RFR: 8353735: [JVMCI] Allow specifying storage kind of the callee save register

[Doug Simon]

On Fri, 4 Apr 2025 14:47:39 GMT, Yudi Zheng <yzheng at openjdk.org> wrote:

> Windows x64 ABI considers the upper portions of YMM0-YMM15 and ZMM0-ZMM15 volatile, that is, destroyed on function calls. This PR allows `RegisterConfig` implementations to refine the storage kind of callee save register, such that JVMCI compiler can exploit this information to avoid backing up full width of these registers.

Marked as reviewed by dnsimon (Reviewer).

src/jdk.internal.vm.ci/share/classes/jdk/vm/ci/code/RegisterConfig.java line 98:

> 96: 
> 97:     /**
> 98:      * Gets the storage kind for a callee save register.

I would add a second sentence describing the Window ABI example so that it's clear why this API exists.

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PR Review: https://git.openjdk.org/jdk/pull/24451#pullrequestreview-2747108590
PR Review Comment: https://git.openjdk.org/jdk/pull/24451#discussion_r2031411734