String concatenation tweaks

[Aleksey Shipilev]

On 05/24/2015 06:33 PM, Remi Forax wrote:
> Here is my version (see at the end of this message).

Thanks! Merged it into the patchset with minor polish:
 http://cr.openjdk.java.net/~shade/scratch/string-concat-indy/

The performance is interesting. It seems to break OptimizeStringConcat,
and so it's a performance win only on non-optimized chains, like
string_string_long. The allocation pressure is slightly higher as well,
seems to be because int[] from the collector is not scalarized.

You may want to tune it more, JMH benchmarks are here:
 http://cr.openjdk.java.net/~shade/scratch/string-concat-indy/indy-concat-bench.tar.gz

...and -prof perfasm, -prof perfnorm, and -prof gc are your friends.

Thanks,
-Aleksey

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