[vector] ClassCastException in C2 with Mask rebracketing

[Adam Pocock]

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

-- 
Adam Pocock
Principal Member of Technical Staff
Machine Learning Research Group
Oracle Labs, Burlington, MA