LoadNode::find_previous_arraycopy fails with "broken allocation" assert

We get a hotspot assertion error running http client tests using new TLS1.3 implementation in jdk/jdk on Mach5. Looks like it might be C2 intrinsics related (MacOSX only).

A Mach 5 job today showing the problem is at [1]. The three failures are all the same cause. In this run, the problem is seen on macos releases Yosemite and High Sierra.

We cannot reliably reproduce it outside Mach 5. To reproduce (in m5), start with current jdk/jdk forest, and add the patch attached to this report (which enables use of TLS1.3) to open. Then submit mach 5 job with:

mach5 remote-build-and-test -b macosx-x64-debug --test open/test/jdk/java/net/httpclient --email xxx@oracle.com --test-repeat 50

# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/scratch/mesos/slaves/c4ee7e63-1ded-4e8c-9581-ce26f27e3af4-S221801/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/844482a8-c3dc-4753-b437-e742c427a048/runs/20999157-2932-4ce1-817e-87734d38d1e3/workspace/open/src/hotspot/share/opto/memnode.cpp:521), pid=98920, tid=23555
# assert(alloc != __null && (!ReduceBulkZeroing || alloc->initialization()->is_complete_with_arraycopy())) failed: broken allocation
#
# JRE version: Java(TM) SE Runtime Environment (11.0) (fastdebug build 11-internal+0-2018-06-27-1550285.michael.x.mcmahon.jdk)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (fastdebug 11-internal+0-2018-06-27-1550285.michael.x.mcmahon.jdk, mixed mode, tiered, compressed oops, g1 gc, bsd-amd64)
# No core dump will be written. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
#