[vector] ClassCastException in C2 with Mask rebracketing
Vladimir Ivanov
vladimir.x.ivanov at oracle.com
Fri Feb 23 12:17:33 UTC 2018
Adam,
Please, try the following patch (on top of the one Razvan sent out
yesterday [1]):
http://cr.openjdk.java.net/~vlivanov/panama/vector.generalized_intrinsics/webrev.07
It fixes CCE bug for me.
Regarding generated code quality, I see issues with vector box
elimination and they are caused by:
(1) no intrinsic for Mask.not() yet [2]
(2) interface calls hinders the analysis by wrappign VectorBox nodes
into CheckCastPP which hide exact class info by casting them to interfaces
Best regards,
Vladimir Ivanov
[1]
http://cr.openjdk.java.net/~rlupusoru/panama/webrev_maskboxingavx512_02/index.html
[2] @ 259 jdk.incubator.vector.AbstractMask::not (5 bytes) inline (hot)
\-> TypeProfile (721/721 counts) =
jdk/incubator/vector/Float256Vector$Float256Mask
@ 1 jdk.incubator.vector.AbstractMask::not (10 bytes) inline
(hot)
@ 1
java.lang.invoke.LambdaForm$MH/100555887::linkToTargetMethod (8 bytes)
force inline by annotation
@ 4 java.lang.invoke.LambdaForm$MH/611437735::invoke (8
bytes) force inline by annotation
@ 6 jdk.incubator.vector.Float256Vector$Float256Mask::uOp (6
bytes) inline (hot)
@ 2 jdk.incubator.vector.Float256Vector$Float256Mask::uOp
(61 bytes) too big
[3]
On 2/21/18 11:59 PM, Adam Pocock wrote:
> Ok. I'm trying to work around this issue by turning off C2 compilation
> of the binarySearchCDF method, so I can do correctness testing on the
> rest of the SIMD code, and maybe put it in a profiler to see how many
> cache misses I'm causing etc.
>
> I'm using "-XX:CompilerDirectivesFile=filename" pointed at a directives
> file containing:
>
> [
> {
> match:
> "com/oracle/labs/mlrg/topicmodel/util/vector/BinarySearch.binarySearchCDF*",
>
> c2: {
> Exclude: true,
> },
> },
> {
> match: "*Float256Vector$Float256Mask.rebracket*",
> c2: {
> Exclude: true,
> },
> },
> {
> match: "*Int256Vector$Int256Mask.rebracket*",
> c2: {
> Exclude: true,
> },
> },
> ]
>
> but all I've managed to do is move around the place where I get a
> ClassCastException. It's still in the binarySearch but it moves to
> different rebracket operations. I did once manage to move it to a
> completely incomprehensible place where it dies with ClassCastException
> from Float256Vector to Int256Vector, in a function which only takes
> IntVector arguments, but that was after the binary search call and I
> suspect something weird is happening.
>
> Also now when I turn off the vector intrinsics with
> "-XX:-UseVectorApiIntrinsics" and remove the compiler directives,
> Hotspot core dumps midway through execution. It runs past that point if
> I turn off C2 with "-XX:TieredStopAtLevel=3".
>
> Feb 21, 2018 3:53:08 PM com.oracle.labs.mlrg.topicmodel.model.train.SSCA
> train
> INFO: Iteration 0
> #
> # A fatal error has been detected by the Java Runtime Environment:
> #
> # Internal Error (compile.cpp:2695), pid=21949, tid=21976
> # Error: fatal error
> #
> # JRE version: OpenJDK Runtime Environment (11.0) (build
> 11-internal+0-adhoc.apocock.panama)
> # Java VM: OpenJDK 64-Bit Server VM (11-internal+0-adhoc.apocock.panama,
> mixed mode, tiered, compressed oops, g1 gc, linux-amd64)
> # Core dump will be written. Default location: Core dumps may be
> processed with "/usr/share/apport/apport %p %s %c %d %P" (or dumping to
> /local/Repositories/TopicModel/reuters-test/core.21949)
>
> Should I just wait till the generalised intrinsics support has fully
> landed? Is there some Hotspot incantation which will let me test out
> areas of the code which don't use casting.
>
> Thanks,
>
> Adam
>
> On 16/02/18 18:14, Vladimir Ivanov wrote:
>>
>>> Yep, the problem went away with "-XX:-UseVectorApiIntrinsics". My
>>> vector shapes are unchanging though, everything is fixed at S256Bit
>>> as that's what I've got on my desktop. I thought the rebracket for
>>> things like masks were supposed to be optimised out, as a Float 256
>>> Mask is the same bit string as an Integer 256 Mask.
>>
>> Yes, rebracketing turns into an no-op when boxes go away. Otherwise,
>> the operand has to be boxed/reboxed.
>>
>>> Any idea when the generalized intrinsics will land?
>>
>> The first batch is already there, but no exact dates when the rest
>> follow.
>>
>> Best regards,
>> Vladimir Ivanov
>>
>>> On 15/02/18 12:50, Vladimir Ivanov wrote:
>>>> Adam,
>>>>
>>>> Thanks for the report.
