Shorter kernel name for Windows (#1701)

* Shorter kernel name for Windows

* Only hash the clipped part

mlx/backend/common/compiled_cpu.cpp

@@ -68,15 +68,20 @@ void* compile(
   std::string source_code = source_builder();
   std::string kernel_file_name;
 
-  // Deal with long kernel names. Maximum length for files on macOS is 255
-  // characters. Clip file name with a little extra room and append a 16
-  // character hash.
+  // Deal with long kernel names. Maximum length for filename on macOS is 255
+  // characters, and on Windows the maximum length for whole path is 260. Clip
+  // file name with a little extra room and append a 16 character hash.
+#ifdef _WIN32
+  constexpr int max_file_name_length = 140;
+#else
   constexpr int max_file_name_length = 245;
+#endif
   if (kernel_name.size() > max_file_name_length) {
     std::ostringstream file_name;
     file_name
         << std::string_view(kernel_name).substr(0, max_file_name_length - 16);
-    auto file_id = std::hash<std::string>{}(kernel_name);
+    auto file_id =
+        std::hash<std::string>{}(kernel_name.substr(max_file_name_length - 16));
     file_name << "_" << std::hex << std::setw(16) << file_id << std::dec;
     kernel_file_name = file_name.str();
   } else {