New UL log messages for the AOT cache are implemented using the "aot" tag. For example, in JDK-8350209: Preserve adapters in AOT cache, we are adding -Xlog:aot+codecache+init.

However, for historical reasons, many log message for the AOT cache use the "cds" tag. E.g.,

    java -XX:AOTCache=foo.aot -cp foo.jar -Xlog:cds,cds+module Foo

For a consistent user interface, we should make it possible for the user to get log messages about the AOT cache using -Xlog:aot. E.g.,

    java -XX:AOTCache=foo.aot -cp foo.jar -Xlog:aot,aot+module Foo

Some existing user scripts may rely on the "cds" logging output, so we should go through a deprecation process before we retire the "cds" log. For the time being, we should make "aot" as an alias of "cds".

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Specification:

- A LogTagSet is an ordered set of one or more LogTags

- In the JVM command line, a LogTagSet can be selected with one or more tags separated by the "+" sign. Examples

    cds
    cds+module
    cds+heap+mirror

- For a LogTagSet whose first tag is "cds", we allow the user to select this LogTagSet in the command-line by replacing the first tag with "aot. E.g.,

    aot
    aot+module
    aot+heap+mirror

- If the command-line contains no LogTagSets whose first tag is "cds", then all "cds" logs will be printed with a decoration that starts with "aot". E.g.,

$ java -Xlog:aot -Xlog:aot+codecache+init --version | head -2
[0.017s][info][aot] trying to map /jdk3/bld/tea-debug/images/jdk/lib/server/classes.jsa
[0.018s][info][aot,codecache,init] Initing CodeCache...

- However, for backwards compatibility, if the command-line contains at least one LogTagSets whose first tag is "cds", then we do not alter the decorations. I.e., the decorations will be printed exactly as written in the HotSpot C++ source code.

$ java -Xlog:cds -Xlog:aot+codecache+init --version | head -2
[0.017s][info][cds] trying to map /jdk3/bld/tea-debug/images/jdk/lib/server/classes.jsa
[0.018s][info][aot,codecache,init] Initing CodeCache...