RFR: 8246152: Improve String concat bootstrapping

[Remi Forax]

Hi Claes,
For the code below the comment "Mock the recipe to reuse the concat generator code",
i believe you can use String.repeat() that was introduced recently.

The code that parse the the receipe can be in its own method to make the code more readable,
this method returns the list and use the StringBuilder internally.

In generateMHInlineCopy,
  element.get(0) and element.get(1) should be stored in local variables after "elements.size() == 2"
  will make the code more readable

In simpleConcat(),
  should use a local variable 'mh', like the newString or newArrayWithSuffix

Can you explain me, what rebind is exactly ?

Rémi 

----- Mail original -----
> De: "Claes Redestad" <claes.redestad at oracle.com>
> À: "core-libs-dev" <core-libs-dev at openjdk.java.net>
> Envoyé: Vendredi 29 Mai 2020 17:05:19
> Objet: RFR: 8246152: Improve String concat bootstrapping

> Hi,
> 
> a few small simplifications and optimizations to StringConcatFactory:
> 
> - refactor makeConcat/makeConcatWithArguments methods to remove the
>   generateRecipe argument
> - fold back-to-back constants into one when parsing recipe, which
>   allows the prepender logic to be simplified
> - do input checking in the parse pass
> - get rid of the Recipe and RecipeElement classes by representing the
> parsed recipe as a list of Strings which are either null (argument slot)
> or not (constant)
> - eagerly rebind on setup of those method handles that we'll always
> transform (transforming will call rebind() anyway which will now be a no-op)
> - simplify filtering logic by picking up the erased type, so that we can
> do c == Object.class rather than !c.isPrimitive
> 
> Also adding a microbenchmark I used to step by step verify the fixes
> having a real and measurable effect[1], while verifying a few percent
> improvement on a few existing startup tests[2].
> 
> Bug:    https://bugs.openjdk.java.net/browse/JDK-8246152
> Webrev: http://cr.openjdk.java.net/~redestad/8246152/open.00/
> 
> Testing: tier1
> 
> Thanks!
> 
> /Claes
> 
> [1]
> java -jar build/linux-x64/images/test/micro/benchmarks.jar
> StringConcatFactoryBootstraps -f 2 -w 5 -r 5 -prof gc -jvmArgs=-Xmx1g
> 
> Before:
> Benchmark Mode Cnt Score Error Units
> StringConcatFactoryBootstraps.makeConcatWithConstants avgt 10 3046.855 ±
> 62.981 ns/op
> StringConcatFactoryBootstraps.makeConcatWithConstants:·gc.alloc.rate.norm
> avgt 10 4596.214 ± 121.121 B/op
> 
> After:
> Benchmark Mode Cnt Score Error Units
> StringConcatFactoryBootstraps.makeConcatWithConstants avgt 10 2764.634 ±
> 56.244 ns/op
> StringConcatFactoryBootstraps.makeConcatWithConstants:·gc.alloc.rate.norm
> avgt 10 4136.187 ± 0.013 B/op
> 
> [2]
> http://cr.openjdk.java.net/~redestad/scratch/erase_scf_types.00/ObjStringCombos.java
> 
> Before:
>      3,661,949,568      instructions              #    1.09  insn per
> cycle           ( +-  1.04% )
>        728,280,499      branches                  #  492.540 M/sec
>               ( +-  1.06% )
>         30,496,964      branch-misses             #    4.19% of all
> branches          ( +-  0.93% )
> 
>        0.301502707 seconds time elapsed
>          ( +-  1.04% )
> 
> After:
>      3,485,679,714      instructions              #    1.09  insn per
> cycle           ( +-  0.90% )
>        692,247,529      branches                  #  491.822 M/sec
>               ( +-  0.92% )
>         28,939,534      branch-misses             #    4.18% of all
> branches          ( +-  0.90% )
> 
>        0.291642667 seconds time elapsed
>           ( +-  0.93% )