On Wed, 25 May 2022 13:27:17 GMT, Jorn Vernee <jver...@openjdk.org> wrote:
>> The bespoke caching scheme in `jl.invoke.LambdaFormEditor.TransformKey`
>> allows keys to be compacted when all byte values of the key fit in 4 bits,
>> otherwise a byte array is allocated and used. This means that all transforms
>> with a kind value above 15 will be forced to allocate and use array
>> comparisons.
>>
>> Removing unused and folding some transforms to ensure all existing kinds can
>> fit snugly within the 0-15 value range realize a minor improvement to
>> footprint, speed and allocation pressure of affected transforms, e.g.
>> ~300bytes/op reduction in the `StringConcatFactoryBootstraps` microbenchmark:
>>
>> Baseline:
>>
>> Benchmark Mode Cnt
>> Score Error Units
>> SCFB.makeConcatWithConstants avgt 15
>> 2048.475 ? 69.887 ns/op
>> SCFB.makeConcatWithConstants:?gc.alloc.rate.norm avgt 15
>> 3487.311 ? 80.385 B/op
>>
>>
>> Patched:
>>
>> Benchmark Mode Cnt
>> Score Error Units
>> SCFB.makeConcatWithConstants avgt 15
>> 1961.985 ? 101.519 ns/op
>> SCFB.makeConcatWithConstants:?gc.alloc.rate.norm avgt 15
>> 3156.478 ? 183.600 B/op
>
> src/java.base/share/classes/java/lang/invoke/LambdaFormEditor.java line 239:
>
>> 237: for (int i = 0; i < b23456.length; i++) {
>> 238: int b = b23456[i] & 0xFF;
>> 239: bitset |= b;
>
> Looks like `b` is always truncated. I wonder what happens if the ints in this
> array are larger than a byte (which seems to be possible in e.g. the case of
> argument positions). Some higher order bits might be dropped, but the
> resulting `b` might only have the least significant 4 bits set.
>
> I think the untruncated value should be used to compute the bitset? `butset
> |= b23456[i]`? Then the `inRange` check should reject that case.
Maybe not... argument positions should fit in a byte as well. But, maybe there
are other problematic cases? Or are the ints guaranteed to fit in a byte?
-------------
PR: https://git.openjdk.java.net/jdk/pull/8881
