[DependencyInjection] Make better use of memory and CPU during auto-discovery

Author: nicolas-grekas

Loader/FileLoader.php

@@ -119,8 +119,26 @@ public function registerClasses(Definition $prototype, string $namespace, string
         $autoconfigureAttributes = new RegisterAutoconfigureAttributesPass();
         $autoconfigureAttributes = $autoconfigureAttributes->accept($prototype) ? $autoconfigureAttributes : null;
         $classes = $this->findClasses($namespace, $resource, (array) $exclude, $autoconfigureAttributes, $source);
-        // prepare for deep cloning
-        $serializedPrototype = serialize($prototype);
+
+        $getPrototype = static fn () => clone $prototype;
+        $serialized = serialize($prototype);
+
+        // avoid deep cloning if no definitions are nested
+        if (strpos($serialized, 'O:48:"Symfony\Component\DependencyInjection\Definition"', 55)
+            || strpos($serialized, 'O:53:"Symfony\Component\DependencyInjection\ChildDefinition"', 55)
+        ) {
+            // prepare for deep cloning
+            foreach (['Arguments', 'Properties', 'MethodCalls', 'Configurator', 'Factory', 'Bindings'] as $key) {
+                $serialized = serialize($prototype->{'get'.$key}());
+
+                if (strpos($serialized, 'O:48:"Symfony\Component\DependencyInjection\Definition"')
+                    || strpos($serialized, 'O:53:"Symfony\Component\DependencyInjection\ChildDefinition"')
+                ) {
+                    $getPrototype = static fn () => $getPrototype()->{'set'.$key}(unserialize($serialized));
+                }
+            }
+        }
+        unset($serialized);
 
         foreach ($classes as $class => $errorMessage) {
             if (null === $errorMessage && $autoconfigureAttributes) {
@@ -147,7 +165,7 @@ public function registerClasses(Definition $prototype, string $namespace, string
             if (interface_exists($class, false)) {
                 $this->interfaces[] = $class;
             } else {
-                $this->setDefinition($class, $definition = unserialize($serializedPrototype));
+                $this->setDefinition($class, $definition = $getPrototype());
                 if (null !== $errorMessage) {
                     $definition->addError($errorMessage);