RFR: 8252505: C1/C2 compiler support for blackholes [v19]

[Andrew Haley]

On Fri, 4 Dec 2020 12:42:32 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> I think testing is all-green in GH Actions. I also passed tier{1,2} locally. Also passes JMH validation tests. I think we are ready to integrate this. @theRealAph, @adinn, @cl4es, want to ack the current patch?

I'm testing on AArch64 now.

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PR: https://git.openjdk.java.net/jdk/pull/1203