Lightning-AI / Lightning-AI/lightning-thunder

Add nvFuser support for thunder.torch.randn

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nvfuser nvidia
Dominant language
Python
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Description

## 🐛 Bug

```py
import thunder
import torch

@thunder.jit
def normal(shape, device):
return torch.randn(tuple(shape), device=device)

shape = [1, 4, 40, 84, 84]
t1 = normal(shape, device="cuda:0")
print(thunder.last_traces(normal)[-1]) # should have nvFusion0 there!
```
```py
def computation():
t6 = torch.randn((1, 4, 40, 84, 84), device=torch.device("cuda:0"), dtype=torch.float32) # t6: "cuda:0 f32[1, 4, 40, 84, 84]"
# t6 = ltorch.randn((1, 4, 40, 84, 84), generator=None, dtype=torch.float32, device=torch.device("cuda:0"), layout=torch.strided, requires_grad=False, pin_memory=False, out=None) # t6: "cuda:0 f32[1, 4, 40, 84, 84]"
# t6 = prims.randn((1, 4, 40, 84, 84), device=devices.Device("cuda:0"), dtype=dtypes.float32) # t6: "cuda:0 f32[1, 4, 40, 84, 84]"
return t6
```

cc @tfogal

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by running the provided thunder.jit example with the stated shape and CUDA device, then inspect the resulting trace from thunder.last_traces(normal)[-1]. Follow how torch.randn is lowered through the shown ltorch and prims forms and compare the trace with the expected nvFusion0 output. Done means the trace includes nvFuser for this reproducible case.

Written by the indexing model from the issue text.

Assessment

Tech stack
python, pytorch
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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