> If you try to execute the code, it crashes the VM (in the C2 compiler
>>> thread it seems)
>>>
>>> Current CompileTask:
>>> C2:    338  119 fr.umlv.valuetype.perf.TupleLoopBenchMark::sum (46
>>> bytes)
>>>
>>> Stack: [0x00007ff4c0a37000,0x00007ff4c0b38000],
>>> sp=0x00007ff4c0b34700,  free space=1013k
>>> Native frames: (J=compiled Java code, A=aot compiled Java code,
>>> j=interpreted, Vv=VM code, C=native code)
>>> V  [libjvm.so+0xe19ed6]  VMError::report_and_die(int, char const*,
>>> char const*, __va_list_tag*, Thread*, unsigned char*, void*, void*,
>>> char const*, int, unsigned long)+0x186
>>> V  [libjvm.so+0xe1ac87]  VMError::report_and_die(Thread*, void*, char
>>> const*, int, char const*, char const*, __va_list_tag*)+0x47
>>> V  [libjvm.so+0x67a68e]  report_vm_error(char const*, int, char
>>> const*, char const*, ...) [clone .constprop.51]+0xee
>>> V  [libjvm.so+0xdbc39e]  TypePtr::xmeet_helper(Type const*) const+0x5e
>>> V  [libjvm.so+0xdb80e0]  TypePtr::xmeet(Type const*) const+0x10
>>> V  [libjvm.so+0x5564c1]  PhiNode::Value(PhaseGVN*) const+0x131
>>> V  [libjvm.so+0xc38986] PhaseGVN::transform_no_reclaim(Node*)+0x86
>>> V  [libjvm.so+0xc00c2d]  Parse::do_exits()+0x4bd
>>> V  [libjvm.so+0xc05c16]  Parse::Parse(JVMState*, ciMethod*, float)+0xab6
>>> V  [libjvm.so+0x53da48] ParseGenerator::generate(JVMState*)+0x88
>>> V  [libjvm.so+0x70f87d]  Parse::do_call()+0x2dd
>>> V  [libjvm.so+0xc15998]  Parse::do_one_bytecode()+0x32e8
>>> V  [libjvm.so+0xc03077]  Parse::do_one_block()+0x197
>>> V  [libjvm.so+0xc034e2]  Parse::do_all_blocks()+0x102
>>> V  [libjvm.so+0xc05bd0]  Parse::Parse(JVMState*, ciMethod*, float)+0xa70
>>> V  [libjvm.so+0x53da48] ParseGenerator::generate(JVMState*)+0x88
>>> V  [libjvm.so+0x61bab8]  Compile::Compile(ciEnv*, C2Compiler*,
>>> ciMethod*, int, bool, bool, bool, DirectiveSet*)+0xe98
>>> V  [libjvm.so+0x53cf46]  C2Compiler::compile_method(ciEnv*,
>>> ciMethod*, int, DirectiveSet*)+0xe6
>>> V  [libjvm.so+0x624182]
>>> CompileBroker::invoke_compiler_on_method(CompileTask*)+0x3a2
>>> V  [libjvm.so+0x6255c8] CompileBroker::compiler_thread_loop()+0x608
>>> V  [libjvm.so+0xda42f8]  JavaThread::thread_main_inner()+0xf8
>>> V  [libjvm.so+0xda0fc1]  Thread::call_run()+0x171
>>> V  [libjvm.so+0xbd5598]  thread_native_entry(Thread*)+0xf8
>>>
>>>
>>> Rémi
>>>
>>> ---
>>>    static value class Tuple {
>>>      private final int index;
>>>      private final int element;
>>>                private Tuple(int index, int element) {
>>>        this.index = index;
>>>        this.element = element;
>>>      }
>>>    }
>>>       static value class Cursor {
>>>      private final int[] array;
>>>      private final int index;
>>>           private Cursor(int[] array, int index) {
>>>        this.array = array;
>>>        this.index = index;
>>>      }
>>>           Tuple current() {
>>>        return new Tuple(index, array[index]);
>>>      }
>>>           Cursor.box next() {
>>>        if (index + 1 == array.length) {
>>>          return null;
>>>        }
>>>        return new Cursor(array, index + 1);
>>>      }
>>>    }
>>>       private static Cursor.box indexedElements(int[] array) {
>>>      if (array.length == 0) {
>>>        return null;
>>>      }
>>>      return new Cursor(array, 0);
>>>    }
>>>       private static Cursor fix(Cursor.box cursor) {
>>>      return cursor;
>>>    }
>>>       @Benchmark
>>>    public int sum() {
>>>      int sum = 0;
>>>      for(Cursor.box cursor = indexedElements(ARRAY); cursor != null;
>>> cursor = fix(cursor).next()) {
>>>        Tuple tuple = fix(cursor).current();
>>>        sum += tuple.index + tuple.element;
>>>      }
>>>      return sum;
>>>    }
>>>


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