[Release/2.7][MPS] Warn that torch.compile is a prototype (pytorch#150550)

And reference pytorch#150121

Author: malfet

torch/_inductor/codegen/mps.py

@@ -2,6 +2,7 @@
 # Just an early prototype that shows that one can compile elementwise ops into a Metal shader
 from __future__ import annotations
 
+import functools
 import itertools
 from typing import Any, Optional, TYPE_CHECKING
 
@@ -701,11 +702,23 @@ def check_bounds(
         self.cse.generate(self.compute, line, assignment=False)
 
 
+@functools.cache
+def _warn_prototype() -> None:
+    import warnings
+
+    warnings.warn(
+        "torch.compile for Metal is an early protoype and might not work as expected."
+        " For details see https://github.com/pytorch/pytorch/issues/150121",
+        stacklevel=2,
+    )
+
+
 class MetalScheduling(SIMDScheduling):
     kernel_type = MetalKernel  # type: ignore[assignment]
 
     def __init__(self, scheduler: Optional[Scheduler]) -> None:
         super().__init__(scheduler)
+        _warn_prototype()
         wrapper = V.graph.wrapper_code
         if wrapper is not None:
             wrapper.header.splice(