diff --git a/src/CodeCoverage.php b/src/CodeCoverage.php
index d1ac2e9e7..55520571e 100644
--- a/src/CodeCoverage.php
+++ b/src/CodeCoverage.php
@@ -81,6 +81,20 @@ class PHP_CodeCoverage
      */
     private $tests = [];
 
+    /**
+     * Determine if the data has been initialized or not
+     *
+     * @var bool
+     */
+    private $isInitialized = false;
+
+    /**
+     * Determine whether we need to check for dead and unused code on each test
+     *
+     * @var bool
+     */
+    private $shouldCheckForDeadAndUnused = true;
+
     /**
      * Constructor.
      *
@@ -121,6 +135,7 @@ public function getReport()
      */
     public function clear()
     {
+        $this->isInitialized = false;
         $this->currentId = null;
         $this->data      = [];
         $this->tests     = [];
@@ -206,9 +221,13 @@ public function start($id, $clear = false)
             $this->clear();
         }
 
+        if ($this->isInitialized === false) {
+            $this->initializeData();
+        }
+
         $this->currentId = $id;
 
-        $this->driver->start();
+        $this->driver->start($this->shouldCheckForDeadAndUnused);
     }
 
     /**
@@ -580,13 +599,7 @@ private function addUncoveredFilesFromWhitelist()
                 continue;
             }
 
-            if ($this->processUncoveredFilesFromWhitelist) {
-                $this->processUncoveredFileFromWhitelist(
-                    $uncoveredFile,
-                    $data,
-                    $uncoveredFiles
-                );
-            } else {
+            if (!$this->processUncoveredFilesFromWhitelist) {
                 $data[$uncoveredFile] = [];
 
                 $lines = count(file($uncoveredFile));
@@ -600,31 +613,6 @@ private function addUncoveredFilesFromWhitelist()
         $this->append($data, 'UNCOVERED_FILES_FROM_WHITELIST');
     }
 
-    /**
-     * @param string $uncoveredFile
-     * @param array  $data
-     * @param array  $uncoveredFiles
-     */
-    private function processUncoveredFileFromWhitelist($uncoveredFile, array &$data, array $uncoveredFiles)
-    {
-        $this->driver->start();
-        include_once $uncoveredFile;
-        $coverage = $this->driver->stop();
-
-        foreach ($coverage as $file => $fileCoverage) {
-            if (!isset($data[$file]) &&
-                in_array($file, $uncoveredFiles)) {
-                foreach (array_keys($fileCoverage) as $key) {
-                    if ($fileCoverage[$key] == PHP_CodeCoverage_Driver::LINE_EXECUTED) {
-                        $fileCoverage[$key] = PHP_CodeCoverage_Driver::LINE_NOT_EXECUTED;
-                    }
-                }
-
-                $data[$file] = $fileCoverage;
-            }
-        }
-    }
-
     /**
      * Returns the lines of a source file that should be ignored.
      *
@@ -897,4 +885,45 @@ private function selectDriver()
             return new PHP_CodeCoverage_Driver_Xdebug;
         }
     }
+
+    /**
+     * If we are processing uncovered files from whitelist,
+     * we can initialize the data before we start to speed up the tests
+     */
+    protected function initializeData()
+    {
+        $this->isInitialized = true;
+
+        if ($this->processUncoveredFilesFromWhitelist) {
+
+            $this->shouldCheckForDeadAndUnused = false;
+
+            $this->driver->start(true);
+
+            foreach ($this->filter->getWhitelist() as $file) {
+                if ($this->filter->isFile($file)) {
+                    include_once($file);
+                }
+            }
+
+            $data = [];
+            $coverage = $this->driver->stop();
+
+            foreach ($coverage as $file => $fileCoverage) {
+                if ($this->filter->isFiltered($file)) {
+                    continue;
+                }
+
+                foreach (array_keys($fileCoverage) as $key) {
+                    if ($fileCoverage[$key] == PHP_CodeCoverage_Driver::LINE_EXECUTED) {
+                        $fileCoverage[$key] = PHP_CodeCoverage_Driver::LINE_NOT_EXECUTED;
+                    }
+                }
+
+                $data[$file] = $fileCoverage;
+            }
+
+            $this->append($data, 'UNCOVERED_FILES_FROM_WHITELIST');
+        }
+    }
 }
diff --git a/src/CodeCoverage/Driver.php b/src/CodeCoverage/Driver.php
index 8635acefe..4452ec02e 100644
--- a/src/CodeCoverage/Driver.php
+++ b/src/CodeCoverage/Driver.php
@@ -36,7 +36,7 @@ interface PHP_CodeCoverage_Driver
     /**
      * Start collection of code coverage information.
      */
-    public function start();
+    public function start($determineUnusedAndDead = true);
 
