[9] RFR(S): 8057622: java/util/stream/test/org/openjdk/tests/java/util/stream/InfiniteStreamWithLimitOpTest: SEGV inside compiled code (sparc)
Roland Westrelin
roland.westrelin at oracle.com
Thu Nov 6 10:05:06 UTC 2014
For the record, final webrev looks good to me.
Roland.
> On Nov 6, 2014, at 9:45 AM, Zoltán Majó <zoltan.majo at oracle.com> wrote:
>
> Thank you, Roland, Vladimir, and Albert, for the reviews!
>
>
> Zoltan
>
> On 11/05/2014 06:18 PM, Vladimir Kozlov wrote:
>> This looks good. Don't forget to add label noreg-sqe since we have tests already.
>>
>> Thanks,
>> Vladimir
>>
>> On 11/5/14 5:34 AM, Zoltán Majó wrote:
>>> Hi Vladimir,
>>>
>>>
>>> thank you for the feedback.
>>>
>>> On 11/04/2014 07:40 PM, Vladimir Kozlov wrote:
>>>> On 11/4/14 5:04 AM, Zoltán Majó wrote:
>>>>> Hi Roland, Vladimir, and Albert!
>>>>>
>>>>>
>>>>> thank you for your feedback and for your suggestions! Please see comments on specific issues inline.
>>>>>
>>>>> On 11/04/2014 09:38 AM, Albert Noll wrote:
>>>>>> Hi,
>>>>>>
>>>>>> please see comments inline.
>>>>>> On 11/03/2014 07:00 PM, Vladimir Kozlov wrote:
>>>>>>> I agree with additional check tak != TypeKlassPtr::OBJECT (solution 2).
>>>>>>>
>>>>>>> Instead of creating new LoadKlassNode::make() method you can set control in parseHelper.cpp since it is the only
>>>>>>> place which set it:
>>>>>>>
>>>>>>> Node* a_e_klass = LoadKlassNode::make(_gvn, immutable_memory(), p2, tak);
>>>>>>> if (always_see_exact_class) {
>>>>>>> a_e_klass->init_req(MemNode::Control, control());
>>>>>>> }
>>>>>>> a_e_klass = _gvn.transform(a_e_klass);
>>>>>>>
>>>>>> An alternative solution is to make a default parameter for control. This way we can set the control in make() without
>>>>>> having to add a new make() function.
>>>>>
>>>>> I took Albert's alternative solution. Now we also set the default value for parameter TypeKlassPtr* tk in
>>>>> parseHelper.cpp at line 230.
>>>>
>>>> As I replied to Albert, I think it should be explicit parameter and not default.
>>>> Yes, you would need to modify more files but it is better to be explicit I think.
>>>
>>> OK, I see. I updated the code so that we have one LoadKlassNode::make() method, with the control node as second
>>> parameter. In the new version the control parameter is explicit and we pass in NULL explicitly at all call sites where
>>> control is not needed.
>>>
>>>>
>>>>>
>>>>>>> Also an other reason to have control edge in this place is the address of this klass load is based on ConP constant.
>>>>>>> In a normal case after class check you should have CheckCastPP attached to control and used as address's base.
>>>>>
>>>>> I see, Vladimir. Just a related question: If the address of the klass load were *not* based on a ConP constant, would it
>>>>> be better (or required) to check with a CheckCastPP the value that was loaded?
>>>>
>>>> Yes, you would use CheckCastPP to cast type to exact class you checked for and pin it to 'true' projection of the
>>>> check. As we do for in gen_checkcast() or other places (speculative types).
>>>>
>>>> if (a.class == exact_class)
>>>> (exact_class)a
>>>
>>> Thank you for the explanation.
>>>
>>>>
>>>> In this case you don't need control on following load.
>>>>
>>>>>
>>>>>>>
>>>>>>> And agree with Roland's suggestion about Op_LoadKlass check.
>>>>>>>
>>>>>> What you are suggesting is to make a super class (LoadNode) aware of its subclasses (LoadPNode and LoadKlassNode).
>>>>>> From a software engineering point of view, we should try to avoid doing that. Another solution would be to add a
>>>>>> method (e.g., can_remove_control()) to LoadNode, LoadPNode, and LoadKlassNode. The function returns 'false' for
>>>>>> LoadPNode and LoadKlassNode; and returns 'true' for LoadNode. What do you think?
>>>>>
>>>>> I think Albert's suggestion has the advantage that if we will ever decide to inherit from LoadKlass, we won't have to
>>>>> worry about modifying its superclass. So I think it will be good if we go with it.
