As previously reported by @flaushi in #7471 (comment), we discovered

that binding a parameter causes a `ClassMetadataFactory#getClassMetadata()` call, which in turn leads to large performance
regression when using any `object` type as parameter.

Following two snippets lead to an internal `ClassMetadataFactory#getClassMetadata()` call, which in turn leads to an
exception being thrown and garbage collected, plus multiple associated performance implications:

```php
$query->setParameter('foo', new DateTime());
$query->getResult();
```

```php
$query->setParameter('foo', new DateTime(), DateTimeType::NAME);
$query->getResult();
```

This is due to following portion of code:

https://github.com/doctrine/doctrine2/blob/434820973cadf2da2d66e7184be370084cc32ca8/lib/Doctrine/ORM/Query.php#L406-L409

Notice how `$value = $this->processParameterValue($value);` happens before attempting to infer the type for the parameter value.

That call leads to this segment being reached, which leads to the regression:

https://github.com/doctrine/doctrine2/blob/434820973cadf2da2d66e7184be370084cc32ca8/lib/Doctrine/ORM/AbstractQuery.php#L423-L433

Assuming the bound parameter type is provided, we can completely skip attempting to introspect the given object:

```php
$query->setParameter('foo', new DateTime(), DateTimeType::NAME);
$query->getResult();
```

Processing the parameter value is not needed in this case, so we can safely skip that logic for all known parameters.
In order to not introduce a BC break or change the `AbstractQuery#processParameterValue()` implementation, we could filter
out all parameters for which the type is given upfront, and later on merge them back in instead.

The test expectation to be set is for `UnitOfWork#getSingleIdentifierValue()` to never be called.

tests/Doctrine/Tests/ORM/Query/QueryTest.php

@@ -4,22 +4,25 @@
 
 namespace Doctrine\Tests\ORM\Query;
 
+use DateTime;
 use Doctrine\Common\Cache\ArrayCache;
 use Doctrine\Common\Collections\ArrayCollection;
 use Doctrine\DBAL\ParameterType;
-use Doctrine\ORM\EntityManagerInterface;
 use Doctrine\ORM\Internal\Hydration\IterableResult;
 use Doctrine\ORM\Query\Parameter;
 use Doctrine\ORM\Query\QueryException;
+use Doctrine\ORM\UnitOfWork;
 use Doctrine\Tests\Mocks\DriverConnectionMock;
+use Doctrine\Tests\Mocks\EntityManagerMock;
 use Doctrine\Tests\Mocks\StatementArrayMock;
 use Doctrine\Tests\Models\CMS\CmsAddress;
 use Doctrine\Tests\Models\CMS\CmsUser;
+use Doctrine\Tests\Models\Generic\DateTimeModel;
 use Doctrine\Tests\OrmTestCase;
 
 class QueryTest extends OrmTestCase
 {
-    /** @var EntityManagerInterface */
+    /** @var EntityManagerMock */
     protected $em;
 
     protected function setUp() : void
@@ -403,4 +406,22 @@ public function testResultCacheProfileCanBeRemovedViaSetter() : void
 
         self::assertAttributeSame(null, 'queryCacheProfile', $query);
     }
+
+    /** @group 7527 */
+    public function testValuesAreNotBeingResolvedForSpecifiedParameterTypes() : void
+    {
+        $unitOfWork = $this->createMock(UnitOfWork::class);
+
+        $this->_em->setUnitOfWork($unitOfWork);
+
+        $unitOfWork
+            ->expects(self::never())
+            ->method('getSingleIdentifierValue');
+
+        $query = $this->_em->createQuery('SELECT d FROM ' . DateTimeModel::class . ' d WHERE d.datetime = :value');
+
+        $query->setParameter('value', new DateTime(), Type::DATETIME);
+
+        self::assertEmpty($query->getResult());
+    }
 }

tests/Doctrine/Tests/OrmTestCase.php

@@ -18,6 +18,7 @@
 use Doctrine\ORM\EntityManagerInterface;
 use Doctrine\ORM\Mapping\Driver\AnnotationDriver;
 use Doctrine\ORM\Proxy\Factory\ProxyFactory;
+use Doctrine\Tests\Mocks;
 use function is_array;
 use function realpath;
 
@@ -78,17 +79,18 @@ protected function createAnnotationDriver($paths = [])
      * for a particular test,
      *
      * @param Connection|array  $conn
+     * @param mixed             $conf
      * @param EventManager|null $eventManager
      * @param bool              $withSharedMetadata
      *
-     * @return EntityManagerInterface
+     * @return Mocks\EntityManagerMock
      */
     protected function getTestEntityManager(
         $conn = null,
         $conf = null,
         $eventManager = null,
         $withSharedMetadata = true
-    ) {
+    ) : Mocks\EntityManagerMock {
         $metadataCache = $withSharedMetadata
             ? self::getSharedMetadataCacheImpl()
             : new ArrayCache();
@@ -129,7 +131,7 @@ protected function getTestEntityManager(
             $conn = DriverManager::getConnection($conn, $config, $eventManager);
         }
 
-        return Mocks\EntityManagerMock::create($conn, $config, $eventManager)->getWrappedEntityManager();
+        return Mocks\EntityManagerMock::create($conn, $config, $eventManager);
     }
 
     protected function enableSecondLevelCache($log = true)