throw for certain cases of non captured inputs in compile (#1401)

mlx/compile.cpp

@@ -306,21 +306,27 @@ std::pair<std::vector<array>, std::vector<array>> compile_trace(
 // Traverses the graph to build a tape and a map of array ids to their parents
 std::pair<std::vector<array>, ParentsMap> compile_dfs(
     const std::vector<array>& inputs,
-    const std::vector<array>& outputs) {
+    const std::vector<array>& outputs,
+    const std::vector<array>& original_inputs) {
   std::function<void(const array&)> recurse;
   std::vector<array> tape;
   std::unordered_set<std::uintptr_t> input_set;
+  std::unordered_set<std::uintptr_t> original_input_set;
   std::unordered_map<std::uintptr_t, std::vector<std::pair<array, int>>>
       parents_map;
   for (int i = 0; i < inputs.size(); ++i) {
-    auto in = inputs[i];
-    input_set.insert(in.id());
+    input_set.insert(inputs[i].id());
+    original_input_set.insert(original_inputs[i].id());
   }
 
   // DFS the graph to build the tape, and log parents and scalars
   std::unordered_set<std::uintptr_t> cache;
   recurse = [&](const array& a) {
     auto id = a.id();
+    if (original_input_set.find(id) != original_input_set.end()) {
+      throw std::invalid_argument(
+          "[compile] Attempting to compile a function with uncaptured inputs is not allowed.");
+    }
     if (cache.find(id) != cache.end()) {
       return;
     }
@@ -833,7 +839,7 @@ std::function<std::vector<array>(const std::vector<array>&)> compile(
       std::unordered_map<uintptr_t, std::vector<std::pair<array, int>>>
           parents_map;
       std::tie(entry.tape, parents_map) =
-          compile_dfs(entry.inputs, entry.outputs);
+          compile_dfs(entry.inputs, entry.outputs, inputs);
 
       // Simplify the tape
       if (compile_mode() != CompileMode::no_simplify) {

mlx/fast.cpp

@@ -972,7 +972,7 @@ void write_signature(
       {"threadgroups_per_grid", "uint3"},
       {"threads_per_grid", "uint3"},
       {"threads_per_simdgroup", "uint"},
-      {"thread_per_threadgroup", "uint3"},
+      {"threads_per_threadgroup", "uint3"},
   };
   std::vector<std::pair<std::string, std::string>> attrs;
   for (const auto& [attr, dtype] : metal_attributes) {

python/tests/test_compile.py

@@ -733,6 +733,31 @@ class TestCompile(mlx_tests.MLXTestCase):
             expected = fn(x)
             self.assertTrue(mx.array_equal(expected, out))
 
+    def test_compile_without_captured_inputs(self):
+        x = mx.array([1, 2, 3]) + 2
+
+        def fn(a):
+            y = x + 1
+            return a + y
+
+        with self.assertRaises(ValueError):
+            y = mx.compile(fn)(x)
+
+        x = mx.array([1.0, 2.0]) + mx.array([1.0, 2.0])
+        y = None
+
+        def fn(x):
+            nonlocal y
+            if y is None:
+                y = mx.array([1.0, 2.0])
+
+            y = y + x
+            return y
+
+        fn(x)
+        with self.assertRaises(ValueError):
+            y = mx.compile(fn)(x)
+
 
 if __name__ == "__main__":
     unittest.main()

python/tests/test_fast.py

@@ -689,6 +689,27 @@ class TestFast(mlx_tests.MLXTestCase):
         )
         self.assertTrue(mx.allclose(out[0], mx.exp(a)))
 
+    @unittest.skipIf(not mx.metal.is_available(), "Metal is not available")
+    def test_custom_kernel_attributes(self):
+        a = mx.zeros(shape=(1, 1))
+        kernel = mx.fast.metal_kernel(
+            name="test_fun",
+            input_names=["a"],
+            output_names=["out"],
+            source="""
+                out[0] = threads_per_threadgroup.x;
+            """,
+        )
+        out = kernel(
+            inputs=[a],
+            grid=(2, 1, 1),
+            threadgroup=(2, 1, 1),
+            output_shapes=[(1, 1)],
+            output_dtypes=[mx.uint32],
+            stream=mx.gpu,
+        )[0]
+        self.assertEqual(out.item(), 2)
+
 
 if __name__ == "__main__":
     unittest.main()