[Bug][Relax][Torch] Segfault in from_exported_program when model returns (Tensor, None) tuple

[tinywisdom]

Expected behavior

When converting a torch.export.exported program to TVM Relax via from_exported_program, if the model returns a tuple that contains both a Tensor and a None (non-tensor) element, TVM hits an FFI segfault during conversion/build.

Eager torch export works fine; the crash only happens inside the TVM frontend / build pipeline.

Actual behavior

torch==2.7.1a0+gite2d141d
tvm==0.21.0
tvm.relax.frontend.torch available: False
[step] from_exported_program ...
!!!!!!! TVM FFI encountered a Segfault !!!!!!!
  File "<unknown>", in tvm::relax::Tuple::Tuple(tvm::ffi::Array<tvm::RelaxExpr, void>, tvm::Span)
Segmentation fault (core dumped)

Environment

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

Steps to reproduce

# tvm_relax_export_none_repro.py
import torch
import torch.nn as nn

def versions():
    import tvm
    from tvm import relax
    print(f"torch=={torch.__version__}")
    print(f"tvm=={tvm.__version__}")
    print("tvm.relax.frontend.torch available:", hasattr(relax.frontend, "torch"))

class Tiny(nn.Module):
    def forward(self, x):
        # Key: returns (Tensor, None) — tuple with non-tensor element
        return x + 1, None

def repro():
    import tvm
    from tvm import relax
    from tvm.relax.frontend.torch import from_exported_program

    torch.manual_seed(0)
    m = Tiny().eval()
    x = torch.randn(2, 3)

    # 1) torch.export
    ep = torch.export.export(m, (x,))

    # 2) Relax frontend
    print("[step] from_exported_program ...")
    mod = from_exported_program(ep)

    # 3) build (usually crashes here)
    print("[step] relax.build ...")
    target = tvm.target.Target("llvm")
    ex = relax.build(mod, target=target)

    # 4) run (rarely reached)
    print("[step] vm run ...")
    vm = relax.VirtualMachine(ex, tvm.cpu(0))
    y = vm["main"](tvm.nd.from_dlpack(torch.utils.dlpack.to_dlpack(x)))
    print("OK, got outputs:", y)

if __name__ == "__main__":
    versions()
    repro()

Triage

• needs-triage
• bug

cc @junrushao @shingjan

[tlopex]

Closed as fixed by #18359