RFR: 8351640: Print reason for making method not entrant

[Vladimir Ivanov]

On Tue, 11 Mar 2025 11:36:59 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> A simple quality of life improvement. We are studying compiler dynamics in Leyden, and it would be convenient to know why the particular methods are marked as not entrant. We just need to pass the extra string argument to `nmethod::make_not_entrant` and print it out. 
> 
> Sample log excerpt for mainline:
> 
> 
> $ grep com.sun.tools.javac.util.IntHashTable::lookup print-compilation.log 
> 987   780       3       com.sun.tools.javac.util.IntHashTable::lookup (100 bytes)
> 1019  877       4       com.sun.tools.javac.util.IntHashTable::lookup (100 bytes)
> 1024  780       3       com.sun.tools.javac.util.IntHashTable::lookup (100 bytes)   made not entrant: not used
> 4995  877       4       com.sun.tools.javac.util.IntHashTable::lookup (100 bytes)   made not entrant: uncommon trap
> 5287 3734       3       com.sun.tools.javac.util.IntHashTable::lookup (100 bytes)
> 6615 5472       4       com.sun.tools.javac.util.IntHashTable::lookup (100 bytes)
> 6626 3734       3       com.sun.tools.javac.util.IntHashTable::lookup (100 bytes)   made not entrant: not used
> 
> 
> You can now clearly see the method lifecycle. 1 second in app lifetime, the method was initially compiled at level 3. Shortly after, it got compiled at level 4, turning level 3 method unused. 4 seconds later, level 4 method encountered uncommon trap, so we are back to level 3. After 1.3 seconds more, the final compilation at level 4 completed, and second level 3 compilation was removed as unused.
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `hotspot:tier1`
>  - [x] Linux x86_64 server fastdebug, `all`

src/hotspot/share/code/nmethod.cpp line 1965:

> 1963:   if (LogCompilation) {
> 1964:     if (xtty != nullptr) {
> 1965:       ttyLocker ttyl;  // keep the following output all in one block

Please, include same info in `LogCompilation` log.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23980#discussion_r1989937760