RFR: 8268858: Determine register pressure automatically by the number of available registers for allocation [v2]

[Vladimir Kozlov]

On Mon, 21 Jun 2021 18:52:03 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> Not for correctness.
>> The value was tested and verified in SPECjvm2008 by the author of LCM's register pressure scheduling.
>> Therefore I continue to use the original value.
>> “I did in fact experiment around with different values for both float and int pressure thresholds.  The versions in changelist work best for x64 and x86.” [1]
>> [1] http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2015-September/019005.html
>
> Okay, I got it. So originally for 64-bit FLOATPRESSURE was 14 (16 -2) and that is where `-2` came from.

But for avx512 it was 28 before and it is 30 now. I don't know which number is better for performance. But your change made difference.

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PR: https://git.openjdk.java.net/jdk/pull/4505