http://cr.openjdk.java.net/~shade/density/string-density-bench.zip
http://cr.openjdk.java.net/~shade/density/string-density-bench.jar

$ java -jar target/string-density-bench.jar encoding -f 3 -wi 3 -i 3

(add more precise benchmark name after "encoding" to constrain benchmarks)
(add -p encoding=... and/or -p size=... to constrain parameters)

=== UTF-8/From

Benchmark      (encoding)  (size)  Mode  Cnt      Score      Error  Units

# JDK 9 Baseline
From.ascii          UTF-8    4096  avgt    9   1813.472 ±   12.360  ns/op
From.beg_00FF       UTF-8    4096  avgt    9   2734.943 ±   17.374  ns/op
From.beg_FF43       UTF-8    4096  avgt    9   2757.093 ±   22.989  ns/op
From.end_00FF       UTF-8    4096  avgt    9   2730.908 ±   25.934  ns/op
From.end_FF43       UTF-8    4096  avgt    9   2703.780 ±   70.832  ns/op

# Patched, -XX:-CompactStrings
From.ascii          UTF-8    4096  avgt    9   2619.706 ±   37.186  ns/op
From.beg_00FF       UTF-8    4096  avgt    9   2749.935 ±   18.645  ns/op
From.beg_FF43       UTF-8    4096  avgt    9   2755.768 ±   24.121  ns/op
From.end_00FF       UTF-8    4096  avgt    9   2759.387 ±   92.994  ns/op
From.end_FF43       UTF-8    4096  avgt    9   2625.446 ±   26.018  ns/op

Issues:
 *) From.ascii test with -XX:-CS is not returning back to baseline level.

# SD baseline
From.ascii          UTF-8    4096  avgt    9    432.447 ±   15.278  ns/op
From.beg_00FF       UTF-8    4096  avgt    9   2388.569 ±   33.109  ns/op
From.beg_FF43       UTF-8    4096  avgt    9   2905.258 ±  231.059  ns/op
From.end_00FF       UTF-8    4096  avgt    9   2281.112 ±    9.465  ns/op
From.end_FF43       UTF-8    4096  avgt    9   3082.166 ±   11.344  ns/op

# Patched, -XX:+CompactStrings
From.ascii          UTF-8    4096  avgt    9    429.647 ±   19.920  ns/op
From.beg_00FF       UTF-8    4096  avgt    9   2374.979 ±   24.685  ns/op
From.beg_FF43       UTF-8    4096  avgt    9   2915.967 ±  255.949  ns/op
From.end_00FF       UTF-8    4096  avgt    9   2288.545 ±   37.812  ns/op
From.end_FF43       UTF-8    4096  avgt    9   3108.206 ±   14.971  ns/op

No issues.


=== UTF-8/To

Benchmark      (encoding)  (size)  Mode  Cnt      Score      Error  Units

# JDK 9 Baseline
To.ascii            UTF-8    4096  avgt    9   2132.241 ±   15.759  ns/op
To.beg_00FF         UTF-8    4096  avgt    9   3282.173 ±   25.895  ns/op
To.beg_FF43         UTF-8    4096  avgt    9   4028.761 ±   60.334  ns/op
To.end_00FF         UTF-8    4096  avgt    9   2150.415 ±   13.280  ns/op
To.end_FF43         UTF-8    4096  avgt    9   2157.799 ±   17.116  ns/op

# Patched, -XX:-CompactStrings
To.ascii            UTF-8    4096  avgt    9   2938.611 ±   35.227  ns/op
To.beg_00FF         UTF-8    4096  avgt    9   4097.243 ±   63.274  ns/op
To.beg_FF43         UTF-8    4096  avgt    9   4905.990 ±  170.744  ns/op
To.end_00FF         UTF-8    4096  avgt    9   2942.579 ±   25.674  ns/op
To.end_FF43         UTF-8    4096  avgt    9   2969.094 ±   32.423  ns/op

Issues:
 *) Almost all tests are not returning to baseline level.


# SD baseline
To.ascii            UTF-8    4096  avgt    9   2907.588 ±   16.363  ns/op
To.beg_00FF         UTF-8    4096  avgt    9   4032.347 ±   24.569  ns/op
To.beg_FF43         UTF-8    4096  avgt    9   4566.033 ±   53.746  ns/op
To.end_00FF         UTF-8    4096  avgt    9   2921.026 ±   13.361  ns/op
To.end_FF43         UTF-8    4096  avgt    9   2955.212 ±   49.612  ns/op

# Patched, -XX:+CompactStrings
To.ascii            UTF-8    4096  avgt    9    426.043 ±    9.371  ns/op
To.beg_00FF         UTF-8    4096  avgt    9   4042.002 ±   29.074  ns/op
To.beg_FF43         UTF-8    4096  avgt    9   4594.469 ±  192.615  ns/op
To.end_00FF         UTF-8    4096  avgt    9   2966.955 ±   25.135  ns/op
To.end_FF43         UTF-8    4096  avgt    9   2969.876 ±   52.524  ns/op

No issues.



