RFR: 8273297: AES/GCM non-AVX512+VAES CPUs suffer after 8267125

[Andrew Haley]

On Tue, 7 Sep 2021 22:31:30 GMT, Smita Kamath <svkamath at openjdk.org> wrote:

> Performance dropped up to 10% for 1k data after 8267125 for CPUs that do not support the new intrinsic. Tests run were crypto.full.AESGCMBench and crypto.full.AESGCMByteBuffer from the jmh micro benchmarks.
> 
> The problem is each instance of GHASH allocates 96 extra longs for the AVX512+VAES intrinsic regardless if the intrinsic is used. This extra table space should be allocated differently so that non-supporting CPUs do not suffer this penalty. This issue also affects non-Intel CPUs too.

src/hotspot/share/opto/library_call.cpp line 6796:

> 6794: 
> 6795:   Node* avx512_subkeyHtbl = new_array(klass_node, intcon(96), 0);
> 6796:   if (avx512_subkeyHtbl == NULL) return false;

This looks very Intel-specific, but it's in generic code. Please make this constant 96 a symbol and push it into a header file in the x86 back end.

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PR: https://git.openjdk.java.net/jdk/pull/5402