Don't set replacement if lhs is in the free symbols of the rhs (pytorch#139250)

Fixes python test/dynamo/test_functions.py FunctionTests.test_is_integer

when we turn off specialize float on eager: pytorch#138915

Pull Request resolved: pytorch#139250
Approved by: https://github.com/ezyang

Author: bobrenjc93

test/dynamo/test_unspec.py

@@ -601,6 +601,19 @@ def fn(x):
         compl_fn = torch.compile(fn, dynamic=True, backend="eager")
         self.assertEqual(compl_fn(inputs), fn(inputs))
 
+    @torch._dynamo.config.patch(specialize_float=False)
+    def test_symfloat_no_replacement(self):
+        # See https://github.com/pytorch/pytorch/pull/139250 for more context
+        # The high level idea is if we don't want to set a replacement where a
+        # symbol is on both the right and left side, otherwise we'll end up
+        # in an infinite self._find recursion.
+        def fn(t, m):
+            return 2 * t if m.is_integer() else t
+
+        t = torch.tensor([1])
+        compl_fn = torch.compile(fn, dynamic=True, backend="eager")
+        self.assertEqual(fn(t, 1.0), compl_fn(t, 1.0))
+
     @torch._dynamo.config.patch(specialize_float=False)
     def test_unspec_roundtrip_float_input(self):
         def f(x, y):

torch/fx/experimental/symbolic_shapes.py

@@ -5591,10 +5591,12 @@ def _set_replacement(self, a: sympy.Symbol, tgt: sympy.Expr, msg: str) -> None:
         Adds or updates a replacement for a symbol.
         Use this instead of `self.replacements[a] = tgt`.
         """
-
         if tgt == self.replacements.get(a, None):
             return
 
+        if a in tgt.free_symbols:
+            return
+
         # Precondition: a == tgt
         assert isinstance(a, sympy.Symbol)