RFR: 8288047: Accelerate Poly1305 on x86_64 using AVX512 instructions [v16]

[Vladimir Ivanov]

On Tue, 15 Nov 2022 00:25:46 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> src/hotspot/cpu/x86/stubGenerator_x86_64_poly.cpp line 387:
>> 
>>> 385:   const Register t2 = r14;
>>> 386: 
>>> 387:   __ movq(a0, Address(limbs, 0));
>> 
>> I don't understand how it works. `limbs` comes directly from `c_rarg2` and contains raw oop. So, `Address(limbs, 0)` reads object mark word rather than the first element from the array. 
>> 
>> (Same situation in `poly1305_limbs_out`. And now I'm curious why doesn't object header corruption trigger a crash.)
>
> library_call.cpp takes care of that, it passes the address of 0'th element to the stub.

Ah, got it. Worth elaborating that in the comments. Otherwise, they confuse rather than help:

  // void processBlocks(byte[] input, int len, int[5] a, int[5] r)
  const Register input        = rdi; //input+offset
  const Register length       = rbx;
  const Register accumulator  = rcx;
  const Register R            = r8;

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