machine: 2 CPUs, Intel(R) Xeon(R) Processor @ 2.10GHz

$ java  org.openjdk.jmh.Main -f 2 -wi 3 -w 1 -i 5 -r 1     (25.0.4.1+1-LTS, JMH 1.37)
Benchmark                             Mode  Cnt    Score    Error  Units
StringBench.compareToLastCharDiffers  avgt   10   13.515 ±  0.096  ns/op
StringBench.concatTwo                 avgt   10   75.682 ±  1.184  ns/op
StringBench.equalsSameContent         avgt   10    8.563 ±  0.179  ns/op
StringBench.indexOfAbsentString       avgt   10   36.571 ±  0.238  ns/op
StringBench.indexOfLastChar           avgt   10    2.872 ±  0.092  ns/op
StringBench.toUpper                   avgt   10  276.137 ± 11.187  ns/op

$ java -XX:-CompactStrings org.openjdk.jmh.Main -f 2 -wi 3 -w 1 -i 5 -r 1     (25.0.4.1+1-LTS, JMH 1.37)
Benchmark                             Mode  Cnt    Score    Error  Units
StringBench.compareToLastCharDiffers  avgt   10   16.630 ±  1.244  ns/op
StringBench.concatTwo                 avgt   10  142.990 ±  2.788  ns/op
StringBench.equalsSameContent         avgt   10   14.370 ±  0.857  ns/op
StringBench.indexOfAbsentString       avgt   10   71.265 ±  1.693  ns/op
StringBench.indexOfLastChar           avgt   10    3.677 ±  0.308  ns/op
StringBench.toUpper                   avgt   10  558.868 ± 21.992  ns/op