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

[Ivan Gerasimov]

Hello Tagir!


On 4/30/19 8:57 AM, Tagir Valeev wrote:
> 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.

Good point!  Will do.

With kind regards,
Ivan

> 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

-- 
With kind regards,
Ivan Gerasimov