RFR: 8281453: New optimization: convert "c-(~x)" into "x+(c+1)" and "~(c-x)" into "x+(-c-1)"

[Zhiqiang Zang]

On Wed, 9 Feb 2022 16:12:30 GMT, Quan Anh Mai <duke at openjdk.java.net> 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)`.
>> 
>> The results of the microbenchmark are as follows:
>> 
>> Baseline:                                                                                                                                         
>> Benchmark                        Mode  Cnt  Score   Error  Units
>> SubIdealCMinusNotX.baselineInt   avgt   60  0.504 ± 0.011  ns/op
>> SubIdealCMinusNotX.baselineLong  avgt   60  0.484 ± 0.004  ns/op
>> SubIdealCMinusNotX.testInt1      avgt   60  0.779 ± 0.004  ns/op
>> SubIdealCMinusNotX.testInt2      avgt   60  0.896 ± 0.004  ns/op
>> SubIdealCMinusNotX.testLong1     avgt   60  0.722 ± 0.004  ns/op
>> SubIdealCMinusNotX.testLong2     avgt   60  0.720 ± 0.005  ns/op
>> 
>> Patch:
>> Benchmark                        Mode  Cnt  Score   Error  Units
>> SubIdealCMinusNotX.baselineInt   avgt   60  0.487 ± 0.009  ns/op
>> SubIdealCMinusNotX.baselineLong  avgt   60  0.486 ± 0.009  ns/op
>> SubIdealCMinusNotX.testInt1      avgt   60  0.372 ± 0.010  ns/op
>> SubIdealCMinusNotX.testInt2      avgt   60  0.365 ± 0.003  ns/op
>> SubIdealCMinusNotX.testLong1     avgt   60  0.369 ± 0.004  ns/op
>> SubIdealCMinusNotX.testLong2     avgt   60  0.399 ± 0.016  ns/op
>
> Since `~x == -1 - x` and these 2 operations' costs are essentially the same. It would be much easier if you just check whether the not result is used in an arithmetic operation and transform the former to the latter. The reverse is also true, if you find a `-1 - x` being fed into a bitwise just transform it to a `~x` then.
> Thanks.

Hello @merykitty I finished converting `~x` to `-1-x` when it appears in any add or sub nodes, as you suggested; so now it can really support a wide list of transformation: `c-(~x) => x + (c+1)`, `~x - ~y => y - x`, `(x+1) + ~y => x - y`, etc, which are all created as new tests. Can you help review again thank you.

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PR: https://git.openjdk.java.net/jdk/pull/7376