>>>>
>>>> I prefer Albert's name can_remove_control()
>>>
>>> OK, I changed the method's name.
>>>
>>> Here is the new webrev: http://cr.openjdk.java.net/~zmajo/8057622/webrev.03/
>>>
>>> All JPRT tests and also the failing test cases pass with the new version.
>>>
>>> Thank you and best regards,
>>>
>>>
>>> Zoltan
>>>
>>>>
>>>> Thanks,
>>>> Vladimir
>>>>
>>>>>
>>>>> Here is the new webrev: http://cr.openjdk.java.net/~zmajo/8057622/webrev.02/
>>>>>
>>>>> JPRT and also the failing test cases pass.
>>>>>
>>>>>
>>>>> Thank you and best regards,
>>>>>
>>>>>
>>>>> Zoltan
>>>>>
>>>>>>
>>>>>> Best,
>>>>>> Albert
>>>>>>
>>>>>>> Thanks,
>>>>>>> Vladimir
>>>>>>>
>>>>>>> On 11/3/14 5:58 AM, Zoltán Majó wrote:
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>>
>>>>>>>> please review the following patch.
>>>>>>>>
>>>>>>>>
>>>>>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8057622
>>>>>>>>
>>>>>>>>
>>>>>>>> Problem:
>>>>>>>>
>>>>>>>>
>>>>>>>> We have five tests that fail with SIGSEGV in our nightlies:
>>>>>>>>
>>>>>>>> java/util/stream/test/org/openjdk/tests/java/util/stream/InfiniteStreamWithLimitOpTest.java
>>>>>>>> java/util/stream/test/org/openjdk/tests/java/util/stream/FlatMapOpTest.java
>>>>>>>> java/util/stream/test/org/openjdk/tests/java/util/stream/StreamSpliteratorTest.java
>>>>>>>> java/util/stream/test/org/openjdk/tests/java/util/stream/StreamBuilderTest.java
>>>>>>>> java/util/stream/test/org/openjdk/tests/java/util/stream/MapOp.java
>>>>>>>>
>>>>>>>> All tests fail when executing the C2-compiled version of
>>>>>>>> java/util/stream/SpinedBuffer at OfPrimitive.inflateSpine():
>>>>>>>>
>>>>>>>>
>>>>>>>> 489: private void inflateSpine() {
>>>>>>>> 490: if (spine == null) {
>>>>>>>> 491: spine = newArrayArray(MIN_SPINE_SIZE);
>>>>>>>> 492: priorElementCount = new long[MIN_SPINE_SIZE];
>>>>>>>> 493: spine[0] = curChunk;
>>>>>>>> 494: }
>>>>>>>> 495: }
>>>>>>>>
>>>>>>>>
>>>>>>>> The failure is due to the 'aastore' at line 493; the failure is caused
>>>>>>>> by the monomorphic array check optimization
>>>>>>>> (-XX:+MonomorphicArrayCheck, enabled by default).
>>>>>>>>
>>>>>>>> In InfiniteStreamWithLimitOpTest.java, C2 determines (based on
>>>>>>>> profiling information) that inflateSpine() has two hot receiver types,
>>>>>>>> SpinedBuffer.OfInt and SpinedBuffer.OfDouble:
>>>>>>>>
>>>>>>>> - in SpinedBuffer.OfInt, the variable 'spine' is of type int[][]
>>>>>>>>
>>>>>>>> - in SpinedBuffer.ofDouble, the variable 'spine' is of type
>>>>>>>> double[][].
>>>>>>>>
>>>>>>>> Please consider the following pseudo Java code that illustrates how C2
>>>>>>>> sees SpinedBuffer.OfPrimitive.inflateSpine() after inlining based on
>>>>>>>> the two hot receiver types SpinedBuffer.OfInt and
>>>>>>>> SpinedBuffer.OfDouble:
>>>>>>>>
>>>>>>>>
>>>>>>>> static void inflateSpine(boolean isOfDouble, Object curChunk) {
>>>>>>>> Object[] spine = isOfDouble ? new double[8][] : new int[8][];
>>>>>>>> spine[0] = curChunk;
>>>>>>>> }
>>>>>>>>
>>>>>>>>
>>>>>>>> If MonomorphicArrayCheck is disabled, C2 checks the element type
>>>>>>>> of 'spine' *at runtime*. The check looks something like:
>>>>>>>>
>>>>>>>>
>>>>>>>> if (!spine.getClass().getComponentType().isInstance(curChunk)) {
>>>>>>>> throw new ArrayStoreException();
>>>>>>>> }
>>>>>>>>
>>>>>>>>
>>>>>>>> If MonomorphicArrayCheck is enabled (our case), C2 creates an array
>>>>>>>> check like this:
>>>>>>>>
>>>>>>>>
>>>>>>>> if (!TYPE.getClass().getComponentType().isInstance(curChunk)) {
>>>>>>>> throw new ArrayStoreException();
>>>>>>>> }
>>>>>>>>
>>>>>>>>
>>>>>>>> where TYPE is the type of the 'spine' variable, as it is determined by
>>>>>>>> C2 *at compile time*. The optimization treats TYPE as a constant and
>>>>>>>> thus saves a load from memory + an offset calculation (I think).
