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Reading the compiler's mind

The -XX:+LogCompilation flag produces a low-level XML file about compiler and runtime decisions, which may be interesting to some. The -XX:+UnlockDiagnosticVMOptions must come first. The dump is to hotspot.log in the current directory; use -XX:LogFile=foo.log to change this.

The format of this file is complex and subject to change. Here is an overview of the syntax, and a tool for parsing the files.

The XML file is also line-oriented, so simple greps or text editing scans are sometimes useful.