Analyzing CFG to find common resource exploitation patterns,
like to determine sites of first and last usage of resources in order to check(provide) safe initialization or releasing.

**Usecases:**
* resource using in loop: acquire resource right before loop, and freeing right after that.
* group of probable first/last using: every site in the group should treat resource as lazy(with safety check), 
 and eager otherwise

**Examples:**
* appending to a file
* memory management