Following 6 tests failed in 9-jigsaw nightly testing:
java/lang/String/concat/ImplicitStringConcat.java
java/lang/String/concat/ImplicitStringConcatArgCount.java
java/lang/String/concat/ImplicitStringConcatBoundaries.java
java/lang/String/concat/ImplicitStringConcatMany.java
java/lang/String/concat/ImplicitStringConcatManyLongs.java
java/lang/String/concat/ImplicitStringConcatShapes.java

Tests failed on all platforms (Lin, Mac, Sol, Win), with similar error message, e.g.:

java.lang.reflect.InvocationTargetException
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(java.base@9-ea/DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(java.base@9-ea/Method.java:531)
at com.sun.javatest.regtest.agent.RegressionCompileCommand.run(RegressionCompileCommand.java:248)
at com.sun.javatest.regtest.agent.CompileActionHelper.runCompile(CompileActionHelper.java:92)
at com.sun.javatest.regtest.agent.AgentServer.doCompile(AgentServer.java:208)
at com.sun.javatest.regtest.agent.AgentServer.run(AgentServer.java:179)
at com.sun.javatest.regtest.agent.AgentServer.main(AgentServer.java:59)
Caused by: java.lang.AssertionError: StringConcatFactory-based string concat is requested on a platform that does not support it.
at com.sun.tools.javac.util.Assert.error(jdk.compiler@9-ea/Assert.java:162)
at com.sun.tools.javac.jvm.StringConcat.makeConcat(jdk.compiler@9-ea/StringConcat.java:89)
at com.sun.tools.javac.jvm.StringConcat.instance(jdk.compiler@9-ea/StringConcat.java:75)
at com.sun.tools.javac.jvm.Gen.<init>(jdk.compiler@9-ea/Gen.java:105)
at com.sun.tools.javac.jvm.Gen.instance(jdk.compiler@9-ea/Gen.java:86)
at com.sun.tools.javac.main.JavaCompiler.<init>(jdk.compiler@9-ea/JavaCompiler.java:392)
at com.sun.tools.javac.main.JavaCompiler.instance(jdk.compiler@9-ea/JavaCompiler.java:101)
at com.sun.tools.javac.main.Main.compile(jdk.compiler@9-ea/Main.java:246)
at com.sun.tools.javac.main.Main.compile(jdk.compiler@9-ea/Main.java:143)
at com.sun.tools.javac.Main.compile(jdk.compiler@9-ea/Main.java:73)
... 8 more
result: Error. Error invoking compiler