RFR: 8287292: Improve TransformKey to pack more kinds of transforms efficiently [v3]

[Mandy Chung]

On Wed, 25 May 2022 14:13:52 GMT, Claes Redestad <redestad at 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
>
> Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Missed correctly taking b1 into account in of(byte, int, int...) (java/lang/String/concat/ImplicitStringConcatShapes.java test failure)

LGTM with a couple of suggestions.

src/java.base/share/classes/java/lang/invoke/LambdaFormEditor.java line 219:

> 217:             return new TransformKey(fullBytes);
> 218:         }
> 219:         static TransformKey of(byte kind, int b1, int b2, int[] b3456) {

Nit: I can't figure out if `b3456` intends to be a different convention than the others `b123` and `b234`.  I would expect something like this:

Suggestion:

        static TransformKey of(byte kind, int b1, int b2, int... b345) {

src/java.base/share/classes/java/lang/invoke/LambdaFormEditor.java line 252:

> 250:             if (!inRange(bitset))
> 251:                 return 0;
> 252:             pb = pb | b2 << (2 * PACKED_BYTE_SIZE) | b1 << PACKED_BYTE_SIZE | b0;

Suggestion:

            pb = pb | packagedBytes(b0, b1, b2);

src/java.base/share/classes/java/lang/invoke/LambdaFormEditor.java line 267:

> 265:             if (!inRange(bitset))
> 266:                 return 0;
> 267:             pb = pb | b1 << PACKED_BYTE_SIZE | b0;

Suggestion:

            pb = pb | packagedBytes(b0, b1);

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

Marked as reviewed by mchung (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/8881