box and val (c2 crash)

Tobias Hartmann tobias.hartmann at oracle.com
Mon Jan 7 09:55:51 UTC 2019


Hi Remi,

I fixed the issue with JDK-8216260:
http://hg.openjdk.java.net/valhalla/valhalla/rev/09d9f9085910

The problem was that we tried to scalarize a boxed value type return which obviously fails if null
is returned. Could you please verify that the fix solves the crashes you were seeing?

Thanks,
Tobias

On 04.01.19 15:25, Tobias Hartmann wrote:
> Hi Remi,
> 
> thanks a lot for reporting these issues. I'll have a look!
> 
> Best regards,
> Tobias
> 
> 
> On 04.01.19 15:14, Remi Forax wrote:
>> I believe the crash comes from the method "next()" (or indexedElements() because it the same kind of code),
>>
>>   Cursor.box next() {
>>     if (index + 1 == array.length) {
>>       return null;
>>     }
>>     return new Cursor(array, index + 1);
>>   }
>>
>> There is a merge of either null or a Cursor (which is a value type) into a register typed Cursor.box.
>>
>> Trying to insert a local variable in between result in a crash in a different methods
>>   Cursor.box next() {
>>     Cursor.box box;
>>     if (index + 1 == array.length) {
>>       box = null;
>>     } else {
>>       box = new Cursor(array, index + 1);
>>     }
>>     return box;
>>   }
>>
>> Current CompileTask:
>> C2:    308  117             fr.umlv.valuetype.perf.TupleLoopBenchMark$Cursor::next (38 bytes)
>>
>> Stack: [0x00007fb3b253c000,0x00007fb3b263d000],  sp=0x00007fb3b2639d00,  free space=1015k
>> Native frames: (J=compiled Java code, A=aot compiled Java code, j=interpreted, Vv=VM code, C=native code)
>> V  [libjvm.so+0xde246f]  ValueTypeNode::make_from_oop(GraphKit*, Node*, ciValueKlass*)+0x9f
>> V  [libjvm.so+0xc06567]  Parse::return_current(Node*)+0x8d7
>> V  [libjvm.so+0xc14dc4]  Parse::do_one_bytecode()+0x2714
>> 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
>>
>> ----- Mail original -----
>>> De: "Remi Forax" <forax at univ-mlv.fr>
>>> À: "valhalla-dev" <valhalla-dev at openjdk.java.net>
>>> Envoyé: Jeudi 3 Janvier 2019 16:14:22
>>> Objet: box and val (c2 crash)
>>
>>> 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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