RFR: 8265938: C2's conditional move optimization does not handle top Phi

[Igor Ignatyev]

On Mon, 26 Apr 2021 06:46:55 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

> C2's CCP optimization sets the type of a PhiNode to TOP because it became dead after loop unrolling. Now since that node is not reachable from the bottom due to an infinite loop at the end of the method, CCP does not enqueue the PhiNode for IGVN. As a result, the dead subgraph is not removed. During loop opts, the conditional move optimization fails on the PhiNode because its type is top. The expected behavior is to simply bail out with "COMPILE SKIPPED: infinite loop (retry at different tier)".
> 
> I suggest to fix this by simply handling a TOP Phi in the conditional move optimization code.
> 
> This issue was reported by John Jiang (johnsjiang at tencent.com).
> 
> Thanks,
> Tobias

one way to solve it is to make the thread created at L#57 daemon thread (+L64: `thread.setDaemon(true);`).

I'd also recommend you to use `jdk.test.lib.Utils::adjustTimeout` to factor the sleep time at L66: `Thread.sleep(Utils.adjustTimeout(4000));`

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PR: https://git.openjdk.java.net/jdk/pull/3684