RFR: 8327380: Add tests for Shenandoah barrier expansion optimization

[Aleksey Shipilev]

On Wed, 17 Apr 2024 13:27:11 GMT, Kangcheng Xu <kxu at openjdk.org> wrote:

> The Ideal graph for Shenandoah barrier expansion is optimized so that unnecessary checks are eliminated; however, currently there is no test cases to determine these optimizations are in effect.
> 
> Adding unit tests with the IR test framework will support related code changes in the future.

Marked as reviewed by shade (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/18814#pullrequestreview-2136465483