RFR: JDK-8300808: Accelerate Base64 on x86 for AVX2 [v15]

[Scott Gibbons]

On Tue, 14 Feb 2023 01:48:37 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> Scott Gibbons has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Add URL to microbenchmark
>
> src/hotspot/cpu/x86/stubGenerator_x86_64.cpp line 2399:
> 
>> 2397:      VM_Version::supports_avx512bw()) {
>> 2398:     __ cmpl(length, 31);     // 32-bytes is break-even for AVX-512
>> 2399:     __ jcc(Assembler::lessEqual, L_bruteForce);
> 
> The avx2 code needs the length to be atleast 0x2c (44) bytes. We could directly go to non-avx code instead of L_bruteForce here. We will save one subtract/branch.

Done.

> src/hotspot/cpu/x86/stubGenerator_x86_64.cpp line 2658:
> 
>> 2656:     // Check for buffer too small (for algorithm)
>> 2657:     __ subl(length, 0x2c);
>> 2658:     __ jcc(Assembler::lessEqual, L_tailProc);
> 
> This could be Assembler::less instead of Assembler::lessEqual.

Why?  There is no performance difference and the intent is clear.  Is this just a "style" thing?

> src/hotspot/cpu/x86/stubGenerator_x86_64.cpp line 2699:
> 
>> 2697:     __ addptr(dest, 0x18);
>> 2698:     __ subl(length, 0x20);
>> 2699:     __ jcc(Assembler::lessEqual, L_tailProc);
> 
> This could be Assembler::less instead of Assembler::lessEqual.

Why?  There is no performance difference and the intent is clear.  Is this just a "style" thing?

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PR: https://git.openjdk.org/jdk/pull/12126