SquirrelJME/SquirrelJME

# 2015/03/11

***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.