We're missing a read-barrier in a C1 intrinsic for NIO checkIndex. This is the root cause for: http://mail.openjdk.java.net/pipermail/shenandoah-dev/2017-December/004495.html This is the fix: http://cr.openjdk.java.net/~rkennke/c1-missing-barrier/webrev.00/ Ok? Roman