=== UTF-16/From

Benchmark      (encoding)  (size)  Mode  Cnt      Score      Error  Units

# JDK 9 baseline
From.ascii         UTF-16    4096  avgt    9  13556.418 ±  877.297  ns/op
From.beg_00FF      UTF-16    4096  avgt    9  13252.383 ±  179.153  ns/op
From.beg_FF43      UTF-16    4096  avgt    9  13238.729 ±  131.864  ns/op
From.end_00FF      UTF-16    4096  avgt    9  13323.692 ±  109.823  ns/op
From.end_FF43      UTF-16    4096  avgt    9  13684.421 ± 2040.777  ns/op

# Patched, -XX:-CompactStrings
From.ascii         UTF-16    4096  avgt    9  13305.095 ±  130.302  ns/op
From.beg_00FF      UTF-16    4096  avgt    9  13356.803 ±  191.065  ns/op
From.beg_FF43      UTF-16    4096  avgt    9  13342.801 ±  444.266  ns/op
From.end_00FF      UTF-16    4096  avgt    9  13327.449 ±  215.131  ns/op
From.end_FF43      UTF-16    4096  avgt    9  13326.647 ±  302.509  ns/op

No issues.


# SD Baseline
From.ascii         UTF-16    4096  avgt    9  12871.428 ±  162.275  ns/op
From.beg_00FF      UTF-16    4096  avgt    9  13040.963 ±  728.920  ns/op
From.beg_FF43      UTF-16    4096  avgt    9  13484.810 ±  447.801  ns/op
From.end_00FF      UTF-16    4096  avgt    9  12957.423 ±  688.531  ns/op
From.end_FF43      UTF-16    4096  avgt    9  13590.109 ±  325.016  ns/op

# Patched, -XX:+CompactStrings
From.ascii         UTF-16    4096  avgt    9  13000.952 ±  409.589  ns/op
From.beg_00FF      UTF-16    4096  avgt    9  13316.081 ± 2454.769  ns/op
From.beg_FF43      UTF-16    4096  avgt    9  13588.976 ± 1214.578  ns/op
From.end_00FF      UTF-16    4096  avgt    9  12872.211 ±  124.235  ns/op
From.end_FF43      UTF-16    4096  avgt    9  13658.163 ±  211.070  ns/op

No issues.


=== UTF-16/To

Benchmark      (encoding)  (size)  Mode  Cnt      Score      Error  Units

# JDK 9 baseline
To.ascii           UTF-16    4096  avgt    9   6380.390 ±  399.404  ns/op
To.beg_00FF        UTF-16    4096  avgt    9   6207.107 ±   19.867  ns/op
To.beg_FF43        UTF-16    4096  avgt    9   9681.787 ± 8576.288  ns/op
To.end_00FF        UTF-16    4096  avgt    9   6255.891 ±   89.767  ns/op
To.end_FF43        UTF-16    4096  avgt    9   6288.601 ±  351.498  ns/op

# Patched, -XX:-CompactStrings
To.ascii           UTF-16    4096  avgt    9   6986.680 ±   38.000  ns/op
To.beg_00FF        UTF-16    4096  avgt    9   6958.777 ±   18.865  ns/op
To.beg_FF43        UTF-16    4096  avgt    9  10584.699 ± 8259.775  ns/op
To.end_00FF        UTF-16    4096  avgt    9  10453.951 ± 8679.397  ns/op
To.end_FF43        UTF-16    4096  avgt    9   7043.708 ±  199.714  ns/op

Issues:
 *) Almost all tests are not returning to baseline level.
 *) (Some run-to-run variance is observed)


# SD Baseline
To.ascii           UTF-16    4096  avgt    9   7108.013 ±   70.826  ns/op
To.beg_00FF        UTF-16    4096  avgt    9  10538.816 ± 8550.993  ns/op
To.beg_FF43        UTF-16    4096  avgt    9  13940.282 ± 8586.786  ns/op
To.end_00FF        UTF-16    4096  avgt    9   7481.672 ±  955.146  ns/op
To.end_FF43        UTF-16    4096  avgt    9   7225.158 ±  428.748  ns/op

# Patched, -XX:+CompactStrings
To.ascii           UTF-16    4096  avgt    9   7090.758 ±   45.910  ns/op
To.beg_00FF        UTF-16    4096  avgt    9   7137.101 ±  248.284  ns/op
To.beg_FF43        UTF-16    4096  avgt    9   7205.252 ±  495.074  ns/op
To.end_00FF        UTF-16    4096  avgt    9   7144.024 ±  317.968  ns/op
To.end_FF43        UTF-16    4096  avgt    9   7047.074 ±   93.236  ns/op

No issues.


