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
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