     /**
      * Stop collection of code coverage information.
diff --git a/src/CodeCoverage/Driver/HHVM.php b/src/CodeCoverage/Driver/HHVM.php
index a9d8f0cef..4250091a3 100644
--- a/src/CodeCoverage/Driver/HHVM.php
+++ b/src/CodeCoverage/Driver/HHVM.php
@@ -19,7 +19,7 @@ class PHP_CodeCoverage_Driver_HHVM extends PHP_CodeCoverage_Driver_Xdebug
     /**
      * Start collection of code coverage information.
      */
-    public function start()
+    public function start($determineUnusedAndDead = true)
     {
         xdebug_start_code_coverage();
     }
diff --git a/src/CodeCoverage/Driver/PHPDBG.php b/src/CodeCoverage/Driver/PHPDBG.php
index 2c39c8c80..92f78106f 100644
--- a/src/CodeCoverage/Driver/PHPDBG.php
+++ b/src/CodeCoverage/Driver/PHPDBG.php
@@ -37,7 +37,7 @@ public function __construct()
     /**
      * Start collection of code coverage information.
      */
-    public function start()
+    public function start($determineUnusedAndDead = true)
     {
         phpdbg_start_oplog();
     }
diff --git a/src/CodeCoverage/Driver/Xdebug.php b/src/CodeCoverage/Driver/Xdebug.php
index ed9a7035b..f8e9a9f03 100644
--- a/src/CodeCoverage/Driver/Xdebug.php
+++ b/src/CodeCoverage/Driver/Xdebug.php
@@ -16,6 +16,13 @@
  */
 class PHP_CodeCoverage_Driver_Xdebug implements PHP_CodeCoverage_Driver
 {
+    /**
+     * Cache the number of lines for each file
+     *
+     * @var array
+     */
+    private $cacheNumLines = [];
+
     /**
      * Constructor.
      */
@@ -36,9 +43,13 @@ public function __construct()
     /**
      * Start collection of code coverage information.
      */
-    public function start()
+    public function start($determineUnusedAndDead = true)
     {
-        xdebug_start_code_coverage(XDEBUG_CC_UNUSED | XDEBUG_CC_DEAD_CODE);
+        if ($determineUnusedAndDead) {
+            xdebug_start_code_coverage(XDEBUG_CC_UNUSED | XDEBUG_CC_DEAD_CODE);
+        } else {
+            xdebug_start_code_coverage();
+        }
     }
 
     /**
@@ -85,13 +96,17 @@ private function cleanup(array $data)
      */
     private function getNumberOfLinesInFile($file)
     {
-        $buffer = file_get_contents($file);
-        $lines  = substr_count($buffer, "\n");
+        if (!isset($this->cacheNumLines[$file])) {
+            $buffer = file_get_contents($file);
+            $lines  = substr_count($buffer, "\n");
+
+            if (substr($buffer, -1) !== "\n") {
+                $lines++;
+            }
 
-        if (substr($buffer, -1) !== "\n") {
-            $lines++;
+            $this->cacheNumLines[$file] = $lines;
         }
 
-        return $lines;
+        return $this->cacheNumLines[$file];
     }
 }