RFR: 8320206: Some intrinsics/stubs missing vzeroupper on x86_64

[Vladimir Kozlov]

On Wed, 15 Nov 2023 21:28:46 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

> The following intrinsics/stubs are missing vzeroupper:
> adler32 (since JDK17)
> count_positives (since JDK 9)
> chacha20 (since JDK 20)
> string indexOfChar (since JDK 9)
> 
> Adding the missing vzeroupper to avoid AVX-SSE transition penalties.

I understand that originally it was good decision to generate vzeroupper in all places where we use avx512 wide instructions (C2 generated SSE instructions at that time). May be it is time to check if C2 still generate SSE now.  If not we should fix it so that we can remove  vzeroupper in intrinsic stubs used by C2 only.

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PR Comment: https://git.openjdk.org/jdk/pull/16678#issuecomment-1815671083