RFR: 8222484: Specialize generation of simple String concatenation expressions

[Jim Laskey]

The StringConcatHelper::valueOf really should be StringConcatHelper::stringOf to clarify the result. Use here is unlike String::valueOf context where the result is logically String.

StringConcatHelper::mix comments really should describe the encoding. If does a lot of handwaving re checking for overflow and mixing coder.

Cheers,

-- Jim







> On Apr 15, 2019, at 7:49 AM, Claes Redestad <claes.redestad at oracle.com> wrote:
> 
> Hi,
> 
> please review this enhancement to specialize a few simple and common
> String concatenation patterns in the default strategy.
> 
> Bug:    https://bugs.openjdk.java.net/browse/JDK-8222484
> Webrev: http://cr.openjdk.java.net/~redestad/8222484/open.00/
> 
> This reduces first-time bootstrap times for the targeted patterns from
> ~20ms to be lost in the noise on my machine (so ~0.5ms), while being
> peak performance neutral and not regressing bootstrap characteristics on
> more complex patterns.
> 
> This also consolidates the String::concat method to reuse the optimized
> method in StringConcatHelper, which speeds up that method by ~1.4x for a
> few sampled inputs.
> 
> Testing: tier1-3
> 
> Thanks!
> 
> /Claes