How Can I Inspect the JIT-Compiled Assembly Code in the JVM?

Inspecting JIT-Compiled Code in JVM

The Java Virtual Machine (JVM) utilizes Just-In-Time (JIT) compilation to improve code execution efficiency. While the JIT operates seamlessly in the background, there may be instances when developers seek to examine the native code generated by the JIT. This article provides instructions on how to view the assembly code produced by the JIT.

General Usage

Run the JVM with the following options:

-XX:+UnlockDiagnosticVMOptions -XX:+PrintAssembly

Filter on a Specific Method

To isolate the assembly code for a specific method, use the following syntax:

-XX:+UnlockDiagnosticVMOptions -XX:CompileCommand=print,*MyClass.myMethod

Note that the method name might require quotes depending on the operating system. Inlined methods may not display all optimizations.

Installing Required Libraries on Windows

To access these options on Windows, it is necessary to install specific libraries. Prebuilt binaries can be obtained from the fcml project:

• hsdis-amd64.dll
• hsdis-i386.dll

Alternatively, the libraries can be built manually using Cygwin. Instructions for both methods are detailed in the guide from fmlc.

Additional Notes

• For Intel ASM syntax, use -XX:PrintAssemblyOptions=intel alongside other options.
• The output assembly code is typically verbose and may be challenging to interpret.
• Unlocking diagnostic VM options may impact performance. Use these options only when necessary for diagnostic purposes.

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