8308172: [Lilliput/JDK17] Revert disabling vzeroupper

[rkennke]

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.

---

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Issue

• JDK-8308172: [Lilliput/JDK17] Revert disabling vzeroupper

Reviewers

• Aleksey Shipilev (@shipilev - Reviewer)

Reviewing

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[bridgekeeper]

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[mlbridge]

Webrevs

• 00: Full (7519bcbf)

[shipilev]

Looks fine

[openjdk]

@rkennke This change now passes all automated pre-integration checks.

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After integration, the commit message for the final commit will be:

8308172: [Lilliput/JDK17] Revert disabling vzeroupper

Reviewed-by: shade

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[rkennke]

/integrate

[openjdk]

Going to push as commit a7a8efb.

[openjdk]

@rkennke Pushed as commit a7a8efb.

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