15:34
Ok so, I still need to think of a better way to do this. One which is not insanely complex to write like SSA, but not insanely unoptimized like a purely naive approach. I also want it to be single pass for the most part if when possible. I think at best there would be two passes.
15:45
Ok, so a compiler is very complex to write. Well it can be easy but there are many considerations when writing them. Actually I have an idea. I can do register allocation at the start, which would be faster. But I can have alternative execution points in methods. Basically, I run through the entire method and I perform stack caching and register reallocation and such. However for backward jumps instead of having some kind of anti-aliasing barrier I can instead just generate extra machine code that does not have the given aspects of aliasing. So basically for points which are targets of jumps I have a copy of the state of variables and their alias state. If the variables are not compatible alias wise then an alternative chunk is executed. This means that I need basic blocks which are at the start of every jump target. This way, I will never need to juggle aliases and such. Since jumps are always to the start of a basic block I do not need to worry about inter instructions. Exceptions also only need to be checked after exceptional conditions also. But they still all need instancing to determine which exceptions get to be handled. I think one of the potentially slowest things would be instanceof checks.
16:02
There is this Stack Overflow response:
https://stackoverflow.com/questions/26335959/26337040#26337040
So basically, there is an index for each class which specifies the number of classes that are supertypes in the class. There is a list of superclasses for each class. If the source class has a depth greater than or equal to the target class then the cast may succeed. If it does then the depth of the target class (which is lower) is compared with the two table positions. If they refer to the same classes then the cast is OK. The only thing then are interfaces.
16:11
I could put this stuff in methods, but it would probably be best to check things.
16:12
Ok, so at this point the following must happen: The stack map table must be read in a type specifying matter and checked that way. In order to make the generated code much easier to work with, I need to know the actual types which are used everywhere.
16:14
Basically there is Object_variable_info which contains the type of an
Object.
16:17
Basically as execution continues, I need to know of all the types. This means
that for the index table of imports can also have static cast and instance
checks. It can only go in certain directions though. Basically for any type
which is known I can have a static check whether a given cast is always
invalid. So take for example there is an object of the type Double which is
verified. The programmer wants to cast it to Float. Basically there would
be a table entry which basically has a flag indicating if casting from
Double to Float is valid. When the byte code performs the check it will
see if the throw an exception flag is set. If it is then it will throw a cast
class exception or say the instanceof fails. But I can also have a flag for
a completely safe cast.
16:29
So if the cast is completely safe, it does not need to be checked. Otherwise it checks if it is not never safe, in which case it performs the expensive check. Then throws the exception or fails the instance.
16:32
So the code is basically:
if (A.isNotAnAlwaysSafeCastTo(B))
{
if (A.isAlwaysAFailingCastTo(B) || A.cannotBeCastedTo(B))
throw new ClassCastException(A + " -> " + B);
}
16:45
Also, I will need a check and flag for whether a given class is an interface or not. If a class is an interface then a more complex check is required for casting I believe.
16:53
So this actually makes things far easier. I just then need to layer this on top of the anti-aliasing code.
17:00
So essentially what I have are basic block queues with entry points. All blocks are pushed to a queue then compiled. Compilation is complete when all basic blocks have been compiled. I would potentially need natural control flow markers however to prevent potential falling into another block of code where it is not intended to flow into. So jump targets are important here along with the type information!
17:53
So I suppose what I need is a slight alternative to the cache and register states depending on the basic blocks. Since this is a new way to do things the old CacheStates system will not work at all. Something that manages the basic block queue and potential positions. Basically what I have is a chunk of byte code and I need a basic block queue with the aliasing information.
18:82
Actually to, a new JavaType could combine the normal types, objects, and
have native type imformation (pointer stuff). That way there is just a single
class instead of two. The class is going to become more complex due to the
fact that classes will be specified in it.