[lworld] RFR: 8255541: [lworld] Improve array layout checks in C2 compiled code

[Sergey Kuksenko]

On Wed, 28 Oct 2020 13:56:51 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

> C2 should use a single bit test of the layout helper value to check for flat/null-free inline type arrays. This is a prerequisite of JDK-8255046 which will then add support for checking the corresponding bits in the mark word instead.
> 
> Best regards,
> Tobias

Sorry, I didn't have time to make a full perf review of this patch yet.
But anyway, here are preliminary performance results, for "aaload" operation:
if take time (than smaller than better) of aaload as 100 - baseline (-XX:-EnableValhalla) then:
-XX:+EnableValhalla -XX:+UseCompressedOops: before the PR - 126, after the PR - 110
-XX:+EnableValhalla -XX:-UseCompressedOops: before the PR - 108, after the PR - 107
I'd rather say that this PR are very nice for performance point of view.
More detailed analysis is in progress.

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PR: https://git.openjdk.java.net/valhalla/pull/244