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:

> 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.

Thank you for your comment. I am looking at this pending PR again. I drafted it for now until I get a rfr version.

While I am implementing your suggestion, I found another typical optimization that is missing, which is pushing constant to right from `x + (con - y)` to `(x - y) + con`. I created a separate PR for it, https://github.com/openjdk/jdk/pull/7795. Can you take a look at that one if you get a chance? Thank you!

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