RFR: 8334717: Add JVMCI support for APX EGPRs

[Doug Simon]

On Thu, 16 Jan 2025 16:01:32 GMT, Yudi Zheng <yzheng at openjdk.org> wrote:

> This PR marks extra general purpose registers introduced by Intel APX as Graal allocatables. It also drops AMD64/AArch64/RISCV64.flags and RegisterArray

src/jdk.internal.vm.ci/share/classes/jdk/vm/ci/code/RegisterAttributes.java line 58:

> 56:      *         element at index i holds the attributes of the register whose number is i.
> 57:      */
> 58:     public static RegisterAttributes[] createMap(RegisterConfig registerConfig, List<Register> registers) {

We should remove raw arrays as much as possible in JVMCI and replace them with immutable Lists:

     * @return an immutable list whose length is the max register number in {@code registers} plus 1. An
     *         element at index i holds the attributes of the register whose number is i.
     */
    public static List<RegisterAttributes[] createMap(RegisterConfig registerConfig, List<Register> registers) {

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PR Review Comment: https://git.openjdk.org/jdk/pull/23159#discussion_r2033171362