In VarHandles, we have more through Unsafe tests that are currently present in Hotspot. One of these tests asserts in LinearScan like this:

# Internal Error (/opt/jprt/T/P1/125327.sandoz/s/hotspot/src/share/vm/c1/c1_LinearScan.cpp:5597), pid=17455, tid=17463
# assert(false) failed: cannot spill interval that is used in first instruction (possible reason: no register found)

The problem seems to triggered on i586 only, not on x86_64. I have self-built several JDK 9 builds, and every build seems to fail; the oldest one I tried is jdk9-b80 -- others fail to compile with recent toolchains. Note that public JDK 9 EA builds, including 9b92 work fine, because asserts are stripped from there. It is unknown if the assert signifies a real trouble gone unnoticed in product bits. In product bits, LinearScan bails out, and skips C1 compile of the method:

 compilation bailout: LinearScan: no register found
    494 205 1 UnsafeTwoCASLong::testAccess (27 bytes) COMPILE SKIPPED: LinearScan: no register found (retry at different tier)

The minimized offending test:
 http://cr.openjdk.java.net/~shade/8143930/UnsafeTwoCASLong.java