Re: writing two different bytecode parts at the same time

  If I understand you correctly, right now, the closest would be to use 
several MethodNode instances from the tree package (those implement 
MethodVisitor interface) and then use InsnLists from those instances to 
assemble them together and call insnList.accept(methodVisitor) after 
that to get the result.

  On the other hand I recall this is a common scenario for compilers 
(Janino and Kawa bytecode libs both have support for that). So we 
probably should add a new MethodWriter API to provide a more lightweight 
support, e.g. allow work with ByteVector trough MethodVisitor API. 
Perhaps add a method into the MethodWriter class like MethodVisitor 
branch(); which could record the current position and then would insert 
bytecodes emitted trough returned MethodVisitor right into that saved 
position. Eric, what do you say about that?

  regards,
  Eugene


Jochen Theodorou wrote:
> Hi all,
>
> I am currently experimenting in Groovy with a special way of compiling 
> expressions. One way is the classic way, the other is more or less 
> java style static compilation. Since I want to switch between them at 
> runtime and express it completely in bytecode I have currently a small 
> problem.
>
> So for example I would compile
>
> void foo(int x) {
>   x++
> }
>
> into something like this
>
> if !fastpath GOTO slowpath
>   ILAOD 1
>   IINC
>   ISTORE
> slowpath:
>   x' = box(x)
>   x' = x'.next()
>   x  = unbox(x)
>
> I hope you guys forgive me for using some shortcuts here, but it 
> should give away the idea
>
> Currently I can switch the compiler to do either the one thing or the 
> other, but I would like to do both at the same time. Ideally I would 
> like to do that with two method visitors on the same method. Then I 
> could do (not real API, I know):
>
> mv1.visitInsn(ILOAD, 1)
>
> mv2.visitInsn(ILOAD, 1)
> mv2.visitMethodcall(SBA.box(I)Object)
>
> to handle loading x in the fast path (mv1) and loading x in the slow 
> path (mv2). That means I can handle both ways while handling the x in 
> x++ and have not to duplicate the my AST, or revisit it.
>
> So basically I would like to be able to define a label and have one 
> method visitor write after it, while another one can write before it. 
> Or a way to somehow jump
>
> Is there anything slightly like that in th asm lib I can use?
>
> bye Jochen
>

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