RFR: 8196334: Optimize UUID#fromString

[Peter Levart]

Hi,

When I noticed this optimization, I had some ideas how to push this even 
further, but only now had some time to try them out.

Here are some incremental improvements [1] to the already brilliant idea 
with the following JMH results (the baseline is JDK build with patch for 
8196334 already applied):

Benchmark                     (size)   Mode  Cnt   Score   Error Units
UUIDBench.uuidFromString       20000  thrpt    5  37.344 ± 0.257 ops/us
UUIDBench.uuidFromStringAlt1   20000  thrpt    5  29.069 ± 0.137 ops/us
UUIDBench.uuidFromStringAlt2   20000  thrpt    5  27.308 ± 0.204 ops/us
UUIDBench.uuidFromStringAlt3   20000  thrpt    5  23.195 ± 0.885 ops/us

As can be seen, the trick was to eliminate branches (alt1, alt2) and to 
reduce the number of operations (shifts) in alt3. One last trick in alt3 
was to use the array length in a check that is then fused with array 
index bounds check (I think) so that we get one of them for free.

What do you think? Is this good enough to warrant another change? As you 
can see, I haven't prepared the patch yet,  just benchmark.

Regards, Peter

[1] 
http://cr.openjdk.java.net/~plevart/jdk-dev/8196334_UUID.fromString/UUIDBench.java


On 3/2/20 8:26 AM, Claes Redestad wrote:
> On 2020-03-02 08:14, Alan Bateman wrote:
>>>
>>> http://cr.openjdk.java.net/~redestad/8196334/open.02/
>> Looks good.
>
> Thanks - pushed!
>
> /Claes