MonitorTransformer

A Transformer that rewrites synchronized blocks produced by older versions of the Java compiler (1.3 and older) into a more modern format. This is required for compatibility with Fernflower, which does not understand the older format.

This transformer depends on JSRInlinerAdapter.

It makes three changes:

• Inlines MONITOREXIT subroutines. JSRInlinerAdapter only replaces JSR/RET calls with GOTO. Fernflower needs the actual body of the subroutine to be inlined.

• Extends exception handler ranges to cover the MONITOREXIT instruction.

• Replaces ASTORE ALOAD MONITORENTER sequences with DUP MONITORENTER, which prevents Fernflower from emitting a redundant variable declaration.

There is one final difference that this transformer does not deal with: modern versions of the Java compiler add a second exception handler range to each synchronized block covering the MONITOREXIT sequence, with the handler pointing to the same MONITOREXIT sequence. Adding this isn't necessary for Fernflower compatibility.