Correct torch.xpu.is_bf16_supported return False if no XPU detected (#152317)

# Motivation
Fix https://github.com/pytorch/pytorch/issues/152301
When XPU is not available, calling `torch.xpu.is_bf16_supported()` still returns `True`, which is inconsistent with the expected behavior (should be False).

# Solution
Align to other backend, adding `including_emulation` to `torch.xpu.is_bf16_supported` and,
- return `False` if XPU is not available
- return `True` if `including_emulation` is True
- return `torch.xpu.get_device_properties().has_bfloat16_conversions` if `including_emulation` is False, it means if the device could generate SPIRV code for bf16.

Pull Request resolved: https://github.com/pytorch/pytorch/pull/152317
Approved by: https://github.com/EikanWang

test/test_xpu.py

@@ -22,7 +22,6 @@ from torch.testing._internal.common_utils import (
     find_library_location,
     IS_LINUX,
     IS_WINDOWS,
-    NoTest,
     run_tests,
     suppress_warnings,
     TEST_XPU,
@@ -31,10 +30,6 @@ from torch.testing._internal.common_utils import (
 from torch.utils.checkpoint import checkpoint_sequential
 
 
-if not TEST_XPU:
-    print("XPU not available, skipping tests", file=sys.stderr)
-    TestCase = NoTest  # noqa: F811
-
 TEST_MULTIXPU = torch.xpu.device_count() > 1
 
 cpu_device = torch.device("cpu")
@@ -74,6 +69,7 @@ _xpu_computation_ops = [
 ]
 
 
+@unittest.skipIf(not TEST_XPU, "XPU not available, skipping tests")
 class TestXpu(TestCase):
     def test_device_behavior(self):
         current_device = torch.xpu.current_device()
@@ -581,6 +577,7 @@ if __name__ == "__main__":
 instantiate_device_type_tests(TestXpu, globals(), only_for="xpu", allow_xpu=True)
 
 
+@unittest.skipIf(not TEST_XPU, "XPU not available, skipping tests")
 class TestXpuAutocast(TestAutocast):
     # These operators are not implemented on XPU backend and we can NOT fall back
     # them to CPU. So we have to skip them at this moment.
@@ -661,6 +658,7 @@ class TestXpuAutocast(TestAutocast):
             self.assertEqual(result.dtype, torch.float16)
 
 
+@unittest.skipIf(not TEST_XPU, "XPU not available, skipping tests")
 class TestXpuTrace(TestCase):
     def setUp(self):
         torch._C._activate_gpu_trace()
@@ -723,5 +721,17 @@ class TestXpuTrace(TestCase):
         self.mock.assert_called_once_with(event._as_parameter_.value)
 
 
+class TestXPUAPISanity(TestCase):
+    def test_is_bf16_supported(self):
+        self.assertEqual(
+            torch.xpu.is_bf16_supported(including_emulation=True),
+            torch.xpu.is_available(),
+        )
+
+    def test_get_arch_list(self):
+        if not torch.xpu._is_compiled():
+            self.assertEqual(len(torch.xpu.get_arch_list()), 0)
+
+
 if __name__ == "__main__":
     run_tests()

torch/xpu/__init__.py

@@ -66,9 +66,14 @@ def is_available() -> bool:
     return device_count() > 0
 
 
-def is_bf16_supported():
+def is_bf16_supported(including_emulation: bool = True) -> bool:
     r"""Return a bool indicating if the current XPU device supports dtype bfloat16."""
-    return True
+    if not is_available():
+        return False
+    return (
+        including_emulation
+        or torch.xpu.get_device_properties().has_bfloat16_conversions
+    )
 
 
 def is_initialized():