RFR: 8301958: Reduce Arrays.copyOf/-Range overheads [v7]

[David Schlosnagle]

On Wed, 8 Feb 2023 00:07:14 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> This patch adds special-cases to `Arrays.copyOf` and `Arrays.copyOfRange` to clone arrays when `newLength` or range inputs span the input array. This helps eliminate range checks and has been verified to help various String operations. Example:
>> 
>> Baseline
>> 
>> Benchmark                                            (size)  Mode  Cnt   Score   Error  Units
>> StringConstructor.newStringFromArray                      7  avgt   15  16.817 ± 0.369  ns/op
>> StringConstructor.newStringFromArrayWithCharset           7  avgt   15  16.866 ± 0.449  ns/op
>> StringConstructor.newStringFromArrayWithCharsetName       7  avgt   15  22.198 ± 0.396  ns/op
>> 
>> Patch: 
>> 
>> Benchmark                                            (size)  Mode  Cnt   Score   Error  Units
>> StringConstructor.newStringFromArray                      7  avgt   15  14.666 ± 0.336  ns/op
>> StringConstructor.newStringFromArrayWithCharset           7  avgt   15  14.582 ± 0.288  ns/op
>> StringConstructor.newStringFromArrayWithCharsetName       7  avgt   15  20.339 ± 0.328  ns/op
>
> Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Minimize, force inline, generalize

I'm also curious if returning the new length from `checkLength` would be worthwhile

src/java.base/share/classes/java/util/Arrays.java line 3823:

> 3821:         if (to - from < 0) {
> 3822:             throw new IllegalArgumentException(from + " > " + to);
> 3823:         }

Would it be beneficial to return the difference of `to` and `from` for caller use?

Suggestion:

    private static int checkLength(int from, int to) {
        int newLength = to - from;
        if (newLength < 0) {
            throw new IllegalArgumentException(from + " > " + to);
        }
        return newLength;

src/java.base/share/classes/java/util/Arrays.java line 3870:

> 3868:     private static byte[] copyOfRangeGeneric(byte[] original, int from, int to) {
> 3869:         checkLength(from, to);
> 3870:         int newLength = to - from;

```suggestion        
        int newLength = checkLength(from, to);

src/java.base/share/classes/java/util/Arrays.java line 3914:

> 3912:     private static short[] copyOfRangeGeneric(short[] original, int from, int to) {
> 3913:         checkLength(from, to);
> 3914:         int newLength = to - from;

Suggestion:

        int newLength = checkLength(from, to);

src/java.base/share/classes/java/util/Arrays.java line 3958:

> 3956:     private static int[] copyOfRangeGeneric(int[] original, int from, int to) {
> 3957:         checkLength(from, to);
> 3958:         int newLength = to - from;

Suggestion:

        int newLength = checkLength(from, to);

src/java.base/share/classes/java/util/Arrays.java line 4002:

> 4000:     private static long[] copyOfRangeGeneric(long[] original, int from, int to) {
> 4001:         checkLength(from, to);
> 4002:         int newLength = to - from;

Suggestion:

        int newLength = checkLength(from, to);

src/java.base/share/classes/java/util/Arrays.java line 4046:

> 4044:     private static char[] copyOfRangeGeneric(char[] original, int from, int to) {
> 4045:         checkLength(from, to);
> 4046:         int newLength = to - from;

Suggestion:

        int newLength = checkLength(from, to);

src/java.base/share/classes/java/util/Arrays.java line 4091:

> 4089:     private static float[] copyOfRangeGeneric(float[] original, int from, int to) {
> 4090:         checkLength(from, to);
> 4091:         int newLength = to - from;

Suggestion:

        int newLength = checkLength(from, to);

src/java.base/share/classes/java/util/Arrays.java line 4142:

> 4140:     private static double[] copyOfRangeGeneric(double[] original, int from, int to) {
> 4141:         checkLength(from, to);
> 4142:         int newLength = to - from;

Suggestion:

        int newLength = checkLength(from, to);

src/java.base/share/classes/java/util/Arrays.java line 4193:

> 4191:     private static boolean[] copyOfRangeGeneric(boolean[] original, int from, int to) {
> 4192:         checkLength(from, to);
> 4193:         int newLength = to - from;

Suggestion:

        int newLength = checkLength(from, to);

-------------

PR: https://git.openjdk.org/jdk/pull/12453