RFR: JDK-8323497: On x64, use 32-bit immediate moves for narrow klass base if possible

[Aleksey Shipilev]

On Wed, 10 Jan 2024 15:01:18 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> @shipilev I like this. I'll wait for your patch to go in.
>
> I think it would be better to move to `movptr` here and start testing it. I suspect there are a few places in Hotspot where we count the actual instruction _size_ for some stuff, and even the `mov64` -> `movptr` rewrite without `movl` optimization would highlight it. I agree the final version should be tested when JDK-8323503 is in.

> FYI the logic for immediate matching is:

@merykitty, could you point me where that logic is? Cannot find it in current Hotspot sources, and would like to reference it in my PR.

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PR Review Comment: https://git.openjdk.org/jdk/pull/17340#discussion_r1447773214