RFR: 8281453: New optimization: convert `~x` into `-1-x` when `~x` is used in an arithmetic expression [v9]

[Quan Anh Mai]

On Thu, 15 Sep 2022 16:53:44 GMT, Zhiqiang Zang <duke at openjdk.org> wrote:

>> Similar to `(~x)+c` -> `(c-1)-x` and `~(x+c)` -> `(-c-1)-x` in #6858, we can also introduce similar optimizations for subtraction, `c-(~x)` -> `x+(c+1)` and `~(c-x)` -> `x+(-c-1)`.
>> 
>> To generalize, I convert `~x` into `-1-x` when `~x` is used in an arithmetic expression. For example, `c-(~x)` will be converted into `c-(-1-x)` which will match other pattern and will be transformed again in next iteration and finally become `x+(c+1)`.
>> 
>> The results of the microbenchmark are as follows:
>> 
>> Baseline:                                                                                                                                         
>> Benchmark                         Mode  Cnt  Score    Error  Units
>> NotOpTransformation.baselineInt   avgt   60  0.439 ±  0.001  ns/op
>> NotOpTransformation.baselineLong  avgt   60  0.439 ±  0.001  ns/op
>> NotOpTransformation.testInt1      avgt   60  0.603 ±  0.001  ns/op
>> NotOpTransformation.testInt2      avgt   60  0.603 ±  0.001  ns/op
>> NotOpTransformation.testLong1     avgt   60  0.658 ±  0.001  ns/op
>> NotOpTransformation.testLong2     avgt   60  0.658 ±  0.001  ns/op
>> 
>> Patch:
>> Benchmark                         Mode  Cnt  Score    Error  Units
>> NotOpTransformation.baselineInt   avgt   60  0.439 ±  0.001  ns/op
>> NotOpTransformation.baselineLong  avgt   60  0.439 ±  0.001  ns/op
>> NotOpTransformation.testInt1      avgt   60  0.329 ±  0.001  ns/op
>> NotOpTransformation.testInt2      avgt   60  0.329 ±  0.001  ns/op
>> NotOpTransformation.testLong1     avgt   60  0.329 ±  0.001  ns/op
>> NotOpTransformation.testLong2     avgt   60  0.329 ±  0.001  ns/op
>
> Zhiqiang Zang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   include microbenchmark.

Consider there are 2 statements:

    int x = ~a + b;
    int y = ~a | c;

Your transformation would duplicate the `~a` as it is transformed into `(-a - 1)` in the calculation of `x` but not in the calculation of `y`.

Thanks.

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PR: https://git.openjdk.org/jdk/pull/7376