[FRONTEND] Fix cast when both src_ty and dst_ty are of block_type (#1301)

Commonly used in atomic_rmw ops

python/test/unit/language/test_core.py

@@ -683,6 +683,22 @@ def test_tensor_atomic_rmw(shape, axis, device="cuda"):
     np.testing.assert_allclose(z_ref, to_numpy(z_tri), rtol=1e-4)
 
 
+def test_tensor_atomic_rmw_block(device="cuda"):
+    shape = (8, 8)
+
+    @triton.jit
+    def kernel(X, SHAPE0: tl.constexpr, SHAPE1: tl.constexpr):
+        off0 = tl.arange(0, SHAPE0)
+        off1 = tl.arange(0, SHAPE1)
+        offs = off0[:, None] * SHAPE1 + off1[None, :]
+        val = offs.to(tl.float32)
+        x = X + offs
+        tl.atomic_min(x, val)
+    x = torch.ones((8, 8), device=device, dtype=torch.float32)
+    kernel[(2,)](x, shape[0], shape[1])
+    assert torch.min(x).item() == 0.0
+
+
 def test_atomic_cas():
     # 1. make sure that atomic_cas changes the original value (Lock)
     @triton.jit