[bug/feature][relax.frontend.torch] from_exported_program rejects randn.default (blocks repro that stresses advanced-indexing write + tuple output)

[tinywisdom]

Actual behavior

Importing an exported PyTorch program fails early in TVM Relax Torch frontend with:

AssertionError: Unsupported function types ['randn.default']

The model is intentionally small and uses advanced indexing write (two index tensors on the same dims) and returns a tuple (y, L) to exercise relax::Tuple creation. However, the importer aborts first due to missing coverage for aten::randn.default, so we cannot reach the later code path.

Environment

• OS: (Ubuntu 22.04.4 LTS (x86_64))
• TVM version: (release v0.21.0)
• Python: (3.10.16)
• LLVM: (17.0.6)
• Pytorch: (2.8.0)

Steps to reproduce

# Purpose: Trigger importer on advanced indexing (two index tensors) + tuple outputs.
# Current blocker: Unsupported function types ['randn.default'].

import torch
import torch.nn as nn
import torch.nn.functional as F

def main():
    print("==== Versions ====")
    import tvm
    print("PyTorch:", torch.__version__)
    print("TVM    :", tvm.__version__)

    torch.manual_seed(0)
    N = 5

    class M(nn.Module):
        def forward(self, x):
            L = torch.zeros(N, N, dtype=x.dtype, device=x.device)
            idx = torch.arange(N, device=x.device)
            v = torch.randn(N, device=x.device)       # <-- aten::randn.default
            v = F.elu(v) + 1.0 + 1e-8                # keep values > 0
            L[idx, idx] = v                           # advanced indexing write
            y = x + 1
            return y, L                                # tuple output -> relax::Tuple

    m = M().eval()
    ex_in = torch.randn(2, N)

    # 1) export OK
    from torch.export import export as torch_export
    ep = torch_export(m, (ex_in,))
    print("torch.export: OK")

    # 2) TVM import -> fails on unsupported randn
    from tvm.relax.frontend.torch import from_exported_program
    print("about to call from_exported_program(ep)...")
    mod = from_exported_program(ep)  # <-- aborts with Unsupported function types ['randn.default']
    print("from_exported_program: OK (if you see this, the randn support may have landed)")

if __name__ == "__main__":
    main()

Output

==== Versions ====
PyTorch: 2.8.0a0+gitba56102
TVM    : 0.21.0
torch.export: OK
about to call from_exported_program(ep)...
Traceback (most recent call last):
  ...
  File ".../tvm/relax/frontend/torch/base_fx_graph_translator.py", line 116, in _check_unsupported_func_type
    assert not missing_func_types, f"Unsupported function types {missing_func_types}"
AssertionError: Unsupported function types ['randn.default']

Triage

• needs-triage
• bug