>>>>>>>>
>>>>>>>> The problem is that due to 'spine' being either of type int[][] or of
>>>>>>>> type double[][], C2 determines that TYPE==java/lang/Object.
>>>>>>>>
>>>>>>>> As a result, when the inflateSpine() method is executed, it first loads the
>>>>>>>> Klass* corresponding to java/lang/Object (TYPE). Let us call this Klass*
>>>>>>>> array_klass. Then, the method obtains a Klass* from array_klass->_element_klass.
>>>>>>>> Then, the method reads from offset 20 from array_klass->_element_klass, which
>>>>>>>> results in a SIGSEGV.
>>>>>>>>
>>>>>>>> The reason for the SIGSEGV is that the Klass* array_klass is of type
>>>>>>>> java/lang/Object and is therefore represented as an 'InstanceKlass'.
>>>>>>>> But _element_klass is defined only in objects of type 'ObjArrayKlass'.
>>>>>>>> The compiler reads array_klass->_element_klass because it expects the
>>>>>>>> destination of an 'aastore' to be an array, which is not true if
>>>>>>>> TYPE==java/lang/Object.
>>>>>>>>
>>>>>>>>
>>>>>>>> Solution:
>>>>>>>>
>>>>>>>>
>>>>>>>> The compiler already checks if the compile-time type of the array (TYPE) is
>>>>>>>> the same as the array's type at runtime. If that check fails, the method
>>>>>>>> branches to an uncommon trap. In our case the SIGSEGV happens because
>>>>>>>> the load of array_klass->_element_klass "floats" above the check.
>>>>>>>>
>>>>>>>> I propose two solutions:
>>>>>>>>
>>>>>>>> Solution 1. Add a control edge between the IfTrue branch of the check and
>>>>>>>> the load of _array_klass->_element_klass. That prohibits the load of
>>>>>>>> _array_klass->element_klass floating above the check.
>>>>>>>>
>>>>>>>> Solution 2. In addition to the changes in Solution 1, the compiler checks if
>>>>>>>> the compile-time type of the array (TYPE) is java/lang/Object. If
>>>>>>>> TYPE==java/lang/Object, the compiler should not assume array_type to be
>>>>>>>> TYPE, but should determine array type at runtime instead.
>>>>>>>>
>>>>>>>> The reason is for Solution 2 is: We can't do an array store into a java/lang/Object.
>>>>>>>> So, if we see TYPE==java/lang/Object at compile time, it is pretty sure that the
>>>>>>>> method will deoptimize at runtime. Instead of assuming TYPE to be java/lang/Object,
>>>>>>>> we read at runtime the type of the array store's destination. That still gives us some
>>>>>>>> chance that the compiled version of the method will successfully execute. The
>>>>>>>> additional check is in parseHelper.cpp in Parse::array_store_check() on line 171.
>>>>>>>>
>>>>>>>>
>>>>>>>> Webrev:
>>>>>>>>
>>>>>>>> Solution 1: http://cr.openjdk.java.net/~zmajo/8057622/webrev.00/
>>>>>>>> Solution 2: http://cr.openjdk.java.net/~zmajo/8057622/webrev.01/
>>>>>>>>
>>>>>>>>
>>>>>>>> Testing (for both solutions):
>>>>>>>>
>>>>>>>> JPRT, manual testing with failing test cases.
>>>>>>>>
>>>>>>>>
>>>>>>>> Please note that both solutions are somewhat "hacky", because that allowed me to
>>>>>>>> produce a solution within reasonable time and with reasonable effort. Any suggestions
>>>>>>>> or feedback is welcome.
>>>>>>>>
>>>>>>>>
>>>>>>>> Thank you and best regards,
>>>>>>>>
>>>>>>>>
>>>>>>>> Zoltan
>>>>>>>>
>>>>>>
>>>>>
>>>
>
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