RFR: 8305895: Implement JEP 450: Compact Object Headers (Experimental) [v42]

[Roman Kennke]

On Tue, 15 Oct 2024 22:31:27 GMT, Volodymyr Paprotski <duke at openjdk.org> wrote:

>> Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix aarch64.ad
>
> src/hotspot/cpu/x86/c2_stubGenerator_x86_64_string.cpp line 1634:
> 
>> 1632: 
>> 1633: 
>> 1634: // Copy the small (< 32 byte) haystack to the stack.  Allows for vector reads without page fault
> 
> Just to be pedantic, its `(<=32)` - this function also handles 32bytes case.
> 
> -  line 401: 
> 
>  __ cmpq(haystack_len, 0x20);
>  __ ja(L_bigSwitchTop);
> 
> - though line 293 (`highly_optimized_short_cases`) only seems to route16-byte cases here: 
> ```__ cmpq(haystack_len_p, isU ? 8 : 16);```

I am not sure what you are looking at, but line 293 reads:

__ cmpq(haystack_len_p, isU ? 16 : 32);


for me. IOW, it routes > 32 byte cases to `L_begin`. But the following cmp/ja also routes <= 32 byte cases there, when `needle_len > 6`.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/20677#discussion_r1802694667