=== ISO-8859-1/From

Benchmark      (encoding)  (size)  Mode  Cnt      Score      Error  Units

# JDK 9 baseline
From.ascii     ISO-8859-1    4096  avgt    9   1854.618 ±   16.214  ns/op
From.beg_00FF  ISO-8859-1    4096  avgt    9   1855.655 ±   15.273  ns/op
From.beg_FF43  ISO-8859-1    4096  avgt    9   1863.509 ±   29.172  ns/op
From.end_00FF  ISO-8859-1    4096  avgt    9   1847.640 ±   10.851  ns/op
From.end_FF43  ISO-8859-1    4096  avgt    9   1851.610 ±   14.257  ns/op

# Patched, -XX:-CompactStrings
From.ascii     ISO-8859-1    4096  avgt    9   2310.909 ±    6.424  ns/op
From.beg_00FF  ISO-8859-1    4096  avgt    9   2319.014 ±   27.928  ns/op
From.beg_FF43  ISO-8859-1    4096  avgt    9   2565.613 ±  311.246  ns/op
From.end_00FF  ISO-8859-1    4096  avgt    9   2316.846 ±   13.149  ns/op
From.end_FF43  ISO-8859-1    4096  avgt    9   2559.515 ±  331.928  ns/op

Issues:
 *) Almost all tests are not returning to baseline level.


# SD Baseline
From.ascii     ISO-8859-1    4096  avgt    9    409.730 ±    4.142  ns/op
From.beg_00FF  ISO-8859-1    4096  avgt    9    408.972 ±    1.705  ns/op
From.beg_FF43  ISO-8859-1    4096  avgt    9    409.021 ±    2.535  ns/op
From.end_00FF  ISO-8859-1    4096  avgt    9    408.639 ±    3.234  ns/op
From.end_FF43  ISO-8859-1    4096  avgt    9    406.365 ±    5.721  ns/op

# Patched, -XX:+CompactStrings
From.ascii     ISO-8859-1    4096  avgt    9    424.231 ±   27.785  ns/op
From.beg_00FF  ISO-8859-1    4096  avgt    9   2709.812 ±   24.869  ns/op
From.beg_FF43  ISO-8859-1    4096  avgt    9    441.024 ±   13.163  ns/op
From.end_00FF  ISO-8859-1    4096  avgt    9   2773.211 ±   17.219  ns/op
From.end_FF43  ISO-8859-1    4096  avgt    9    434.324 ±   11.307  ns/op

Issues:
 *) All tests are regressing! It would seem we lost the fast-path to plain
copy, and instead doing this:

    private static class sun/nio/cs/ISO_8859_1.Decoder extends CharsetDecoder
                                 implements ArrayDecoder {
        public int decode(byte[] src, int sp, int len, char[] dst) {
            if (len > dst.length)
                len = dst.length;
            int dp = 0;
            while (dp < len)
                dst[dp++] = (char)(src[sp++] & 0xff);
            return dp;
        }
   }


=== ISO-8859-1/To

Benchmark      (encoding)  (size)  Mode  Cnt      Score      Error  Units

# JDK 9 baseline
To.ascii       ISO-8859-1    4096  avgt    9    373.911 ±    6.524  ns/op
To.beg_00FF    ISO-8859-1    4096  avgt    9    375.138 ±    7.099  ns/op
To.beg_FF43    ISO-8859-1    4096  avgt    9    380.838 ±    4.333  ns/op
To.end_00FF    ISO-8859-1    4096  avgt    9    372.919 ±    8.642  ns/op
To.end_FF43    ISO-8859-1    4096  avgt    9    399.107 ±    5.228  ns/op

# Patched, -XX:-CompactStrings
To.ascii       ISO-8859-1    4096  avgt    9   1153.573 ±    6.029  ns/op
To.beg_00FF    ISO-8859-1    4096  avgt    9   1158.133 ±   10.280  ns/op
To.beg_FF43    ISO-8859-1    4096  avgt    9   1167.302 ±   11.072  ns/op
To.end_00FF    ISO-8859-1    4096  avgt    9   1158.010 ±   10.968  ns/op
To.end_FF43    ISO-8859-1    4096  avgt    9   1161.513 ±    8.947  ns/op

Issues:
 *) Almost all tests are not returning to baseline level.


# SD Baseline
To.ascii       ISO-8859-1    4096  avgt    9   1138.785 ±   14.830  ns/op
To.beg_00FF    ISO-8859-1    4096  avgt    9   1139.529 ±    9.486  ns/op
To.beg_FF43    ISO-8859-1    4096  avgt    9   1165.575 ±   13.798  ns/op
To.end_00FF    ISO-8859-1    4096  avgt    9   1138.156 ±    8.041  ns/op
To.end_FF43    ISO-8859-1    4096  avgt    9   1167.203 ±    8.646  ns/op

# Patched, -XX:+CompactStrings
To.ascii       ISO-8859-1    4096  avgt    9    422.241 ±   14.226  ns/op
To.beg_00FF    ISO-8859-1    4096  avgt    9   1139.888 ±   10.081  ns/op
To.beg_FF43    ISO-8859-1    4096  avgt    9   1159.927 ±   11.434  ns/op
To.end_00FF    ISO-8859-1    4096  avgt    9   1197.651 ±   13.931  ns/op
To.end_FF43    ISO-8859-1    4096  avgt    9   1164.348 ±    9.006  ns/op

No issues.