Do not trigger Intervals::isSubsetOf() over and over again for platform packages

src/Composer/DependencyResolver/PoolBuilder.php

@@ -245,6 +245,11 @@ class PoolBuilder
 
     private function markPackageNameForLoading(Request $request, $name, ConstraintInterface $constraint)
     {
+        // Skip platform requires at this stage
+        if (PlatformRepository::isPlatformPackage($name)) {
+            return;
+        }
+
         // Root require (which was not unfixed) already loaded the maximum range so no
         // need to check anything here
         if (isset($this->maxExtendedReqs[$name])) {

src/Composer/Repository/PlatformRepository.php

@@ -593,4 +593,21 @@ class PlatformRepository extends ArrayRepository
 
         $this->addPackage($lib);
     }
+
+    /**
+     * Check if a package name is a platform package.
+     *
+     * @param $name
+     * @return bool
+     */
+    public static function isPlatformPackage($name)
+    {
+        static $cache = array();
+
+        if (isset($cache[$name])) {
+            return $cache[$name];
+        }
+
+        return $cache[$name] = (bool) preg_match(PlatformRepository::PLATFORM_PACKAGE_REGEX, $name);
+    }
 }