RFR: 8351159: Remaining cleanups in cpu/x86 after 32-bit x86 removal [v2]

[Vladimir Kozlov]

On Tue, 28 Oct 2025 09:06:26 GMT, Anton Seoane Ampudia <aseoane at openjdk.org> wrote:

>> This PR carries out cleanup on the `cpu` and `os_cpu` directories after the removal of the 32-bit x86 architecture from HotSpot.
>> 
>> Mainly, code guarded by `IA32` or `X32`, or `!AMD64` or `!LP64` in a x86 context, has been removed. These guards are now redundant (e.g. checking for 64bit on a x86 context) or the code blocks never executed (e.g. code under `#ifdef X32`). Additionally, x86 AD files have been merged.
>> 
>> Please note that this changeset limits itself to changes under `cpu/x86` and `os_cpu/x86`. Other cleanups are filed under a different RFE, and consequently addressed in a different PR: [JDK-8351149](https://github.com/openjdk/jdk/pull/27990).
>> 
>> **Testing:** passes tiers 1-5
>
> Anton Seoane Ampudia has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Apply review comments

Main concern is merge of `.ad` files. One big file may be not optimal for JVM build as I remember. Please check JVM build time, especially `adlc` run time. If VM build times increased consider keeping files separate.

Note, `x86.ad` is mostly used for vector instructions definition. I suggest to rename it to `x64_vect.ad` and `x86_64.ad` to `x64.ad` if you keep files separate.

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PR Review: https://git.openjdk.org/jdk/pull/27987#pullrequestreview-3389775895