RFR: 8333893: Optimization for StringBuilder append boolean & null [v8]

[Shaojin Wen]

On Thu, 13 Jun 2024 09:51:21 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> Shaojin Wen has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - rename benchmark
>>  - code format & use long address
>
> Replacing `StringUTF16.putChar` with an `Unsafe.putByte` construct seems safe since the former already depends on bounds checks having been done elsewhere. Replacing `byte[]` stores with `Unsafe.putByte` requires a thorough examination as that would drop implicit bounds checks.  
> 
> On my M1 laptop I get similar numbers:
> 
> Name                                 Cnt  Base   Error   Test   Error  Unit  Change
> StringBuilders.appendWithBool8Latin1  15 7,500 ± 0,072  6,112 ± 0,049 ns/op   1,23x (p = 0,000*)
> StringBuilders.appendWithBool8Utf16   15 9,650 ± 0,021  7,304 ± 0,047 ns/op   1,32x (p = 0,000*)
> StringBuilders.appendWithNull8Latin1  15 7,118 ± 0,033  5,158 ± 0,062 ns/op   1,38x (p = 0,000*)
> StringBuilders.appendWithNull8Utf16   15 9,336 ± 0,083  6,870 ± 0,069 ns/op   1,36x (p = 0,000*)
>   * = significant
> 
> 
> On a linux-x64 workstation some of the micros regress, though:
> 
> Name                                 Cnt   Base    Error    Test   Error  Unit  Change
> StringBuilders.appendWithBool8Latin1  15 10.781 ±  0.236  16.279 ± 1.087 ns/op   0.66x (p = 0.000*)
> StringBuilders.appendWithBool8Utf16   15 22.942 ±  0.405  23.733 ± 0.792 ns/op   0.97x (p = 0.001*)
> StringBuilders.appendWithNull8Latin1  15 24.313 ± 10.479  24.397 ± 7.483 ns/op   1.00x (p = 0.979 )
> StringBuilders.appendWithNull8Utf16   15 38.704 ±  5.972  27.542 ± 5.620 ns/op   1.41x (p = 0.000*)
>   * = significant
> 
> 
> `-XX:+TraceMergeStores` seem to indicate the merging happens as it should in each case:
> 
> 
> [TraceMergeStores]: Replace
>  2493  StoreB  === 1387 5370 2980 2939  [[ 1962 ]]  @byte[int:>=0] (java/lang/Cloneable,java/io/Serializable):exact+any *, idx=13; unsafe  Memory: @byte[int:>=0] (java/lang/Cloneable,java/io/Serializable):NotNull:exact[2] *, idx=13; !jvms: StringLatin1::putCharsAt @ bci:50 (line 834) AbstractStringBuilder::appendNull @ bci:34 (line 642) AbstractStringBuilder::append @ bci:5 (line 587) StringBuilder::append @ bci:2 (line 179) StringBuilders::appendWithNull8Latin1 @ bci:38 (line 267) StringBuilders_appendWithNull8Latin1_jmhTest::appendWithNull8Latin1_avgt_jmhStub @ bci:17 (line 190)
>  1962  StoreB  === 1387 2493 2494 2442  [[ 1388 ]]  @byte[int:>=0] (java/lang/Cloneable,java/io/Serializable):exact+any *, idx=13; unsafe  Memory: @byte[int:>=0] (java/lang/Cloneable,java/io/Serializable):NotNull:exact[2] *, idx=13; !jvms: StringLatin1::putCharsAt @ bci:62 (line 835) AbstractStringBuilder::appendNull @ bci:34 (line 642) AbstractStringBuilder::append @ bci:5 (line 587) StringBuilder::append...

The performance regression issue on x64 platform has been fixed. Please continue to review @cl4es @liach

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PR Comment: https://git.openjdk.org/jdk/pull/19626#issuecomment-2179620100