[8] Heads-up: LRB strength selector needs to consider MemBar nodes?

[Aleksey Shipilev]

This happens in sh/jdk8 only. But it might indicate we need to consider MemBar nodes in the
ShenandoahLoadReferenceBarrierNode::get_barrier_strength in all releases?

$ build/linux-x86_64-normal-server-slowdebug/images/j2sdk-image/bin/java
-XX:+UnlockExperimentalVMOptions -XX:+UseShenandoahGC -jar ~/Downloads/renaissance-mit-0.9.0.jar
akka-uct -r 5
====== akka-uct (actors), iteration 0 started ======
Unknown node in get_barrier_strength:
 2141	ShenandoahLoadReferenceBarrier	=== _  2142  [[ 2135  2140  2211 ]]
Oop:scala/concurrent/forkjoin/ForkJoinTask * !orig=284 !jvms: ForkJoinPool::scan @ bci:162
 2208	Proj	===  2209  [[ 2143  2211 ]] #2  Memory: @BotPTR *+bot, idx=Bot; !orig=280 !jvms:
ForkJoinPool::scan @ bci:162
 2255	Proj	===  2209  [[ 2143  2211 ]] #0 !orig=279 !jvms: ForkJoinPool::scan @ bci:162
 2211	MemBarAcquire	===  2255  1  2208  1  1  2141  [[ 2210  2254 ]]  !orig=285 !jvms:
ForkJoinPool::scan @ bci:162
# To suppress the following error report, specify this argument
# after -XX: or in .hotspotrc:  SuppressErrorAt=/shenandoahSupport.cpp:2969
#
# A fatal error has been detected by the Java Runtime Environment:
#
#  Internal Error
(/home/shade/trunks/shenandoah-jdk8/hotspot/src/share/vm/gc_implementation/shenandoah/shenandoahSupport.cpp:2969),
pid=31711, tid=0x00007fd69a4ab700
#  Error: ShouldNotReachHere()
#
# JRE version: OpenJDK Runtime Environment (8.0) (build 1.8.0-internal-debug-shade_2019_10_25_11_54-b00)
# Java VM: OpenJDK 64-Bit Server VM (25.71-b00-debug mixed mode linux-amd64 compressed oops)
# Failed to write core dump. Core dumps have been disabled. To enable core dumping, try "ulimit -c
unlimited" before starting Java again
#
# An error report file with more information is saved as:
# /home/shade/trunks/shenandoah-jdk8/hs_err_pid31711.log
#
# Compiler replay data is saved as:
# /home/shade/trunks/shenandoah-jdk8/replay_pid31711.log
#
# If you would like to submit a bug report, please visit:
#   http://bugreport.java.com/bugreport/crash.jsp
#
Current thread is 140559688316672
Dumping core ...
Aborted (core dumped)

-- 
Thanks,
-Aleksey