Do not export sampler for device==mps && dtype==bfloat16

optimum/exporters/executorch/integrations.py

@@ -919,15 +919,27 @@ def export(
             example_cache_position,
         )
 
-        self.exported_sampler = self._export_sampler(
-            torch.randn((1, 1, self.config.vocab_size), dtype=self.model.dtype, device=self.model.device)
-        )
+        # Skip sampler export for MPS + bfloat16 due to Metal shader compilation error
+        # (assigning float to bfloat in generated shader code)
+        is_mps_bfloat16 = str(self.model.device).startswith("mps") and self.model.dtype == torch.bfloat16
+        if is_mps_bfloat16:
+            logging.warning(
+                "Skipping sampler export for MPS + bfloat16 due to Metal shader compilation issues. "
+                "The runner will use CPU-based sampling instead."
+            )
+            self.exported_sampler = None
+        else:
+            self.exported_sampler = self._export_sampler(
+                torch.randn((1, 1, self.config.vocab_size), dtype=self.model.dtype, device=self.model.device)
+            )
 
-        return {
+        result = {
             "encoder": self.exported_encoder,  # Not called "text_encoder" because the encoder could be non-text too, e.g. Whisper.
             "text_decoder": self.exported_decoder,
-            "sampler": self.exported_sampler,
         }
+        if self.exported_sampler is not None:
+            result["sampler"] = self.exported_sampler
+        return result
 
     def generate(self, prompt_token_ids, max_new_tokens):
         with torch.no_grad():