Eliminate these two global vars (well, fields in the global PL_reg_state), that hold the regex super-liner cache. PL_reg_poscache_size gets replaced with a field in the local regmatch_info struct, while PL_reg_poscache (which needs freeing at end of pattern execution or on croak()), goes in the regmatch_info_aux struct. Note that this includes a slight change in behaviour. Each regex execution now has its own private poscache pointer, initially null. If the super-linear behaviour is detected, the cache is malloced, used for the duration of the pattern match, then freed. The former behaviour allocated a global poscache on first use, which was retained between regex executions. Since the poscache could between 0.25 and 2x the size of the string being matched, that could potentially be a big buffer lying around unused. So we save memory at the expense of a new malloc/free for every regex that triggers super-linear behaviour. The old behaviour saved the old pointer on reentrancy, then restored the old one (and possibly freed the new buffer) at exit. Except it didn't for (?{}), so /(?{ m{something-that-triggers-super-linear-cache} })/ would leak each time the inner regex was called. This is now fixed automatically.