Fix cpu segfault (#1488)

* fix cpu segfault

* nit in tests

mlx/backend/common/compiled_cpu.cpp

@@ -14,6 +14,30 @@
 
 namespace mlx::core {
 
+struct CompilerCache {
+  struct DLib {
+    DLib(const std::string& libname) {
+      lib = dlopen(libname.c_str(), RTLD_NOW);
+      if (!lib) {
+        std::ostringstream msg;
+        msg << "Could not load C++ shared library " << dlerror();
+        throw std::runtime_error(msg.str());
+      }
+    }
+
+    ~DLib() {
+      dlclose(lib);
+    }
+    void* lib;
+  };
+  // Statics to cache compiled libraries and functions
+  std::list<DLib> libs;
+  std::unordered_map<std::string, void*> kernels;
+  std::shared_mutex mtx;
+};
+
+static CompilerCache cache{};
+
 // GPU compile is always available if the GPU is available and since we are in
 // this file CPU compile is also available.
 namespace detail {
@@ -30,35 +54,15 @@ std::string get_temp_file(const std::string& name) {
 void* compile(
     const std::string& kernel_name,
     const std::function<std::string(void)>& source_builder) {
-  struct DLib {
-    DLib(const std::string& libname) {
-      lib = dlopen(libname.c_str(), RTLD_NOW);
-      if (!lib) {
-        std::ostringstream msg;
-        msg << "Could not load C++ shared library " << dlerror();
-        throw std::runtime_error(msg.str());
-      }
-    }
-
-    ~DLib() {
-      dlclose(lib);
-    }
-    void* lib;
-  };
-  // Statics to cache compiled libraries and functions
-  static std::list<DLib> libs;
-  static std::unordered_map<std::string, void*> kernels;
-  static std::shared_mutex compile_mtx;
-
   {
-    std::shared_lock lock(compile_mtx);
-    if (auto it = kernels.find(kernel_name); it != kernels.end()) {
+    std::shared_lock lock(cache.mtx);
+    if (auto it = cache.kernels.find(kernel_name); it != cache.kernels.end()) {
       return it->second;
     }
   }
 
-  std::unique_lock lock(compile_mtx);
-  if (auto it = kernels.find(kernel_name); it != kernels.end()) {
+  std::unique_lock lock(cache.mtx);
+  if (auto it = cache.kernels.find(kernel_name); it != cache.kernels.end()) {
     return it->second;
   }
   std::string source_code = source_builder();
@@ -112,10 +116,10 @@ void* compile(
   }
 
   // load library
-  libs.emplace_back(shared_lib_path);
+  cache.libs.emplace_back(shared_lib_path);
 
   // Load function
-  void* fun = dlsym(libs.back().lib, kernel_name.c_str());
+  void* fun = dlsym(cache.libs.back().lib, kernel_name.c_str());
   if (!fun) {
     std::ostringstream msg;
     msg << "[Compile::eval_cpu] Failed to load compiled function "
@@ -123,7 +127,7 @@ void* compile(
         << dlerror();
     throw std::runtime_error(msg.str());
   }
-  kernels.insert({kernel_name, fun});
+  cache.kernels.insert({kernel_name, fun});
   return fun;
 }
 

mlx/compile_impl.h

@@ -6,6 +6,20 @@
 
 namespace mlx::core::detail {
 
-bool compile_available_for_device(const Device& device);
+// This is not part of the general C++ API as calling with a bad id is a bad
+// idea.
+std::function<std::vector<array>(const std::vector<array>&)> compile(
+    const std::function<std::vector<array>(const std::vector<array>&)>& fun,
+    std::uintptr_t fun_id,
+    bool shapeless = false,
+    std::vector<uint64_t> constants = {});
 
-}
+// Erase cached compile functions
+void compile_erase(std::uintptr_t fun_id);
+
+// Clear the compiler cache causing a recompilation of all compiled functions
+// when called again.
+void compile_clear_cache();
+
+bool compile_available_for_device(const Device& device);
+} // namespace mlx::core::detail

mlx/transforms_impl.h

@@ -16,21 +16,6 @@ std::vector<array> vmap_replace(
     const std::vector<int>& in_axes,
     const std::vector<int>& out_axes);
 
-// This is not part of the general C++ API as calling with a bad id is a bad
-// idea.
-std::function<std::vector<array>(const std::vector<array>&)> compile(
-    const std::function<std::vector<array>(const std::vector<array>&)>& fun,
-    std::uintptr_t fun_id,
-    bool shapeless = false,
-    std::vector<uint64_t> constants = {});
-
-// Erase cached compile functions
-void compile_erase(std::uintptr_t fun_id);
-
-// Clear the compiler cache causing a recompilation of all compiled functions
-// when called again.
-void compile_clear_cache();
-
 // Create an InTracing object during tracing operations to signify to the rest
 // of the codebase that we are during tracing so evals should not throw away
 // the graph.

python/src/ops.cpp

@@ -1323,10 +1323,7 @@ void init_ops(nb::module_& m) {
           start (float or int, optional): Starting value which defaults to ``0``.
           stop (float or int): Stopping value.
           step (float or int, optional): Increment which defaults to ``1``.
-          dtype (Dtype, optional): Specifies the data type of the output.
-            If unspecified will default to ``float32`` if any of ``start``,
-            ``stop``, or ``step`` are ``float``. Otherwise will default to
-            ``int32``.
+          dtype (Dtype, optional): Specifies the data type of the output. If unspecified will default to ``float32`` if any of ``start``, ``stop``, or ``step`` are ``float``. Otherwise will default to ``int32``.
 
       Returns:
           array: The range of values.

python/src/transforms.cpp

@@ -13,6 +13,7 @@
 
 #include "mlx/array.h"
 #include "mlx/compile.h"
+#include "mlx/compile_impl.h"
 #include "mlx/graph_utils.h"
 #include "mlx/transforms.h"
 #include "mlx/transforms_impl.h"

python/tests/test_conv_transpose.py

@@ -171,7 +171,7 @@ class TestConvTranspose(mlx_tests.MLXTestCase):
 
                 # use torch to compute ct
                 out_pt.retain_grad()
-                (out_pt - torch.randn_like(out_pt)).abs().sum().backward()
+                out_pt.sum().backward()
 
                 pt_grad_in = in_pt.grad.permute(0, 2, 1).numpy()
                 pt_grad_wt = wt_pt.grad.permute(1, 2, 0).numpy()
@@ -365,7 +365,7 @@ class TestConvTranspose(mlx_tests.MLXTestCase):
 
                 # use torch to compute ct
                 out_pt.retain_grad()
-                (out_pt - torch.randn_like(out_pt)).abs().sum().backward()
+                out_pt.sum().backward()
 
                 pt_grad_in = in_pt.grad.permute(0, 2, 3, 1).numpy()
                 pt_grad_wt = wt_pt.grad.permute(1, 2, 3, 0).numpy()
@@ -549,7 +549,7 @@ class TestConvTranspose(mlx_tests.MLXTestCase):
 
                 # use torch to compute ct
                 out_pt.retain_grad()
-                (out_pt - torch.randn_like(out_pt)).abs().sum().backward()
+                out_pt.sum().backward()
 
                 pt_grad_in = in_pt.grad.permute(0, 2, 3, 4, 1).numpy()
                 pt_grad_wt = wt_pt.grad.permute(1, 2, 3, 4, 0).numpy()