[9] RFR(S): 8057622: java/util/stream/test/org/openjdk/tests/java/util/stream/InfiniteStreamWithLimitOpTest: SEGV inside compiled code (sparc)
Vladimir Kozlov
vladimir.kozlov at oracle.com
Wed Nov 5 17:18:13 UTC 2014
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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