RFR: 8281518: New optimization: convert "(x|y)-(x^y)" into "x&y"

[Quan Anh Mai]

On Wed, 9 Feb 2022 00:44:08 GMT, Zhiqiang Zang <duke at openjdk.java.net> wrote:

> Convert `(x|y)-(x^y)` into `x&y`, in `SubINode::Ideal` and `SubLNode::Ideal`.
> 
> The results of the microbenchmark are as follows:
> 
> Baseline:                                                                                                                                         
> Benchmark                                Mode  Cnt  Score   Error  Units
> SubIdeal_XOrY_Minus_XXorY_.baselineInt   avgt   60  0.481 ± 0.003  ns/op
> SubIdeal_XOrY_Minus_XXorY_.baselineLong  avgt   60  0.482 ± 0.004  ns/op
> SubIdeal_XOrY_Minus_XXorY_.testInt       avgt   60  0.901 ± 0.007  ns/op
> SubIdeal_XOrY_Minus_XXorY_.testLong      avgt   60  0.894 ± 0.004  ns/op
> 
> Patch:
> Benchmark                                Mode  Cnt  Score   Error  Units
> SubIdeal_XOrY_Minus_XXorY_.baselineInt   avgt   60  0.480 ± 0.003  ns/op
> SubIdeal_XOrY_Minus_XXorY_.baselineLong  avgt   60  0.483 ± 0.005  ns/op
> SubIdeal_XOrY_Minus_XXorY_.testInt       avgt   60  0.600 ± 0.004  ns/op
> SubIdeal_XOrY_Minus_XXorY_.testLong      avgt   60  0.602 ± 0.004  ns/op

There is a large number of transformations in this bitwise operation family such as `(x & y) | (x ^ y) == x | y`, `(x & y) ^ (x | y) == x ^ y`, `(x ^ y) ^ (x | y) == x & y` , etc and that does not even touch operations involving 3 operands. It seems both gcc and clang perform these 2-operand bitwise transformations so you could look at them to see if there is a more general way to achieve all combinations.
Thanks.

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PR: https://git.openjdk.java.net/jdk/pull/7395