function array_mergev($arrayv)

libphutil Technical Documentation (Core Utilities)

Merge a vector of arrays performantly. This has the same semantics as array_merge(), so these calls are equivalent:

array_merge($a, $b, $c);
array_mergev(array($a, $b, $c));

However, when you have a vector of arrays, it is vastly more performant to merge them with this function than by calling array_merge() in a loop, because using a loop generates an intermediary array on each iteration.