RFR: 8349452: Fix performance regression for Arrays.fill() with AVX512 [v2]

[Srinivas Vamsi Parasa]

On Fri, 21 Nov 2025 21:56:13 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> Srinivas Vamsi Parasa has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   undo size check for fill64_masked
>
> src/hotspot/cpu/x86/macroAssembler_x86.cpp line 9245:
> 
>> 9243: }
>> 9244: 
>> 9245: void MacroAssembler::fill32_unmasked(uint shift, Register dst, int disp, XMMRegister xmm,
> 
> This could be called as fill32_tail. Also good to replace overall fill32_masked with fill32_tail.

Please see this suggestion incorporated in the updated code.

> src/hotspot/cpu/x86/macroAssembler_x86.cpp line 9305:
> 
>> 9303: }
>> 9304: 
>> 9305: void MacroAssembler::fill64_unmasked(uint shift, Register dst, int disp,
> 
> This could be called as fill64_tail. Also good to replace overall fill64_masked with fill64_tail.

Please see this suggestion incorporated in the updated code.

> src/hotspot/cpu/x86/macroAssembler_x86.cpp line 9362:
> 
>> 9360:     jcc(Assembler::greater, L_fill_64_bytes);
>> 9361:     fill32_unmasked(shift, to, 0, xtmp, count, rtmp);
>> 9362:     jmp(L_exit);
> 
> Instead of repeating fill32_unmasked multiple time, you could jmp to say L_fill_32_tail and have the fill32_unmasked code there one time.

Please see this suggestion incorporated in the updated code.

> src/hotspot/cpu/x86/macroAssembler_x86.cpp line 9383:
> 
>> 9381:     fill64(to, 0, xtmp);
>> 9382:     subq(count, 64 >> shift);
>> 9383:     fill32_unmasked(shift, to, 64, xtmp, count, rtmp);
> 
> Instead of repeating fill64_unmasked multiple time, you could jmp to say L_fill_64_tail and have the fill64_unmasked code there one time.

Please see this suggestion incorporated in the updated code.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/28442#discussion_r2551288005
PR Review Comment: https://git.openjdk.org/jdk/pull/28442#discussion_r2551288279
PR Review Comment: https://git.openjdk.org/jdk/pull/28442#discussion_r2551289093
PR Review Comment: https://git.openjdk.org/jdk/pull/28442#discussion_r2551289710