RFR: 8323497: On x64, use 32-bit immediate moves for narrow klass base if possible [v6]

[Thomas Stuefe]

On Thu, 22 May 2025 17:00:47 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> All right, I have more questions (unfortunately) :) See below.
> 
> Also, generic question. This handles decoding paths, should we also do this in `MacroAssembler::encode_klass*` and friends?

Yes, that seems worthwhile; I was surprised, I thought encode_klass is not used much. This increases gains to > 1% for tiers 1..3:


tier	        1	1	1	1
base	        3489120	3719112	8203576	3110424
decode	        3463976	3694000	8120336	3105840
Percent gain	0.72	0.68	1.01	0.15
decode+encode	3446864	3677008	8103328	3105848
Percent gain	1.21	1.13	1.22	0.15

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PR Comment: https://git.openjdk.org/jdk/pull/17340#issuecomment-2903621200