https://msdn.microsoft.com/en-us/library/windows/desktop/bb509602(v=vs.85).aspx
Unroll the loop until it stops executing. Can optionally specify the maximum number of times the loop is to execute. Not compatible with the [loop] attribute
[unroll(num)] for(int i;i<num;i++)
原文：http://www.cnblogs.com/minggoddess/p/4482944.html