Lightning-AI/lightning-thunder

Support `torch.where(condition)` with thunder.jit

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#124 opened on Apr 3, 2024

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Description

🚀 Feature

Motivation

Mixtral uses it: https://github.com/mistralai/mistral-src/blob/8598cf582091a596671be31990448e0620017851/moe_one_file_ref.py#L215

Minimal Repro

import thunder

def fn(cond):
    return torch.where(cond)

thunder.jit(fn)(torch.randn(3) > 0)

Pitch

Support image from https://pytorch.org/docs/stable/generated/torch.where.html

Additional context

We already support torch.where(condition, input, other): https://github.com/search?q=repo%3ALightning-AI%2Flightning-thunder+%22def+where%22&type=code

cc @apaz-cli

Contributor guide

Research direction
Examine the existing implementation of `torch.where(condition, input, other)` in the thunder codebase and extend it to support the one argument variant `torch.where(condition)`, which returns indices of non zero elements.
Tech stack
pythonpytorch
Domain
backend
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
PythonPyTorch
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60