jit footguns test case on assign with same buffer outputs (#14209)

related https://github.com/tinygrad/tinygrad/issues/13364

test/test_jit_footguns.py

@@ -9,6 +9,7 @@ SILENT MISMATCHES (highest priority - wrong results, no error):
   class_method_shared_across_instances EASY could check if first arg is self and warn
   slice_assign_requires_realize      MED    assign graph not connected to read during JIT replay
   output_buffer_reuse                MED    performance tradeoff, could add option or better docs
+  multiple_outputs_same_intermediate MED    outputs derived from same intermediate get aliased during replay
   python_constants_frozen            HARD   inherent to tracing JITs
   conditional_branches_frozen        HARD   inherent to tracing JITs
 
@@ -50,6 +51,31 @@ class TestJitFootguns(unittest.TestCase):
 
     self.assertEqual([r1.item(), r2.item(), r3.item()], [2, 4, 6])
 
+  def test_multiple_outputs_same_intermediate(self):
+    """Multiple outputs derived from the same intermediate get aliased during replay."""
+    # TODO: fix this, clone should not be required, related to https://github.com/tinygrad/tinygrad/issues/13364
+    @TinyJit
+    def f_broken(buf, frame):
+      new_buf = buf[1:].cat(frame, dim=0)
+      return new_buf.contiguous(), new_buf[:1].contiguous()
+
+    @TinyJit
+    def f_fixed(buf, frame):
+      new_buf = buf[1:].cat(frame, dim=0)
+      return new_buf.clone().contiguous(), new_buf[:1].contiguous()
+
+    for f, should_work in [(f_broken, False), (f_fixed, True)]:
+      buf = Tensor([[0], [1], [2]]).contiguous().realize()
+      for i in range(4):
+        frame = Tensor([[10+i]]).contiguous().realize()
+        expected_first = buf[1:2].numpy().item()
+        new_buf, first = f(buf, frame)
+        if should_work:
+          self.assertEqual(first.numpy().item(), expected_first)
+        else:
+          if i >= 2: self.assertNotEqual(first.numpy().item(), expected_first)  # fails on 3rd iteration!
+        buf = new_buf
+
   def test_slice_assign_requires_realize(self):
     """Slice assign then read from same buffer - assign isn't connected to read without explicit realize()."""
     from tinygrad import Variable