[Bug] MetaSchedule tuning exits successfully with zero candidates measured on Windows #20314

Could you check whether this is expected on Windows? I ran into this while building a small no-Python TVM integration for Pascal and C#.

Expected behavior

Candidates are measured, or tuning fails with the underlying runner error instead of exiting successfully.

Actual behavior

With the stock Windows wheel, MetaSchedule tuning finishes with exit code 0 even though the runner fails on every candidate. The summary shows Total trials: 0 (0/217 candidates measured), so no candidates are successfully measured.

The failure occurs while loading each built candidate. In the minimal reproducer, LocalRunner loads the built .tar artifact and relinks it with clang; on the tested setup, the default configuration first fails because clang is not found on PATH, and once clang is available the link still fails on the default target (x86_64) and without the TVM runtime import libraries. The link succeeds with TVM_WIN_TARGET=x86_64-pc-windows-msvc and a TVM_WIN_CC wrapper that invokes clang and adds the TVM runtime import libraries.

The 0/217 result was from ResNet-50. In a separate two-convolution smoke test of the same workaround, 16/16 candidates were measured. I reproduced the original failure with the same stock wheel on two Windows machines.

I'm not sure whether the intended behavior is for the Windows relink path to provide this configuration, or for tuning to fail when the linker fails.

Environment

apache-tvm 0.26.0 (py3-none-win_amd64 wheel), Python 3.12.10, Windows 11 x64.

Steps to reproduce

Minimal reproducer for the runner failure:

import tvm
from tvm import te
from tvm.s_tir.meta_schedule.builder import LocalBuilder, BuilderInput
from tvm.s_tir.meta_schedule.runner import LocalRunner, RunnerInput
from tvm.s_tir.meta_schedule.arg_info import TensorInfo

N = 256
A = te.placeholder((N, N), "float32", name="A")
B = te.placeholder((N, N), "float32", name="B")
C = te.compute((N, N), lambda i, j: A[i, j] + B[i, j], name="C")
mod = tvm.IRModule({"main": te.create_prim_func([A, B, C])})
target = tvm.target.Target({"kind": "llvm", "num-cores": 8})

(built,) = LocalBuilder().build([BuilderInput(mod, target)])
assert built.error_msg is None, built.error_msg

args = [TensorInfo("float32", (N, N)) for _ in range(3)]
(future,) = LocalRunner().run([RunnerInput(str(built.artifact_path), "cpu", args)])
result = future.result()
print("run_secs :", result.run_secs)   # None on Windows
print("error_msg:", result.error_msg)  # the linker error below

FileNotFoundError: [WinError 2]   # subprocess.Popen(["clang", ...])
RuntimeError: Can not find the LLVM clang for Windows clang.exe. Make sure it's installed and the installation directory is in the %PATH% environment variable.

Triage

• needs-triage