RFR: 8245756: Reduce bootstrap cost of StringConcatFactory prependers

[Claes Redestad]

Hi Rémi,

in isolation (1) was the bigger win on most of my tests. I can split the
three improvements apart, if you prefer.

Not sure in which sense you mean inlining? Few of the methods in the
bootstrap code are likely hot enough to see inlining by a JIT - and the
resulting MHs should be identical, just not constructed over and over
again.

/Claes

On 2020-05-25 22:53, Remi Forax wrote:
> Hi Claes,
> do you have evaluated the improvement (1) in separation of the others ?
> 
> (2) or (3) are clearly improvement but (1) is a trade of because you are adding a second lookup into another table and make prepender() less likely to be inlined.
> 
> Rémi
> 
> ----- Mail original -----
>> De: "Claes Redestad" <claes.redestad at oracle.com>
>> À: "core-libs-dev" <core-libs-dev at openjdk.java.net>
>> Envoyé: Lundi 25 Mai 2020 22:23:23
>> Objet: RFR: 8245756: Reduce bootstrap cost of StringConcatFactory prependers
> 
>> Hi,
>>
>> let's improve the StringConcatFactory a bit!
>>
>> - prependers where both prefix and suffix is null are common in typical
>> expressions; caching these specifically is profitable
>>
>> - current prepender argument ordering is unfortunate: String prefix,
>> <arg>, String suffix. This means we have to do two back-to-back
>> insertArguments rather than one if they were grouped together
>>
>> - add a bridge to the String mix function in StringConcatHelper to avoid
>> method handle invokes in the bootstrap path.
>>
>> Webrev: http://cr.openjdk.java.net/~redestad/8245756/open.00/
>> Bug:    https://bugs.openjdk.java.net/browse/JDK-8245756
>>
>> All together I see a substantial improvement on a number of
>> concatenation bootstrap tests. On one stress test[1] I get these numbers
>> before:
>>
>>       4,257,229,918 instructions # 1.10 insn per cycle ( +- 0.84% )
>>         847,230,764 branches # 504.826 M/sec ( +- 0.87% )
>>          34,600,787 branch-misses # 4.08% of all branches ( +- 0.91% )
>>         0.319545331 seconds time elapsed ( +- 1.18% )
>>
>> And after:
>>
>>       3,692,867,129 instructions # 1.10 insn per cycle ( +- 0.73% )
>>         734,054,515 branches # 498.753 M/sec ( +- 0.74% )
>>          30,699,692 branch-misses # 4.18% of all branches ( +- 0.75% )
>>         0.295842958 seconds time elapsed ( +- 1.10% )
>>
>> So ~13% reduction on this test.
>>
>> Testing: tier1+2
>>
>> Thanks!
>>
>> /Claes
>>
>> [1]
>> http://cr.openjdk.java.net/~redestad/scratch/erase_scf_types.00/ObjStringCombos.java