My colleague Ron Shapiro reports that in a large real-world compilation FileManager#list spent ~500ms allocating EnumSets at these sites:

http://hg.openjdk.java.net/jdk/jdk/file/02e648ae46c3/src/jdk.compiler/share/classes/com/sun/tools/javac/file/JavacFileManager.java#l520

http://hg.openjdk.java.net/jdk/jdk/file/02e648ae46c3/src/jdk.compiler/share/classes/com/sun/tools/javac/file/JavacFileManager.java#l520

Extracting the enums to a constant (the same approach used for sourceOrClass earlier in that class [1]) is a modest performance improvement.

[1] http://hg.openjdk.java.net/jdk/jdk/file/02e648ae46c3/src/jdk.compiler/share/classes/com/sun/tools/javac/file/JavacFileManager.java#l107