RFR: 8220159: Optimize various RegMask operations by introducing watermarks

[Nils Eliasson]

Hi Claes,

Terrific work!

Reviewed,

Nils

On 2019-03-05 16:54, Claes Redestad wrote:
> Hi,
>
> by introducing a low and high water mark of the RegMask words that we
> are sure have register bits, we can reduce time spent doing a variety of
> operations.
>
> Bug:    https://bugs.openjdk.java.net/browse/JDK-8220159
> Webrev: http://cr.openjdk.java.net/~redestad/8220159/open.00/
>
> On a few profiled startup application the average number of instructions
> spent compiling methods in C2 drops 10-15%, and we see improvements on a
> range of startup and footprint applications.
>
> There are also a few improvements on microbenchmarks, likely due to a
> positive effect on warmup times.
>
> Testing: tier1-3
>
> Thanks!
>
> /Claes