RFR: 8349563: Improve AbsNode::Value() for integer types

[Tobias Hotz]

On Wed, 19 Feb 2025 05:10:04 GMT, Jasmine Karthikeyan <jkarthikeyan at openjdk.org> wrote:

> Hi all,
> This is a small patch that improves the implementation of Value() for `AbsINode` and `AbsLNode` by returning the absolute value of the input range. Most of the logic is trivial except for the special case where `_lo == jint_min/jlong_min` which must return the entire type range when encountered, for which I've added a small proof in the comments. I've also added some unit tests and updated the file to limit IR check platforms with more granularity.
> 
> Thoughts and reviews would be appreciated!

test/hotspot/jtreg/compiler/c2/irTests/TestIRAbs.java line 295:

> 293:     public boolean testIntRange3(int in) {
> 294:         // [-9, -2] => [2, 9]
> 295:         return Math.abs(-((in & 7) + 2)) < 2;

Not sure if this is in scope for this PR, but `abs(x)` should be idealized into `0 - x` if x <= 0. This seems to be missing at the moment.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/23685#discussion_r1966721899