RFR: 8283094: Add Ideal transformation: x + (con - y) -> (x - y) + con

[Quan Anh Mai]

On Fri, 11 Mar 2022 23:40:19 GMT, Zhiqiang Zang <duke at openjdk.java.net> wrote:

> Hello,
> 
> `x + (con - y)  -> (x - y) + con` is a widely seen pattern; however it is missing in current implementation, which prevents some obvious constant folding from happening, such as `x + (1 - y) + 2` will be not optimized at all, rather than into `x - y + 3`.
> 
> This pull request adds this transformation.

src/hotspot/share/opto/addnode.cpp line 317:

> 315:   }
> 316: 
> 317:   // Convert (con - y) + x into "(x - y) + con"

This is the generalisation of the above transformations, you could consider removing them.

test/hotspot/jtreg/compiler/c2/irTests/TestIRAddIdealXPlus_ConMinusY_.java line 36:

> 34:  * @run driver compiler.c2.irTests.TestIRAddIdealXPlus_ConMinusY_
> 35:  */
> 36: public class TestIRAddIdealXPlus_ConMinusY_ {

Could you consider putting this in [SubINodeIdealizationTests](https://github.com/openjdk/jdk/blob/d24b6754a216c6d8b4d2fd1154dcf62d9e2c6c46/test/hotspot/jtreg/compiler/c2/irTests/SubINodeIdealizationTests.java) instead. Also I think it would be preferrable to have another PR to move the likes of [TestSpecialCasesOf_AMinusB_Plus_CMinusD_InAddIdeal](https://github.com/openjdk/jdk/blob/d24b6754a216c6d8b4d2fd1154dcf62d9e2c6c46/test/hotspot/jtreg/compiler/c2/irTests/TestSpecialCasesOf_AMinusB_Plus_CMinusD_InAddIdeal.java) to the corresponding group. Thanks.

-------------

PR: https://git.openjdk.java.net/jdk/pull/7795