Fix deep recursion with siblings (#1462)

* fix recursion with siblings

* fix

* add test

* increase tol

mlx/array.cpp

@@ -242,25 +242,35 @@ array::ArrayDesc::~ArrayDesc() {
   // This calls recursively the destructor and can result in stack overflow, we
   // instead put them in a vector and destroy them one at a time resulting in a
   // max stack depth of 2.
+  if (inputs.empty()) {
+    return;
+  }
+
   std::vector<std::shared_ptr<ArrayDesc>> for_deletion;
 
-  for (array& a : inputs) {
-    if (a.array_desc_.use_count() == 1) {
+  auto append_deletable_inputs = [&for_deletion](ArrayDesc& ad) {
+    std::unordered_map<std::uintptr_t, array> input_map;
+    for (array& a : ad.inputs) {
+      if (a.array_desc_) {
+        input_map.insert({a.id(), a});
+      }
+    }
+    ad.inputs.clear();
+    for (auto& [_, a] : input_map) {
+      if (a.array_desc_.use_count() <= a.siblings().size() + 1) {
         for_deletion.push_back(std::move(a.array_desc_));
       }
     }
+  };
+
+  append_deletable_inputs(*this);
 
   while (!for_deletion.empty()) {
     // top is going to be deleted at the end of the block *after* the arrays
     // with inputs have been moved into the vector
     auto top = std::move(for_deletion.back());
     for_deletion.pop_back();
-
-    for (array& a : top->inputs) {
-      if (a.array_desc_.use_count() == 1) {
-        for_deletion.push_back(std::move(a.array_desc_));
-      }
-    }
+    append_deletable_inputs(*top);
   }
 }
 

python/tests/test_array.py

@@ -1868,6 +1868,33 @@ class TestArray(mlx_tests.MLXTestCase):
         with self.assertRaises(ValueError):
             int(a)
 
+    def test_deep_graphs(self):
+        # The following tests should simply run cleanly without a segfault or
+        # crash due to exceeding recursion depth limits.
+
+        # Deep graph destroyed without eval
+        x = mx.array([1.0, 2.0])
+        for _ in range(100_000):
+            x = mx.sin(x)
+        del x
+
+        # Duplicate input deep graph destroyed without eval
+        x = mx.array([1.0, 2.0])
+        for _ in range(100_000):
+            x = x + x
+
+        # Deep graph with siblings destroyed without eval
+        x = mx.array([1, 2])
+        for _ in range(100_000):
+            x = mx.concatenate(mx.split(x, 2))
+        del x
+
+        # Deep graph with eval
+        x = mx.array([1.0, 2.0])
+        for _ in range(100_000):
+            x = mx.sin(x)
+        mx.eval(x)
+
 
 if __name__ == "__main__":
     unittest.main()

python/tests/test_conv.py

@@ -902,7 +902,7 @@ class TestConv(mlx_tests.MLXTestCase):
             dw10 = (cotan[1::s, :-1:s] * x).sum()
             dw11 = (cotan[1::s, 1::s] * x).sum()
             expected = mx.array([[dw00, dw01], [dw10, dw11]])
-            self.assertTrue(mx.allclose(dw, expected))
+            self.assertTrue(mx.allclose(dw, expected, rtol=1e-5, atol=1e-5))
 
     def test_conv_groups_grad(self):
         def fn(x, w):