I found this during work of JDK-8306088 / JDK-8304720.

With appended Test.java run like this:

./java -Xcomp -XX:CompileCommand=compileonly,Test::test -XX:+TraceLoopOpts -XX:+UseVectorCmov -XX:+UseCMoveUnconditionally -XX:+TraceSuperWord -XX:MaxVectorSize=32 -XX:+TraceNewVectors Test.java

I get:

# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/home/emanuel/Documents/fork7-jdk/open/src/hotspot/share/opto/node.hpp:392), pid=21814, tid=21831
# assert(i < _max) failed: oob: i=1, _max=1
#
# JRE version: Java(TM) SE Runtime Environment (21.0) (slowdebug build 21-internal-LTS-2023-04-17-1039212.emanuel...)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (slowdebug 21-internal-LTS-2023-04-17-1039212.emanuel..., compiled mode, tiered, compressed oops, compressed class ptrs, g1 gc, linux-amd64)
# Problematic frame:
# V [libjvm.so+0x416445] Node::in(unsigned int) const+0x41

Note: the body of the loop can contain the equals check, or non-equals - it fails for both:
dataFc[i] = (dataFa[i] == dataFb[i]) ? dataFa[i] : dataFb[i];
dataFc[i] = (dataFa[i] != dataFb[i]) ? dataFa[i] : dataFb[i];

My guess is that something is wrong with the "EQ/NEQ tests (cmpOpUCF2)" in x86.