RFR [9] 8151384: Examine sun.misc.ASCIICaseInsensitiveComparator

[Aleksey Shipilev]

Hi,

On 03/07/2016 07:29 PM, Chris Hegarty wrote:
> What is in the webrev is specialized versions of compare when
> the coder of the strings match. Alternatively, this could be pushed
> down to String[Latin1|UTF16].
> 
> Webrev & bug:
>   http://cr.openjdk.java.net/~chegar/8151384/webrev.00/
>   https://bugs.openjdk.java.net/browse/JDK-8151384

Overall, good cleanup idea. I think the actual helpers deserve to be
pushed to String[Latin1|UTF16], as String is already overloaded with
lots of code. See how e.g. String.regionMatches(boolean ignoreCase, int
toffset, String other, int ooffset, int len) does it.

Nits:

 *) Change:  compareLatin1ToUTF16(v2, v1) * -1;
        To: -compareLatin1ToUTF16(v2, v1);

 *) Do we really need to cast up/down to "char" in compareLatin1*?


> Benchmarks and results ( based, somewhat, on Aleksey's [1] ):
>   http://cr.openjdk.java.net/~chegar/8151384/bench/

Comments on benchmarks (that might have impact on validity):

 *) "# JMH 1.6 (released 388 days ago, please consider updating!)"

 *) CaseInsensitiveCompare.cmp1_cmp1 is suspiciously unaffected by size.
That's because benchmark goes through the identity comparison:

    @Benchmark
    @CompilerControl(CompilerControl.Mode.DONT_INLINE)
    public int cmp1_cmp1() {
        return CASE_INSENSITIVE_ORDER.compare(cmp1_1, cmp1_1);
    }

...should really be:

    @Benchmark
    @CompilerControl(CompilerControl.Mode.DONT_INLINE)
    public int cmp1_cmp1() {
        return CASE_INSENSITIVE_ORDER.compare(cmp1_1, cmp1_2);
    }

 *) Probable dead-code elimination here:

    @Benchmark
    @CompilerControl(CompilerControl.Mode.DONT_INLINE)
    public void StringCaseInsensitiveComparator() {
        List<String> strings = AVAILABLE_CHARSETS;
        for (String s1 : strings) {
            for (String s2 : strings) {
                 String.CASE_INSENSITIVE_ORDER.compare(s1, s2);
            }
        }
    }

...should be:

    @Benchmark
    @CompilerControl(CompilerControl.Mode.DONT_INLINE)
    public void StringCaseInsensitiveComparator(Blackhole bh) {
        List<String> strings = AVAILABLE_CHARSETS;
        for (String s1 : strings) {
            for (String s2 : strings) {
                 bh.consume(String.CASE_INSENSITIVE_ORDER.compare(s1, s2));
            }
        }
    }


Thanks,
-Aleksey