RFR: 8224986: (str) optimize StringBuilder.append(CharSequence, int, int) for String arguments

[Roger Riggs]

Hi Claes,

With the use of random, you should log the seed for the possibility to 
repeat a particular case.

Otherwise, looks ok.

Roger


On 05/29/2019 11:43 AM, Jim Laskey wrote:
> +1
>
>> On May 29, 2019, at 12:36 PM, Claes Redestad <claes.redestad at oracle.com> wrote:
>>
>> Hi,
>>
>> it's been pointed out[1] that append(string.substring(start, end)) can
>> outperform append(string, start, end) in some circumstances. In part due
>> the former being intrinsified, but also I think due it tickling some
>> string concat optimizations that allow for eliding the StringBuilder
>> itself completely when there's only one non-constant argument.
>>
>> While not ruling out intrinsification of append(String, int, int), I was
>> able to achieve a reasonable speed-up by peeling off String arguments
>> to append(CharSequence, int, int) and dropping into a routine that uses
>> System.arraycopy when appropriate.
>>
>> This seems like a reasonable improvement in the interim, and an
>> opportunity to incorporate the relevant microbenchmarks.
>>
>> Bug:    https://bugs.openjdk.java.net/browse/JDK-8224986
>> Webrev: http://cr.openjdk.java.net/~redestad/8224986/open.00/
>>
>> I extended and incorporated the microbenchmark provided in [1] to also include variants with UTF16 Strings and mixes of arguments, ensuring
>> speedups on all appendBounds* variants[2].
>>
>> Thanks!
>>
>> /Claes
>>
>> [1] http://mail.openjdk.java.net/pipermail/core-libs-dev/2019-January/057834.html
>> [2]
>> Baseline:
>>
>> Benchmark            (length)  Mode  Cnt     Score     Error   Units
>> appendBounds             1000  avgt   10   576.939 ±  21.125   ns/op
>> ·gc.alloc.rate.norm     1000  avgt   10  2144.000 ±   0.001    B/op
>> appendBoundsMix          1000  avgt   10   855.308 ±  27.071   ns/op
>> ·gc.alloc.rate.norm     1000  avgt   10  3160.000 ±   0.001    B/op
>> appendBoundsUtf16        1000  avgt   10  1424.518 ±  33.319   ns/op
>> ·gc.alloc.rate.norm     1000  avgt   10  5192.000 ±   0.001    B/op
>>
>> Patch:
>>
>> Benchmark            (length)  Mode  Cnt     Score     Error   Units
>> appendBounds             1000  avgt   10   466.640 ±  15.069   ns/op
>> ·gc.alloc.rate.norm     1000  avgt   10  2120.000 ±   0.001    B/op
>> appendBoundsMix          1000  avgt   10   758.886 ±  22.983   ns/op
>> ·gc.alloc.rate.norm     1000  avgt   10  3160.000 ±   0.001    B/op
>> appendBoundsUtf16        1000  avgt   10  1320.360 ±  49.097   ns/op
>> ·gc.alloc.rate.norm     1000  avgt   10  5192.000 ±   0.001    B/op