RFR 8222955 : Optimize String.replace(CharSequence, CharSequence) for Latin1 encoded strings

[Tagir Valeev]

Hello!

New webrev looks good. Probably it worth adding a testcase for
overflow (assert that OOME is thrown)? I guess, something like
"1".repeat(65536).replace("1", "1".repeat(65536)) would produce OOME
quite fast and without allocating much memory.

With best regards,
Tagir Valeev.

On Tue, Apr 30, 2019 at 11:43 AM Ivan Gerasimov
<ivan.gerasimov at oracle.com> wrote:
>
> Hello everyone!
>
> Please help review the second version of the enhancement.
> A separate branch was added to handle UTF16 in the searched string and/or in the target and replacement.
>
> Switching to Math.xxxExact() suggested by Tagir gave ~4% of throughput on affected test cases.
>
> Also, allocating uninitialized array added ~7% for Latin1 strings.
> I used StringConcatHelper.newArray() to avoid bringing Unsafe into StringLatin1.
> In the StringLatin1.replace(), the newly allocated array is guaranteed to be filled up, and the filling code should never throw, so I believe using uninitialized arrays here is justified.
>
> Here's the updated webrev:
> http://cr.openjdk.java.net/~igerasim/8222955/01/webrev/
>
> Below please find the benchmark numbers (with an additional column, showing the improvement.)
>
> Surprisingly, in one test case a slowdown was observed:  Only for Latin1 string, with 1-char target, when the target string was *not* found.
> If I understood it correctly, this is because prior the fix the intrinsified StringLatin1.indexOf(byte[], byte[]) was called on the first place, so there were effectively a fast path for exactly this pattern.
>
> I'm not quite sure what to do about it.
> Maybe this is fine as it is, since the *average* improvement across different test cases is still good?
>
>
>  - prior fix:
> Benchmark                          Mode  Cnt    Score   Error  Units
> StringReplace.replace0x1_1_Latin1  avgt   15    7.116 ± 0.060  ns/op
> StringReplace.replace0x1_1_UTF16   avgt   15   84.255 ± 3.381  ns/op
> StringReplace.replace1x1_0_Latin1  avgt   15   63.254 ± 0.973  ns/op
> StringReplace.replace1x1_0_UTF16   avgt   15   89.941 ± 3.210  ns/op
> StringReplace.replace1x1_1_Latin1  avgt   15   75.662 ± 0.344  ns/op
> StringReplace.replace1x1_1_UTF16   avgt   15   81.454 ± 1.986  ns/op
> StringReplace.replace1x1_2_Latin1  avgt   15   89.492 ± 1.889  ns/op
> StringReplace.replace1x1_2_UTF16   avgt   15   87.430 ± 1.341  ns/op
> StringReplace.replace2x1_0_Latin1  avgt   15   69.575 ± 0.368  ns/op
> StringReplace.replace2x1_0_UTF16   avgt   15  112.201 ± 2.836  ns/op
> StringReplace.replace2x1_1_Latin1  avgt   15   83.841 ± 0.940  ns/op
> StringReplace.replace2x1_1_UTF16   avgt   15  115.722 ± 2.267  ns/op
> StringReplace.replace2x1_2_Latin1  avgt   15   99.266 ± 1.008  ns/op
> StringReplace.replace2x1_2_UTF16   avgt   15  132.271 ± 2.365  ns/op
>
>
>  - after fix:
> Benchmark                          Mode  Cnt   Score   Error  Units
> StringReplace.replace0x1_1_Latin1  avgt   15  10.541 ± 0.826  ns/op   x0.68
> StringReplace.replace0x1_1_UTF16   avgt   15  31.473 ± 0.389  ns/op   x2.68
> StringReplace.replace1x1_0_Latin1  avgt   15  50.455 ± 5.038  ns/op   x1.25
> StringReplace.replace1x1_0_UTF16   avgt   15  35.355 ± 0.074  ns/op   x2.54
> StringReplace.replace1x1_1_Latin1  avgt   15  22.868 ± 0.076  ns/op   x3.31
> StringReplace.replace1x1_1_UTF16   avgt   15  22.290 ± 1.913  ns/op   x3.65
> StringReplace.replace1x1_2_Latin1  avgt   15  51.362 ± 0.130  ns/op   x1.74
> StringReplace.replace1x1_2_UTF16   avgt   15  33.086 ± 0.088  ns/op   x2.64
> StringReplace.replace2x1_0_Latin1  avgt   15  57.169 ± 7.165  ns/op   x1.22
> StringReplace.replace2x1_0_UTF16   avgt   15  50.886 ± 1.193  ns/op   x2.20
> StringReplace.replace2x1_1_Latin1  avgt   15  23.320 ± 2.954  ns/op   x3.60
> StringReplace.replace2x1_1_UTF16   avgt   15  24.741 ± 0.229  ns/op   x4.68
> StringReplace.replace2x1_2_Latin1  avgt   15  56.045 ± 0.153  ns/op   x1.77
> StringReplace.replace2x1_2_UTF16   avgt   15  49.795 ± 0.178  ns/op   x2.66
>
> --
> With kind regards,
> Ivan Gerasimov