[LLVMdev] "Bound Methods" in LLVM Bytecode

Evan Jones ejones at uwaterloo.ca
Fri Oct 28 13:34:58 PDT 2005


I have been thinking about efficient implementation of dynamically typed 
languages in my spare time. Specifically, I'm working on a toy 
implementation of a tiny piece of Python using LLVM as a native code 
generating JIT. I've run into a bit of an issue, involving how Python 
deals with method calls. I'm not sure how/if I can implement this in 
LLVM. In Python, the following code:

somefunc = a.method

Roughly translates into:

functionObject = lookup( "method" in object a )

The challenge is that if "method" is actually a method, calling it 
magically adds "a" as the first parameter. If it is NOT a method, then 
no messing with the arguments occurs. As far as can tell, this forces an 
implementation to create BoundMethod objects that wrap the actual method 
calls. The question is, how can I implement this efficiently, ideally 
using LLVM?

My idea is to add a NULL pointer as the first parameter to all function 
calls. "Normal" functions would ignore it, but methods would look at the 
first parameter to find the "this" pointer. I could then generate a tiny 
stub for each bound method that would do the following:

1. Replace the first argument with the appropriate "this"
2. Jump to the real function

Is it possible to do something like this in LLVM? Will it work if I just 
create a char array and copy in the appropriate native code for the 
current platform? I would rather let LLVM do the hard work, but if that 
isn't possible, I'm looking for some acceptable hack.

An additional ugly bit is that these objects will be created and 
destroyed frequently, so integration with LLVM's memory system is 
important. The last I checked, LLVM does not keep track of code in 
memory, so this would effectively create a memory leak.

Thanks for any help,

Evan Jones

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