Compiler optimization: Java bytecode

Question

I'm currently writing a toy compiler targeting Java bytecode in the translation.

I would like to know if there is some kind of catalog, maybe a summary, of various simple peephole optimizations that can be made in the emitted bytecode before writing the .class file. I actually am aware of some libraries that have this functionality, but I'd like to implement that myself.

Answer 1

You are aware of Proguard? http://proguard.sourceforge.net/

This is a great bytecode optimizer which implements a lot of optimizations. See the FAQ for a list: http://proguard.sourceforge.net/FAQ.html

• Evaluate constant expressions.
• Remove unnecessary field accesses and method calls.
• Remove unnecessary branches.
• Remove unnecessary comparisons and instanceof tests.
• Remove unused code blocks.
• Merge identical code blocks.
• Reduce variable allocation.
• Remove write-only fields and unused method parameters.
• Inline constant fields, method parameters, and return values.
• Inline methods that are short or only called once.
• Simplify tail recursion calls.
• Merge classes and interfaces.
• Make methods private, static, and final when possible.
• Make classes static and final when possible.
• Replace interfaces that have single implementations.
• Perform over 200 peephole optimizations, like replacing ...*2 by ...<<1.
• Optionally remove logging code.

I'm sure you can further look into the source code to understand how they are implemented.