RFR: 8252505: C1/C2 compiler support for blackholes [v24]

[Aleksey Shipilev]

On Mon, 7 Dec 2020 10:48:04 GMT, Thomas Wuerthinger <github.com+5550412+thomaswue at openjdk.org> wrote:

> That could set a dangerous precedent as it is otherwise a strongly assumed global invariant that the executing Java code has identical semantics independent of whether it is compiled or interpreted. It is also the first intrinsic that is dynamically configurable from the command line.

As I said above, `BreakAt` already changes the semantics. Compiler commands is a low-level API to instruct compiler to do something special. Here, we want compiler to do something special. `blackhole` being treated as intrinsic in VM code is the implementation detail. The previous incarnations of the patch were not doing it, and it was only done to simplify the internal compiler hooks.
 
> Why did you dismiss the option to add a blackhole method to the JDK?

Because in my mind, public Java API does not carry its weight here, for a single-purpose use in JMH.

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