RFR: 8363998: Implement Compressed Class Pointers for 32-bit [v3]

[Thomas Stuefe]

On Mon, 28 Jul 2025 16:18:12 GMT, Andrew Haley <aph at openjdk.org> wrote:

> Very nice! That's come out a lot cleaner than I was expecting.
> 
> Building and testing on a Raspberry Pi must have been fun. Not.

I did crossbuild on x64, so it was fast. Testing was not fun, though.

> src/hotspot/share/oops/compressedKlass.cpp line 56:
> 
>> 54:   // Klass pointers here, coding needs to be revised.
>> 55:   // We keep one page safety zone free to guard against size_t overflows on 32-bit. In practice
>> 56:   // this is irrelevant, since these upper address space parts are not user-addressable on
> 
> Suggestion:
> 
>   // this is irrelevant because these upper address space parts are not user-addressable on
> 
> Reason: correlation is not causation.

I did not know this distinction, had to look it up. Thanks!

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PR Comment: https://git.openjdk.org/jdk/pull/26491#issuecomment-3131022431
PR Review Comment: https://git.openjdk.org/jdk/pull/26491#discussion_r2238771664