hg: jdk/sandbox: 8222852: Reduce String concat combinator tree shapes by folding constants into prependers

[chris.hegarty at oracle.com]

Changeset: 1cb0306f16d1
Author:    redestad
Date:      2019-04-30 12:54 +0200
URL:       http://hg.openjdk.java.net/jdk/sandbox/rev/1cb0306f16d1

8222852: Reduce String concat combinator tree shapes by folding constants into prependers
Reviewed-by: shade, plevart, forax
Contributed-by: claes.redestad at oracle.com, peter.levart at gmail.com

! src/java.base/share/classes/java/lang/StringConcatHelper.java
! src/java.base/share/classes/java/lang/invoke/StringConcatFactory.java
- test/jdk/java/lang/String/concat/StringConcatFactoryEmptyMethods.java
+ test/jdk/java/lang/String/concat/StringConcatFactoryRepeatedConstants.java
! test/micro/org/openjdk/bench/java/lang/StringConcat.java