[Python-Dev] Expose stack effects to Python? (original) (raw)

Maciej Fijalkowski fijall at gmail.com
Wed Jul 3 14:22:32 CEST 2013

I wrote a thing that adds more structure to dis (but is not finished) https://bitbucket.org/pypy/pypy/src/15b0489c15d8150b22815312dd283aa5bafcdd67/lib_pypy/disassembler.py?at=default

On Wed, Jul 3, 2013 at 2:16 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:

On 3 July 2013 20:06, Victor Stinner <victor.stinner at gmail.com> wrote:

Hi, For my registervm project (fork of CPython using register-based bytecode, instead of stack-based bytecode), I implemented a Instruction.usestack() 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.usestack(): http://hg.python.org/sandbox/registervm/file/ff24dfecc27d/Lib/registervm.py#l546 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 opcodestackeffect() 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) * isterminal(): last instruction of a block * iscondjump(): 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. * isregused(), isregreplaced(), isregmodified(), 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 at gmail.com | Brisbane, Australia

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