Lightning-AI / Lightning-AI/lightning-thunder

Proxy renaming in general jit sometimes is skipped

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jit thunderfx
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Description

## 🐛 Bug

Proxy renaming in the initial trace doesn't work sometimes. Let's check how does the initial trace look like for the following example (taken from test_core.py::test_cse):
```py
import thunder
import torch

from thunder import clang

def func(x, y, device):
a = x * y
b = y / x
c = x * y
d = y / x
z = a * b
w = c * d
m = w * 1
a = clang.uniform(w.shape, device=device, dtype=thunder.float16)
return z, w, m, a

x = torch.randn(3, 4, device='cuda:0')
y = torch.randn(3, 4, device='cuda:0')
trace = thunder.trace()(func, x, y, 'cuda:0')
print(trace)
func = trace.python_callable()
jfunc = thunder.jit(func, executors=["torch"])
out = jfunc(x, y, device='cuda:0')
print(thunder.last_traces(jfunc)[0])
```
The initial trace in thunder.jit is
```py
def computation(x, y):
# x: "cuda:0 f32[3, 4]"
# y: "cuda:0 f32[3, 4]"

# thunder.func_39:15: t0 = ltorch.mul(x, y) # t0: "cuda:0 f32[3, 4]"
t0 = ltorch.mul(x, y) # t0: "cuda:0 f32[3, 4]"
# t0 = prims.mul(x, y) # t0: "cuda:0 f32[3, 4]"

# thunder.func_39:16: t1 = ltorch.true_divide(y, x) # t1: "cuda:0 f32[3, 4]"
t1 = ltorch.true_divide(y, x) # t1: "cuda:0 f32[3, 4]"
# t1 = prims.div(y, x) # t1: "cuda:0 f32[3, 4]"

# thunder.func_39:17: t2 = ltorch.mul(x, y) # t2: "cuda:0 f32[3, 4]"
t2 = ltorch.mul(x, y) # t2: "cuda:0 f32[3, 4]"
# t2 = prims.mul(x, y) # t2: "cuda:0 f32[3, 4]"

# thunder.func_39:18: t3 = ltorch.true_divide(y, x) # t3: "cuda:0 f32[3, 4]"
t3 = ltorch.true_divide(y, x) # t3: "cuda:0 f32[3, 4]"
# t3 = prims.div(y, x) # t3: "cuda:0 f32[3, 4]"

# thunder.func_39:19: t4 = ltorch.mul(t0, t1) # t4: "cuda:0 f32[3, 4]"
t4 = ltorch.mul(t0, t1) # t4: "cuda:0 f32[3, 4]"
# t4 = prims.mul(t0, t1) # t4: "cuda:0 f32[3, 4]"

# thunder.func_39:20: t5 = ltorch.mul(t2, t3) # t5: "cuda:0 f32[3, 4]"
t5 = ltorch.mul(t2, t3) # t5: "cuda:0 f32[3, 4]"
# t5 = prims.mul(t2, t3) # t5: "cuda:0 f32[3, 4]"

# thunder.func_39:21: t6 = ltorch.mul(t5, 1) # t6: "cuda:0 f32[3, 4]"
t6 = ltorch.mul(t5, 1) # t6: "cuda:0 f32[3, 4]"
# _ = prims.convert_element_type(1, float)
# t6 = prims.mul(t5, 1.0) # t6: "cuda:0 f32[3, 4]"

# thunder.func_39:22: t7 = prims.uniform((3, 4), 0.0, 1.0, device=devices.Device("cuda:0"), dtype=dtypes.float16) # t7: "cuda:0 f16[3, 4]"
t14 = prims.uniform((3, 4), 0.0, 1.0, device=devices.Device("cuda:0"), dtype=dtypes.float16) # t14: "cuda:0 f16[3, 4]"

# /home/iyashchuk/dev/pytorch/main/torch/autograd/grad_mode.py:186: torch._C._set_grad_enabled(mode)
return (t4, t5, t6, t14)
```
Why is `t14` not renamed to `t7` and all other variables are renamed?
The renaming is happening at https://github.com/Lightning-AI/lightning-thunder/blob/9f6e5b14e7a0fc6c96cca254540666d899df60b2/thunder/core/jit_ext.py#L1822-L1823

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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 at thunder/core/jit_ext.py around lines 1822-1823, where the proxy renaming occurs, and reproduce the initial trace using the example from test_core.py::test_cse. Compare the generated names for the uniform operation and the other proxies; done means the initial trace consistently renames that proxy as expected rather than leaving it as t14.

Written by the indexing model from the issue text.

Assessment

Tech stack
python, pytorch
Domain
compilers
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Clearly specified
Newbie friendliness
50/100

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