RFR: 8288047: Accelerate Poly1305 on x86_64 using AVX512 instructions [v14]

[Volodymyr Paprotski]

On Fri, 11 Nov 2022 20:34:34 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> I am mystified at how it actually gets removed from the `assembler_x86.o` object on 32-bit.. The only reliable/portable way _would_ be with `#ifdef` but its not there.. so.. code-generation? `sed`-like preprocessing? Can one edit object files after the gcc ran? The build must be doing something clever!! Haven't seen it yet.. 
>> 
>> Whatever the trick is, `assembler_x86.hpp` gets it, but not `macroAssembler_x86.hpp`.
>> 
>> If it doesn't ring any bells, maybe I will spend some more time looking at the traces, maybe can figure out what the build script is doing to remove the symbol.
>
> It's not specific to `andq`: there's a huge `#ifdef` block around the definitions in `assembler_x86.hpp` (lines 12201 - 13773; and there's even a nested `#ifdef _LP64` (lines 13515-13585)!) , but declarations aren't guarded by `#ifdef _LP64`.

Yeah, just got to about the same conclusion by looking at the preprocessor `-E` output.. its declared in the header, but not defined in the 'cpp' file.. One would think that that's a compile error, but its been more then a decade since I looked at the C++ spec; 'C++ compiler is always right'.

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PR: https://git.openjdk.org/jdk/pull/10582