RFR: 8268231: Aarch64: Use ldp in intrinsics for String.compareTo [v5]

[Nick Gasson]

On Tue, 3 Aug 2021 13:33:07 GMT, Wang Huang <whuang at openjdk.org> wrote:

>> Dear all, 
>>     Can you do me a favor to review this patch. This patch use `ldp` to implement String.compareTo.
>>    
>> * We add a JMH test case 
>> * Here is the result of this test case
>>  
>> Benchmark	                       |(size)| Mode| Cnt|Score | Error	 |Units	
>> ---------------------------------|------|-----|----|------|--------|-----
>> StringCompare.compareLL       |  64  | avgt| 5  |7.992 | ±	0.005|us/op
>> StringCompare.compareLL       |  72  | avgt| 5  |15.029| ±	0.006|us/op
>> StringCompare.compareLL       |  80  | avgt| 5  |14.655| ±	0.011|us/op
>> StringCompare.compareLL       |  91  | avgt| 5  |16.363| ±	0.12 |us/op
>> StringCompare.compareLL       |  101 | avgt| 5  |16.966| ±	0.007|us/op
>> StringCompare.compareLL       |  121 | avgt| 5  |19.276| ±	0.006|us/op
>> StringCompare.compareLL       |  181 | avgt| 5  |19.002| ±	0.417|us/op
>> StringCompare.compareLL       |  256 | avgt| 5  |24.707| ±	0.041|us/op
>> StringCompare.compareLLWithLdp|  64  | avgt| 5  |8.001	| ±	0.121|us/op
>> StringCompare.compareLLWithLdp|  72  | avgt| 5  |11.573| ±	0.003|us/op
>> StringCompare.compareLLWithLdp|  80  | avgt| 5  |6.861 | ±	0.004|us/op
>> StringCompare.compareLLWithLdp|  91  | avgt| 5  |12.774| ±	0.201|us/op
>> StringCompare.compareLLWithLdp|  101 | avgt| 5  |8.691 | ±	0.004|us/op
>> StringCompare.compareLLWithLdp|  121 | avgt| 5  |11.091| ±	1.342|us/op
>> StringCompare.compareLLWithLdp|  181 | avgt| 5  |14.64 | ±	0.581|us/op
>> StringCompare.compareLLWithLdp|  256 | avgt| 5  |25.879| ±	1.775|us/op
>> StringCompare.compareUU       |  64  | avgt| 5  |13.476| ±	0.01 |us/op
>> StringCompare.compareUU       |  72  | avgt| 5  |15.078| ±	0.006|us/op
>> StringCompare.compareUU       |  80  | avgt| 5  |23.512| ±	0.011|us/op
>> StringCompare.compareUU       |  91  | avgt| 5  |24.284| ±	0.008|us/op
>> StringCompare.compareUU       |  101 | avgt| 5  |20.707| ±	0.017|us/op
>> StringCompare.compareUU       |  121 | avgt| 5  |29.302| ±	0.011|us/op
>> StringCompare.compareUU       |  181 | avgt| 5  |39.31	| ±	0.016|us/op
>> StringCompare.compareUU       |  256 | avgt| 5  |54.592| ±	0.392|us/op
>> StringCompare.compareUUWithLdp|  64  | avgt| 5  |16.389| ±	0.008|us/op
>> StringCompare.compareUUWithLdp|  72  | avgt| 5  |10.71 | ±	0.158|us/op
>> StringCompare.compareUUWithLdp|  80  | avgt| 5  |11.488| ±	0.024|us/op
>> StringCompare.compareUUWithLdp|  91  | avgt| 5  |13.412| ±	0.006|us/op
>> StringCompare.compareUUWithLdp|  101 | avgt| 5  |16.245| ±	0.434|us/op
>> StringCompare.compareUUWithLdp|  121 | avgt| 5  |16.597| ±	0.016|us/op
>> StringCompare.compareUUWithLdp|  181 | avgt| 5  |27.373| ±	0.017|us/op
>> StringCompare.compareUUWithLdp|  256 | avgt| 5  |41.74 | ±	3.5	 |us/op
>> 
>> From this table, we can see that in most cases, our patch is better than old one.
>> 
>> Thank you for your review. Any suggestions are welcome.
>
> Wang Huang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:
> 
>  - fix bugs
>  - Merge branch 'master' of https://gitee.com/ustc-wh/jdk into JDK-8268231
>  - fix style and add unalign test case
>  - refact codes
>  - draft of refactor
>  - 8268231: Aarch64: Use ldp in intrinsics for String.compareTo

Please provide the updated benchmark results for this version. Are you able to test it on several different machines?

src/hotspot/cpu/aarch64/stubGenerator_aarch64.cpp line 4892:

> 4890:           __ cmp(tmp1, tmp2);
> 4891:           __ ccmp(tmp1h, tmp2h, 0, Assembler::EQ);
> 4892:           __ br(__ NE, DIFF);

The line above uses `Assembler::EQ` for the condition code but this line uses `__ NE`. Better to be consistent and use `Assembler::` everywhere.

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PR: https://git.openjdk.java.net/jdk/pull/4722