RFR: 8333893: Optimization for StringBuilder append boolean & null [v4]

[Emanuel Peter]

On Tue, 11 Jun 2024 11:35:28 GMT, Shaojin Wen <duke at openjdk.org> wrote:

>> After PR https://github.com/openjdk/jdk/pull/16245, C2 optimizes stores into primitive arrays by combining values ​​into larger stores.
>> 
>> This PR rewrites the code of appendNull and append(boolean) methods so that these two methods can be optimized by C2.
>
> Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   revert

Ah, another issue is method inlining. It seems that in 1.2, the method is not inlined:
` 103  StoreB  === 88 78 101 80  [[ 18 ]]  @byte[int:>=0] (java/lang/Cloneable,java/io/Serializable):exact+any *, idx=5;  Memory: @byte[int:>=0] (java/lang/Cloneable,java/io/Serializable):NotNull:exact+any *, idx=5; !jvms: StringUTF16::putChar @ bci:52 (line 72)`
In the extra information I only see `StringUTF16::putChar @ bci:52 (line 72)`, so this method was not inlined. So of course there are only the 2 stores to be merged from `putChar`. Maybe you can do something about this with `@ForceInline`. 

In 2.2 I see there is more inlining:
`  865  StoreB  === 656 839 863 45  [[ 885 ]]  @byte[int:>=0] (java/lang/Cloneable,java/io/Serializable):exact+any *, idx=10;  Memory: @byte[int:>=0] (java/lang/Cloneable,java/io/Serializable):NotNull:exact+any *, idx=10; !jvms: StringUTF16::putChar0 @ bci:19 (line 1587) StringUTF16::putCharsAt @ bci:34 (line 1572) AbstractStringBuilder::appendNull @ bci:63 (line 647) AbstractStringBuilder::append @ bci:5 (line 587) StringBuilder::append @ bci:2 (line 179)`
Though I cannot seem to map it to your java code, maybe you pasted things together wrongly here.

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PR Comment: https://git.openjdk.org/jdk/pull/19626#issuecomment-2162118831