RFR: 8335182: Consolidate and streamline String concat code shapes [v3]

[Claes Redestad]

On Tue, 9 Jul 2024 21:16:33 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> This PR attains a speed-up on some microbenchmarks by simplifying how we build up the MH combinator tree shape
>> (only use prependers with prefix, always add a suffix to the newArray combinator), then simplifying/inlining some of the code in the helper functions. 
>> 
>> Many simple concatenation expressions stay performance neutral, while the win comes from enabling C2 to better optimize more complex shapes (concat13String, concatMix4String, concatConst6String see relatively large improvements):
>> 
>> 
>> Name                                    Cnt     Base     Error      Test     Error  Unit  Change
>> StringConcat.concat13String              50   66.380 ±   0.189    53.017 ±   0.241 ns/op   1.25x (p = 0.000*)
>> StringConcat.concat4String               50   13.620 ±   0.053    12.382 ±   0.089 ns/op   1.10x (p = 0.000*)
>> StringConcat.concat6String               50   17.168 ±   0.070    16.046 ±   0.064 ns/op   1.07x (p = 0.000*)
>> StringConcat.concatConst2String          50    9.820 ±   0.081     8.158 ±   0.041 ns/op   1.20x (p = 0.000*)
>> StringConcat.concatConst4String          50   14.938 ±   0.124    12.800 ±   0.049 ns/op   1.17x (p = 0.000*)
>> StringConcat.concatConst6Object          50   56.115 ±   0.288    54.046 ±   0.214 ns/op   1.04x (p = 0.000*)
>> StringConcat.concatConst6String          50   19.032 ±   0.073    16.213 ±   0.093 ns/op   1.17x (p = 0.000*)
>> StringConcat.concatConstBoolByte         50    8.486 ±   0.066     8.556 ±   0.050 ns/op   0.99x (p = 0.004*)
>> StringConcat.concatConstInt              50    8.942 ±   0.052     7.677 ±   0.029 ns/op   1.16x (p = 0.000*)
>> StringConcat.concatConstIntConstInt      50   12.883 ±   0.070    12.431 ±   0.070 ns/op   1.04x (p = 0.000*)
>> StringConcat.concatConstString           50    7.523 ±   0.050     7.486 ±   0.044 ns/op   1.00x (p = 0.058 )
>> StringConcat.concatConstStringConstInt   50   11.961 ±   0.032    11.699 ±   0.049 ns/op   1.02x (p = 0.000*)
>> StringConcat.concatEmptyConstInt         50    7.778 ±   0.038     7.723 ±   0.037 ns/op   1.01x (p = 0.000*)
>> StringConcat.concatEmptyConstString      50    3.506 ±   0.026     3.505 ±   0.015 ns/op   1.00x (p = 0.930 )
>> StringConcat.concatEmptyLeft             50    3.573 ±   0.075     3.518 ±   0.057 ns/op   1.02x (p = 0.044 )
>> StringConcat.concatEmptyRight            50    3.713 ±   0.049     3.622 ±   0.053 ns/op   1.02x (p = 0.000*)
>> StringConcat.concatMethodConstString     50    7.418 ±   0.030     7.478 ±   0.066 ns/op   0.99x (p...
>
> Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Excess blankspace

Thanks for reviews and patience - went on vacation for a couple of weeks and didn't want to integrate this and leave any bug trail for others to deal with. Back part-time for a while so let's go!

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PR Comment: https://git.openjdk.org/jdk/pull/19927#issuecomment-2245022856