[foreign-memaccess+abi] RFR: Split foreign vector load and store by null or not null base [v2]

[Paul Sandoz]

On Mon, 29 Aug 2022 20:53:43 GMT, Radoslaw Smogura <duke at openjdk.org> wrote:

>> Radoslaw Smogura has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Add unswitching to masked vector operations
>>   Add benchmark covering this.
>>   
>>   After
>>   ```
>>   Benchmark                                          (size)  Mode  Cnt    Score    Error  Units
>>   MemorySegmentMaskedVectorAccess.arrayCopy            1024  avgt   10   16.700 ±  0.612  ns/op
>>   MemorySegmentMaskedVectorAccess.directSegments       1024  avgt   10   80.429 ±  2.897  ns/op
>>   MemorySegmentMaskedVectorAccess.heapSegments         1024  avgt   10   25.528 ±  0.296  ns/op
>>   MemorySegmentMaskedVectorAccess.pollutedSegments2    1024  avgt   10  122.809 ±  0.894  ns/op
>>   MemorySegmentMaskedVectorAccess.pollutedSegments3    1024  avgt   10  252.930 ±  4.623  ns/op
>>   MemorySegmentMaskedVectorAccess.pollutedSegments4    1024  avgt   10  451.579 ±  6.429  ns/op
>>   MemorySegmentMaskedVectorAccess.pollutedSegments5    1024  avgt   10  446.500 ± 39.156  ns/op
>>   ```
>>   
>>   Before
>>   ```
>>   Benchmark                                          (size)  Mode  Cnt    Score     Error  Units
>>   MemorySegmentMaskedVectorAccess.arrayCopy            1024  avgt   10   21.089 ±   0.219  ns/op
>>   MemorySegmentMaskedVectorAccess.directSegments       1024  avgt   10   81.384 ±   1.008  ns/op
>>   MemorySegmentMaskedVectorAccess.heapSegments         1024  avgt   10   25.626 ±   0.522  ns/op
>>   MemorySegmentMaskedVectorAccess.pollutedSegments2    1024  avgt   10  217.733 ±   5.467  ns/op
>>   MemorySegmentMaskedVectorAccess.pollutedSegments3    1024  avgt   10  441.045 ±   9.749  ns/op
>>   MemorySegmentMaskedVectorAccess.pollutedSegments4    1024  avgt   10  522.613 ± 104.997  ns/op
>>   MemorySegmentMaskedVectorAccess.pollutedSegments5    1024  avgt   10  449.814 ±   8.203  ns/op
>>   ```
>
> I think I would need help, as I've found that large number of deoptimizations happens when I execute following code (both in case of Java split and VM split):
> 
>     public static int test3(MemorySegment in, MemorySegment out, MemorySegment out2, byte[] arr) {
>         long sz = in.byteSize();
>         var zero = ByteVector.zero(SPECIES_BYTE);
>         for (long i = 0; i < SPECIES_BYTE.loopBound(in.byteSize()); i += SPECIES_BYTE.vectorByteSize()) {
>             var v1 = ByteVector.fromMemorySegment(SPECIES_BYTE, in, i, ByteOrder.nativeOrder());
> //            arr[i] = (byte) 0;
>             v1.intoMemorySegment(out, i, ByteOrder.nativeOrder());
>         }
> 
>         return 0;
>     }
> 
>     public static void main(String[] args) throws Exception {
>         var session = MemorySession.openConfined();
>         MemorySegment heapIn = MemorySegment.ofArray(new byte[size]);
>         MemorySegment heapOu = MemorySegment.ofArray(new byte[size]);
> 
>         MemorySegment directIn = MemorySegment.allocateNative(size, session);
>         MemorySegment directOu = MemorySegment.allocateNative(size, session);
> 
>         for (int i=0; i < 30_000; i++) {
>             test3(heapIn, heapOu, heapOu, (byte[]) heapOu.array().get());
>             test3(directIn, directOu, directOu, (byte[]) heapOu.array().get());
>         }
>     }
> 
> In compilation log I have huge amount of entries like
> 
> <deoptimized thread='31917' reason='constraint' pc='0x00007fffe134cdc7' compile_id='895' compiler='c1' level='3'>
> <jvms bci='78' method='eu.smogura.panama.tests.vectorscopy.Main test3 (Ljava/lang/foreign/MemorySegment;Ljava/lang/foreign/MemorySegment;Ljava/lang/foreign/MemorySegment;[B)I' bytes='83' count='6061' backedge_count='39955677' iicount='6061' decompiles='95' profile_predicate_traps='100' overflow_recompiles='92'/>
> 
> The VM options I use
> 
> "-XX:+UnlockDiagnosticVMOptions", "-XX:CompileCommand=dontinline,\*::test3\*", "-XX:+LogCompilation",
> 
> 
> Other thing I noticed, there's huge number of _PhaseIdealLoop_ phases (hits allowed maximum) and it create 64 CountedLoopNodes for main part of loop (there's should be at most 4 unswitched branches).
> 
> I wonder if someone could help me with this concern?

@rsmogura you need some guidance from HotSpot engineers such as @iwanowww

-------------

PR: https://git.openjdk.org/panama-foreign/pull/711