RFR: 8256718: Obsolete the long term deprecated and aliased Trace flags

[Coleen Phillimore]

On Mon, 30 Nov 2020 21:13:05 GMT, Harold Seigel <hseigel at openjdk.org> wrote:

> Please review this change to obsolete the deprecated and aliased Trace flags.  The now empty aliased_logging_flags support was left in arguments.cpp for use by trace flags that get deprecated and aliased in the future.
> 
> With this change, users will get the following example messages when using these obsolete flags, depending on whether -XX:+... or -XX:-... was specified:
> 
> VM warning: Ignoring option TraceClassPaths; support was removed in 16.0.  Please use -Xlog:class+path=info instead.
> 
> VM warning: Ignoring option TraceClassPaths; support was removed in 16.0.  Please use -Xlog:class+path=off instead.
> 
> The change was tested with tiers1and 2 on Linux, Windows, and MacOS, and tiers 3-5 on Linux x64 and with JCK lang and vm tests.
> 
> Thanks, Harold

I agree with David.  We should remove the helpful messages at least for most of the obsolete Print/Trace flags.  Not sure about the big 3 though.

src/hotspot/share/runtime/arguments.cpp line 617:

> 615: #ifndef PRODUCT
> 616: // These options are removed in jdk9. Remove this code for jdk10.
> 617: static AliasedFlag const removed_develop_logging_flags[] = {

I think this removed_develop_logging_flags infrastructure should be removed.

src/hotspot/share/runtime/arguments.cpp line 612:

> 610:   { "TraceRedefineClasses",      "-Xlog:redefine+class=",      "info",  "16.0" },
> 611:   { "PrintJNIResolving",         "-Xlog:jni+resolve=",         "debug", "16.0" },
> 612:   { NULL, NULL, NULL, NULL }

I think if we wanted to give a message that the flag was obsolete and to suggest changing the command line, we should only do it for -XX:+TraceClassLoading and -XX:+TraceExceptions (I'd originally thought -XX:+TraceClassUnloading was important enough to release note but now I'm not so sure.)   The rest of the flags should either go in the table that they're no longer recognized.

src/hotspot/share/runtime/arguments.cpp line 1325:

> 1323:               *arg == '+' ? obs_replacement->tag_name : "off");
> 1324:       return true;
> 1325:     }

I see you left this empty in case we change more flags to logging flags.  I don't see any Trace flags left that users would care about that merit this amount of helpfulness.  I think this should be removed too.

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Changes requested by coleenp (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/1525