DISCLAIMER: These notes are from the defunct k8 project which precedes SquirrelJME. The notes for SquirrelJME start on 2016/02/26! The k8 project was effectively a Java SE 8 operating system and as such all of the notes are in the context of that scope. That project is no longer my goal as SquirrelJME is the spiritual successor to it.
03:51
I need information about both things, used registers and other register based allocations as required.
05:27
The one thing though is how exception handling would work, with registers going back and forth between the stack at various operations the stuff in the handlers would not be so stable. Some kind of analysis would be needed to prevent that. Say if the path of an exception depends on the state of a register before flow leaves the handler.
07:20
Actually exception handling in Java just has all of the stack variables get junked and instead only the locals remain. Due to that, some registers may never be set. So I need to perform flow control stuff on the decoded method to determine which registers are used when an exception handler is called. So I suppose the best thing to do is have local volatile registers which will never be permanent registers. Said stack based registers would consist of volatile ones. I can either do code analysis or have the method decoder write this information. Analysis of the code would be best as zones could be determined as needed. After decoding a reduction pass would remove pointless operations and jump targets that are never jumped to. Then other optimization passes would run as needed. After that before it is sent to the native recompiler there will be register volatility and zone checking. If a jump target is caused by an exception handler then any registers which are written to are replaced and do not count all. Then that information can be used to determine which registers should stick when an exception handler is called.
08:42
For some reason my branch target mapping is not working. And I just realized why as Operands extend AbstractList, which changes equals(). Since some of these operands have no registes, the result is null. So I need to change equals to just end up being a check against this rather than being a list.