Re: [Python-Dev] Expose stack effects to Python?

I wrote a thing that adds more structure to dis (but is not finished) https://bitbucket.org/pypy/pypy/src/15b0489c15d8150b22815312dd283aa5bafcdd67... On Wed, Jul 3, 2013 at 2:16 PM, Nick Coghlan wrote:

On 3 July 2013 20:06, Victor Stinner wrote:

...

Hi,

For my registervm project (fork of CPython using register-based bytecode, instead of stack-based bytecode), I implemented a Instruction.use_stack() method which just checks if the stack is "used": read the stack, exchange values in the stack (like "ROT" instruction), push or pop a value.

Instruction.use_stack():

http://hg.python.org/sandbox/registervm/file/ff24dfecc27d/Lib/registervm.py#...

The method uses a dummy heuristic, just because it was quick to implement it, and it's enough for my use case.

To answer your question: yes, I would like a opcode_stack_effect() function.

registervm has its own disassembler which creates objects, rather than just generating a text representation of the bytecode. I'm using objects because I rewrite most instructions and I need more information and functions:

* disassembler (raw bytes => list of instructions) * assembler (list of instructions => raw bytes) * format an instruction (human readable assembler)

* is_terminal(): last instruction of a block * is_cond_jump(): the instruction is a conditional jump? hesitate to move this disassembler to CPython directly. I'm not sure that it would be useful, its API is maybe too specific to my registervm project. * is_reg_used(), is_reg_replaced(), is_reg_modified(), etc.: checks on registers * etc.

Would it be useful to have such high-level API in Python?

I finally committed a longstanding patch to add something like that a while ago for 3.4: http://docs.python.org/dev/library/dis#bytecode-analysis

It's still fairly low level, but already far more programmatically useful than the old disassembler text.

I'm still inclined to push higher level stuff out to external libraries - this patch was mostly about making some of our compiler tests a bit more maintainable, as well as giving third party libraries better building blocks without changing the dis module too much.

To get back to Larry's question, though, I think exposing the stack effects through dis.Instruction would be a good idea (since that will have access to the oparg to calculate the variable effects).

As far as how to expose the data to Python goes, I suggest adding an _opcode C module to back opcode.py and eliminate the manual duplication of the opcode values while you're at it.

Cheers, Nick.

-- Nick Coghlan | ncoghlan@gmail.com | Brisbane, Australia

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