RFR: 8217230: assert(t == t_no_spec) failure in NodeHash::check_no_speculative_types()

[Yangfei (Felix)]

Hi,

Original bug:
    https://bugs.openjdk.java.net/browse/JDK-8217230 
    https://hg.openjdk.java.net/jdk-updates/jdk11u/rev/a5a3822a7239 

JDK-8217230 is a regression by JDK-8214862 (https://bugs.openjdk.java.net/browse/JDK-8214862).
JDK-8214862 was backported to openjdk8u272, but JDK-8217230 is not there.

This bug was triggered only once for this test case in my local jtreg run (hard to reproduce): 
    java/util/concurrent/ConcurrentQueues/RemovePollRace.java

Patch does not apply to 8u cleanly due to changes in surrounding context in file compile.hpp.
8u webrev:
    http://cr.openjdk.java.net/~fyang/8217230-8u/webrev.00 

The fix is simple and should be low risk (it removes a dead node from the C2 IR).
Performed full jtreg test with fastdebug build on x86_64 Linux.
OK to backport?

Thanks,
Felix