[lilliput-jdk17u:lilliput] RFR: 8308172: [Lilliput/JDK17] Revert disabling vzeroupper

[Aleksey Shipilev]

On Tue, 16 May 2023 10:57:52 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

> While looking through the diff between Lilliput/JDK17 and upstream JDK17, I noticed one change in library_call.cpp that should not be there, it probably slipped through from debugging.
> 
>         void clear_upper_avx() {
>       #ifdef X86
>     -     if (UseAVX >= 2) {
>     +     if (false && UseAVX >= 2) {
>             C->set_clear_upper_avx(true);
>           }
>       #endif
>         }
>  
> This prevents emitting vzeroupper instructions on x86_64. I believe this will have performance impact when transitioning between AVX and SSE code. We should revert this.

Looks fine

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Marked as reviewed by shade (Reviewer).

PR Review: https://git.openjdk.org/lilliput-jdk17u/pull/18#pullrequestreview-1428390413