fix LtNode simplification when lhs and rhs contain same variables (ti…

…nygrad#3451)

* fix LtNode simplification when lhs and rhs contain same variables

`(Variable("a", 1, 5) < Variable("a", 1, 5))` should eval to `NumNode(0)`

* fix with less perf impact

test/unit/test_symbolic.py

@@ -413,9 +413,11 @@ def test_node_lt_node(self):
     c = Variable("c", 1, 10)
     d = Variable("d", 5, 10)
     # if the value is always the same, it folds to num
-    assert (a < b) == 1
-    assert (b < a) == 0
-    assert (d < a) == 0
+    assert (a < b) == NumNode(1)
+    assert (b < a) == NumNode(0)
+    assert (d < a) == NumNode(0)
+    assert (a < a) == NumNode(0)
+    assert (a > a) == NumNode(0)
     # if it remains as a LtNode, bool is always true and (min, max) == (0, 1)
     assert isinstance((a < c), LtNode) and (a < c).min == 0 and (a < c).max == 1
     assert a < c

tinygrad/shape/symbolic.py

@@ -168,6 +168,7 @@ def get_bounds(self) -> Tuple[int, int]: raise NotImplementedError("must be impl
 
 class LtNode(OpNode):
   def get_bounds(self) -> Tuple[int, int]:
+    if self.a == self.b: return (0, 0)
     if isinstance(self.b, int): return (1, 1) if self.a.max < self.b else (0, 0) if self.a.min >= self.b else (0, 1)
     return (1, 1) if self.a.max < self.b.min else (0, 0) if self.a.min >= self.b.max else (0, 1)
   def substitute(self, var_vals: Mapping[Variable, Union[NumNode, Variable]]) -> Node: