RFR: 8357267: ZGC: Handle APX EGPRs spilling in ZRuntimeCallSpill

[Roberto Castañeda Lozano]

On Wed, 21 May 2025 12:33:26 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

> Patch has been verified using Intel SDE all test under test/hotspot/jtreg/compiler/gcbarriers are green.

Have you checked that these tests exercise `ZRuntimeCallSpill` significantly? Most tests in that directory seem to exercise C2's generated ZGC barriers, which use other spilling/restoring logic across runtime calls (`SaveLiveRegisters`). Also, I expect the register pressure in these test cases to be minimal, so it could be good to randomize register assignment to improve the testing effectiveness. Finally, `ZRuntimeCallSpill` is typically used in slow paths, which are rarely exercised in short-lived test cases. Have you considered altering the users of `ZRuntimeCallSpill` so that they are forced to always, or at least more often, enter the slow path, for testing purposes? [This PR](https://github.com/openjdk/jdk/pull/18967) did something similar in the context of C2 ZGC barriers.

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PR Comment: https://git.openjdk.org/jdk/pull/25351#issuecomment-2900619263