On 6/9/06, Xiao-Feng Li <[EMAIL PROTECTED]> wrote:
Clever trick. But I don't understand why you want to create the Address object at all.
hmm... please read my example again. I do not create an Address object. And the call to invokespecial is nop'ed.
You can probably just invoke a method of Address to generate an Address object reference, and the method "invoke" bytecode can be identified by the JIT compiler easily and replaced by a nop or whatever proper. In this way, the Address object reference can be used directly as an "object reference", i.e., object pointer.
Well actually in what I propose, instances of Address are always an "int". Note that the JIT never has GC maps for ints. If I understand vmmagic correctly, instances of Address are only used for pointer arithmetic. They are never used as reference pointers. To use an Address as a reference pointer, you must convert it back to an ObjectReference.
Thanks, xiaofeng On 6/9/06, Weldon Washburn <[EMAIL PROTECTED]> wrote: > All, > > I am hoping someone who has worked on compilers can actually do the > JIT modifications. I don't have much experience in compilers. > > I am trying to get MMTk write barriers integrated into Harmony DRLVM. > I came up with the following scheme. I don't know if it is correct. > It would be great if someone from the MMTk crowd looked at it. If it > helps, I can also post this message on Jikes/MMTk mailing list. > > Build a shim between the DRLVM class loader and Jitrino.JET. The shim > would contain a lookup table that would map _local_ variables of > specific types to int. In particular, the shim would re-map local > variables of the below types to int: > > Address > Extent > Offset > Word > > The reason for the shim is to avoid modifying the class loader. This > should reduce the maintenance burden. > > Java source code that creates objects of the above classes is a now a > problem. For example, Java source code that does: > > int xx = 33; > Address a1 = new Address(xx); > > Translates to the following bytecode: > > bipush 33 > istore_1 > new //class Address > dup > iload_1 > invokespecial //Method "<init>": (I)V > astore_2 > > Basically the JIT needs to special case "new". If it is a new of > class Address/Extent/Offset/Word, substitute nop for the new bytecode. > If new has been substituted, then replace the following "dup" with a > nop. Leave iload_1 alone. Nop invokespecial. If the new was nop'ed, > replace astore_2 with istore_2. > > The bytecode sequence the JIT really sees is now: > > bipush 33 > istore_1 > nop //new //class Address > nop // dup > iload_1 > nop //invokespecial //Method "<init>": (I)V > istore_2 //astore_2 > > Another example: > > int xx = 33; > Address a1 = new Address(xx); > int kk = a1.toInt(); > > Translates to bytecode that looks like: > > > bipush 33 > istore_1 > new //class Address > dup > iload_1 > invokespecial //Method "<init>": (I)V > astore_2 > <<<<<<<<<<<<<<<<<<< new code starts here > aload_2 > invokevirtual //Method toInt(V)I > istore_3 > > All the bytecode down to astore_2 has already been described in the > first example. The additional bytecode would be magically remapped by > the JIT to: > > iload_2 // aload_2 > nop // invokevirtual //Method toInt(V)I > istore_3 > > Equivalent mappings will be needed for the rest of the methods of > class Address as well as Extent, Offset and Word. > > Will the above work? Thoughts? > > > > > -- > Weldon Washburn > Intel Middleware Products Division > > --------------------------------------------------------------------- > Terms of use : http://incubator.apache.org/harmony/mailing.html > To unsubscribe, e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] > > --------------------------------------------------------------------- Terms of use : http://incubator.apache.org/harmony/mailing.html To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
-- Weldon Washburn Intel Middleware Products Division --------------------------------------------------------------------- Terms of use : http://incubator.apache.org/harmony/mailing.html To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
