Reproducible with:

CONF=linux-x86-server-fastdebug make images run-test TEST=jdk/internal/math/FloatingDecimal/TestFloatingDecimal.java

2019-04-05 17:12:47,558] Agent[1]: stdout: 22062 DefinitionSpillCopy === _ 22050 [[ 25621 ]] vectorx[4]:{int}
[2019-04-05 17:12:47,558] Agent[1]: stdout: # To suppress the following error report, specify this argument
[2019-04-05 17:12:47,558] Agent[1]: stdout: # after -XX: or in .hotspotrc: SuppressErrorAt=/output.cpp:1404
[2019-04-05 17:12:47,558] Agent[1]: stdout: #
[2019-04-05 17:12:47,558] Agent[1]: stdout: # A fatal error has been detected by the Java Runtime Environment:
[2019-04-05 17:12:47,558] Agent[1]: stdout: #
[2019-04-05 17:12:47,558] Agent[1]: stdout: # Internal Error (/home/shade/trunks/jdk-jdk/src/hotspot/share/opto/output.cpp:1404), pid=1578, tid=1597
[2019-04-05 17:12:47,558] Agent[1]: stdout: # assert(false) failed: wrong size of mach node
[2019-04-05 17:12:47,558] Agent[1]: stdout: #
[2019-04-05 17:12:47,558] Agent[1]: stdout: # JRE version: OpenJDK Runtime Environment (13.0) (fastdebug build 13-internal+0-adhoc.shade.jdk-jdk)
[2019-04-05 17:12:47,558] Agent[1]: stdout: # Java VM: OpenJDK Server VM (fastdebug 13-internal+0-adhoc.shade.jdk-jdk, mixed mode, tiered, g1 gc, linux-x86)
[2019-04-05 17:12:47,559] Agent[1]: stdout: # Problematic frame:
[2019-04-05 17:12:47,560] Agent[1]: stdout: # V [libjvm.so+0x10eaf80] Compile::fill_buffer(CodeBuffer*, unsigned int*)+0xb20
[2019-04-05 17:12:47,560] Agent[1]: stdout: #

This reproduces on my i7-7820X, but not on TR 2950X. Passing -XX:UseAVX=2 makes the test pass. Must be AVX-512 related.