>>>>
>>>> I hit a similar problem with vectors and tracked it down to a
>>>> changes in Parse::do_call (disabled C->optimize_virtual_call() on
>>>> vectors). The bug is devirtualized non-inlined call can float before
>>>> the type check it depends on. It leads to a wrong method being
>>>> called when type check fails and manifests as a CCE in interpreter
>>>> after deoptimization (due to failed type check). It usually happens
>>>> when vector shapes change at runtime: C2 produces a method
>>>> specialized for some particular vector shape and then the first time
>>>> the method observes a different vector shape.
>>>>
>>>> The problem is specific to original intrinsics which rely on some
>>>> inlining tweaks (like in Parse::do_call) to make intrinsification
>>>> more reliable.
>>>>
>>>> I suggest you to try -XX:-UseVectorApiIntrinsics and check whether
>>>> the problem goes away.
>>>>
>>>> Generalized intrinsics will be used (where available) and they
>>>> shouldn't be prone to that problem (relevant code path in
>>>> Parse::do_call is used only for original intrinsics).
>>>>
>>>> Unfortunately, not all operations are covered by generalized
>>>> intrinsics yet. So, generated code quality may suffer as well.
>>>>
>>>> I didn't bother fixing the bug because the plan is to replace
>>>> original intrinsics with generalized ones and remove inlining tweaks.
>>>>
>>>> Best regards,
>>>> Vladimir Ivanov
>>>>
>>>> On 2/15/18 8:11 PM, Adam Pocock wrote:
>>>>> Hi,
>>>>>
>>>>> I've been working on more involved machine learning demos on top of
>>>>> the vector API. As part of that I built a binary search demo that
>>>>> searches n vectors at the same time using an n-wide SIMD. This
>>>>> keeps rebracketing the Mask from Integer to Float and back again as
>>>>> it searches through the arrays.
>>>>>
>>>>> Paul Sandoz has been helping me debug it, and when this code is run
>>>>> using C1 or lower it executes fine, but when it's recompiled with
>>>>> C2 (triggered by executing binarySearchCDF in a loop with the same
>>>>> arguments and a print statement, takes about 300-500 iterations) it
>>>>> throws a ClassCastException (stack trace below). Turning off C2
>>>>> with "-XX:TieredStopAtLevel=3" allows the loop to complete.
>>>>>
>>>>> Code:
>>>>>
>>>>> public static <S extends Vector.Shape> IntVector<S>
>>>>> binarySearchCDF(IntSpecies<S> spec, float[][] input, int fromIndex,
>>>>> int toIndex, FloatVector<S> key) {
>>>>> IntVector<S> low = spec.broadcast(fromIndex);
>>>>> IntVector<S> high = spec.broadcast(toIndex - 1);
>>>>> IntVector<S> one = spec.broadcast(1);
>>>>>
>>>>> Mask<Float,S> mask = key.species().trueMask();
>>>>>
>>>>> int[] indicesBuffer = new int[key.length()];
>>>>> float[] valuesBuffer = new float[key.length()];
>>>>>
>>>>> while (mask.anyTrue()) {
>>>>> IntVector<S> mid =
>>>>> low.add(high,mask.rebracket(Integer.class)).shiftR(1);
>>>>> mid.intoArray(indicesBuffer,0);
>>>>> for (int i = 0; i < valuesBuffer.length; i++) {
>>>>> valuesBuffer[i] = input[i][indicesBuffer[i]];
>>>>> }
>>>>> FloatVector<S> values =
>>>>> key.species().fromArray(valuesBuffer,0);
>>>>>
>>>>> Mask<Integer,S> lessThanKey =
>>>>> values.lessThan(key).and(mask).rebracket(Integer.class);
>>>>> low = low.blend(mid.add(one),lessThanKey);
>>>>> Mask<Integer,S> greaterThanKey =
>>>>> values.greaterThan(key).and(mask).rebracket(Integer.class);
>>>>> high = high.blend(mid.sub(one),greaterThanKey);
>>>>> Mask<Integer,S> equalsKey =
>>>>> values.equal(key).and(mask).rebracket(Integer.class);
>>>>> low = low.blend(mid,equalsKey);
>>>>> mask = mask.and(equalsKey.rebracket(Float.class).not());
>>>>> mask =
>>>>> mask.and(low.lessThan(high).rebracket(Float.class));
>>>>> }
>>>>>
>>>>> return low;
>>>>> }
>>>>>
>>>>> Stack trace:
>>>>>
>>>>> Caused by: java.lang.ClassCastException:
>>>>> jdk.incubator.vector/jdk.incubator.vector.Int256Vector$Int256Mask
>>>>> cannot be cast to
>>>>> jdk.incubator.vector/jdk.incubator.vector.Float256Vector$Float256Mask
>>>>> at
>>>>> jdk.incubator.vector/jdk.incubator.vector.Float256Vector$Float256Mask.and(Float256Vector.java:488)
>>>>>
>>>>> at
>>>>> jdk.incubator.vector/jdk.incubator.vector.Float256Vector$Float256Mask.and(Float256Vector.java:430)
>>>>>
>>>>> at
>>>>> mlrg.topicmodel/com.oracle.labs.mlrg.topicmodel.util.vector.BinarySearch.binarySearchCDF(BinarySearch.java:37)
>>>>>
>>>>>
>>>>> Line 37 is:
>>>>> mask = mask.and(equalsKey.rebracket(Float.class).not());
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Adam
>>>>>
>>>
>
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