RFR: 8277882: New subnode ideal optimization: converting "c0 - (x + c1)" into "(c0 - c1) - x" [v2]

[Dean Long]

On Mon, 29 Nov 2021 03:44:46 GMT, Zang, Zhiqiang <duke at openjdk.java.net> wrote:

>> Suggest two new optimizations that can be done in SubINode::Ideal.
>
> Zang, Zhiqiang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   clean.

Changes requested by dlong (Reviewer).

I think your tests need to check more cases, especially cases that use MIN_VALUE, MAX_VALUE, or otherwise cause underflow or overflow.

src/hotspot/share/opto/subnode.cpp line 197:

> 195:       jint c1 = phase->type(in2->in(2))->isa_int()->get_con();
> 196:       return new SubINode(phase->intcon(java_subtract(c0, c1)), in2->in(1));
> 197:   }

Should this code be checking for counted loops like below (see ok_to_convert)?

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PR: https://git.openjdk.java.net/jdk/pull/6441