Raise error when autotune_with_torch_compile_fusion is set without torch_compile_fusion

Previously, setting autotune_with_torch_compile_fusion=True without
torch_compile_fusion=True was silently ignored. Now it raises
FusionAutotuneRequiresTorchCompileFusion at Settings construction time.

Author: yf225

helion/exc.py

@@ -310,6 +310,14 @@ class IncompatibleInterpretModes(BaseError):
     message = "TRITON_INTERPRET=1 and HELION_INTERPRET=1 cannot be used together. Please use only one of these debug modes at a time."
 
 
+class FusionAutotuneRequiresTorchCompileFusion(BaseError):
+    location_suffix = ""
+    message = (
+        "autotune_with_torch_compile_fusion=True requires torch_compile_fusion=True. "
+        "Either enable torch_compile_fusion or disable autotune_with_torch_compile_fusion."
+    )
+
+
 class MissingEnableTile(BaseError):
     message = (
         "HELION_BACKEND=tileir requires the Triton TileIR driver to be active. "

helion/runtime/settings.py

@@ -677,6 +677,9 @@ def __init__(self, **settings: object) -> None:
         if self.backend == "tileir" and os.environ.get("ENABLE_TILE", "0") != "1":
             raise exc.MissingEnableTile
 
+        if self.autotune_with_torch_compile_fusion and not self.torch_compile_fusion:
+            raise exc.FusionAutotuneRequiresTorchCompileFusion
+
         self._check_ref_eager_mode_before_print_output_code()
 
     def to_dict(self) -> dict[str, object]: