fix const bitcast should not be constant folded (#3743)

* fix const bitcast should not be constant folded

* fixed const bf16 creation

* LLVM still broken

test/test_dtype.py

@@ -137,16 +137,14 @@ class TestBFloat16(unittest.TestCase):
     assert tnp.dtype == np.float32
     np.testing.assert_allclose(tnp, np.array(data))
 
-  @unittest.expectedFailure
+  @unittest.skipIf(Device.DEFAULT=="LLVM", "broken for LLVM")
   def test_bf16_ones(self):
-    # TODO: fix this with correct bfloat16 cast
     t = Tensor.ones(3, 5, dtype=dtypes.bfloat16)
     assert t.dtype == dtypes.bfloat16
     np.testing.assert_allclose(t.numpy(), np.ones((3, 5)))
 
-  @unittest.expectedFailure
+  @unittest.skipIf(Device.DEFAULT=="LLVM", "broken for LLVM")
   def test_bf16_eye(self):
-    # TODO: fix this with correct bfloat16 cast
     t = Tensor.eye(3, dtype=dtypes.bfloat16)
     assert t.dtype == dtypes.bfloat16
     np.testing.assert_allclose(t.numpy(), np.eye(3))
@@ -256,6 +254,10 @@ class TestBitCast(unittest.TestCase):
     b = a.bitcast(dtypes.int32)
     assert b.numpy()[0] == 0x3f800000
 
+  def test_bitcast_const(self):
+    a = Tensor(1, dtype=dtypes.float32).bitcast(dtypes.uint32)
+    np.testing.assert_equal(a.numpy(), np.array(1, dtype=np.float32).view(np.uint32))
+
   def test_bitcast_upcasted(self):
     a = Tensor.zeros(100, 4, dtype=dtypes.int32).contiguous() + 0x3f800000
     b = a.bitcast(dtypes.float32)

tinygrad/codegen/uops.py

@@ -95,7 +95,7 @@ class PatternMatcher:
 constant_folder = PatternMatcher([
   # const rules
   ({"__name__": "root", "uop": UOps.GEP, "vin": ({"__name__": "c", "uop": UOps.CONST},)}, lambda root, c: UOp.const(root.dtype, c.arg)),
-  ({"__name__": "root", "uop": UOps.CAST, "vin": {"__name__": "c", "uop": UOps.CONST}}, lambda root, c: UOp.const(root.dtype, c.arg)),
+  ({"__name__": "root", "uop": UOps.CAST, "vin": {"__name__": "c", "uop": UOps.CONST, "arg": False}}, lambda root, c: UOp.const(root.dtype, c.arg)),
   # a phi without loops (len(vin)==2) is a noop
   ({"uop": UOps.PHI, "vin": ({}, {"__name__": "x"})}, lambda x: x),
   # x+-y -> x-y