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Garbage collection and MM

Garbage collection and MM

Posted Mar 8, 2007 12:22 UTC (Thu) by nix (subscriber, #2304)
In reply to: Garbage collection and MM by aanno
Parent article: Short topics in memory management

Yes, GCC 3.0 did start using GC (because the lifetime rules of objects in the compiler were unfathomably complex). It fixed an unknown but large number of bugs... and slowed down the compiler a *lot* due to cache locality issues.

Years ago now, someone (Mike Stump?) ran some benchmarks that showed GCC incurring cache stalls every *twenty instructions* or thereabouts. Small wonder that it slowed down!

Careful moves are now underway (and have been for a while) to migrate objects with simple lifetime rules back into obstacks. The obstacks are still garbage-collected, but the obstack is a *single* GCed object with good cache locality, where the myriads of objects it replaces were not.

I doubt GCC will ever leave GCC, either: for objects with complex lifetime rules, there's really no maintainable alternative. But for the simple ones, using suballocators with better cache locality (like obstacks) is a good idea.


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