make test TEST=langtools/jdk/internal/shellsupport/doc/JavadocHelperTest.java TEST_VM_OPTS="-XX:+UseParallelGC"

on a fastdebug build fails reproducibly with

java.lang.OutOfMemoryError: Java heap space
at java.base/java.util.Arrays.copyOf(Arrays.java:3649)
at jdk.compiler/com.sun.tools.javac.parser.UnicodeReader.getRawCharacters(UnicodeReader.java:639)
at jdk.compiler/com.sun.tools.javac.parser.JavadocTokenizer.getLineMap(JavadocTokenizer.java:183)
at jdk.compiler/com.sun.tools.javac.parser.Scanner.getLineMap(Scanner.java:129)
at jdk.compiler/com.sun.tools.javac.parser.JavacParser.parseCompilationUnit(JavacParser.java:4023)
at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.parse(JavaCompiler.java:652)
at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.parse(JavaCompiler.java:629)
at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.parse(JavaCompiler.java:689)
at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.parseFiles(JavaCompiler.java:1043)
at jdk.compiler/com.sun.tools.javac.main.JavaCompiler$InitialFileParser.parse(JavaCompiler.java:1977)
at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.parseFiles(JavaCompiler.java:1030)
at jdk.compiler/com.sun.tools.javac.api.JavacTaskImpl.parseInternal(JavacTaskImpl.java:258)
at jdk.compiler/com.sun.tools.javac.api.JavacTaskImpl$$Lambda/0x00007f144b18bdb8.call(Unknown Source)
at jdk.compiler/com.sun.tools.javac.api.JavacTaskImpl.invocationHelper(JavacTaskImpl.java:152)
at jdk.compiler/com.sun.tools.javac.api.JavacTaskImpl.parse(JavacTaskImpl.java:248)
at jdk.compiler/jdk.internal.shellsupport.doc.JavadocHelper$OnDemandJavadocHelper.findSource(JavadocHelper.java:767)
at jdk.compiler/jdk.internal.shellsupport.doc.JavadocHelper$OnDemandJavadocHelper.getSourceElement(JavadocHelper.java:657)
at jdk.compiler/jdk.internal.shellsupport.doc.JavadocHelper$OnDemandJavadocHelper.getResolvedDocComment(JavadocHelper.java:170)
at JavadocHelperTest.testAllDocs(JavadocHelperTest.java:424)
at java.base/java.lang.invoke.LambdaForm$DMH/0x00007f144b030400.invokeVirtual(LambdaForm$DMH)
at java.base/java.lang.invoke.LambdaForm$MH/0x00007f144b038400.invoke(LambdaForm$MH)
at java.base/java.lang.invoke.Invokers$Holder.invokeExact_MT(Invokers$Holder)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invokeImpl(DirectMethodHandleAccessor.java:153)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
at java.base/java.lang.reflect.Method.invoke(Method.java:580)
at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:132)
at org.testng.internal.TestInvoker.invokeMethod(TestInvoker.java:599)
at org.testng.internal.TestInvoker.invokeTestMethod(TestInvoker.java:174)
at org.testng.internal.MethodRunner.runInSequence(MethodRunner.java:46)
at org.testng.internal.TestInvoker$MethodInvocationAgent.invoke(TestInvoker.java:822)
at org.testng.internal.TestInvoker.invokeTestMethods(TestInvoker.java:147)
at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:146)
java.lang.Exception: failures: 1
at com.sun.javatest.regtest.agent.TestNGRunner.main(TestNGRunner.java:104)
at com.sun.javatest.regtest.agent.TestNGRunner.main(TestNGRunner.java:58)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
at java.base/java.lang.reflect.Method.invoke(Method.java:580)
at com.sun.javatest.regtest.agent.MainWrapper$MainTask.run(MainWrapper.java:138)
at java.base/java.lang.Thread.run(Thread.java:1570)