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Editorial Team
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Asked: 2026-05-23T04:21:20+00:00

I was reading about the fact that LLVM v3 uses a static analysis of

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I was reading about the fact that LLVM v3 uses a static analysis of the code to implement a sort of automatic garbage collection that is prepared and done during compilation.

If the compiler statically inserts retains and releases then no runtime component for garbage collection is needed anymore or what?

Is this true? Will it work as a replacement of normal garbage collection either on iOS and OS X development? It is not clear what will happen..

Should we rely this kind of “static garbage collection”?

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  1. Editorial Team

    This is an interesting question: can a static analyzer implement a complete garbage collection system?

    The answer, it appears, would be no. The only way to implement garbage collection is knowing that an allocated piece of memory (e.g. an object instance) is no longer useable. In a runtime GC, this knowledge is gained by (effectively) scanning the stack and heap. Doing this at compile time would require analyzing all possible code paths through the system to determine where in its execution a particular allocation would no longer be reachable. This is equivalent to the halting problem. However, LLVM claims to support at least a limited form of automatic reference counting (inserting retain/releases) for you. See http://developer.apple.com/technologies/ios5/. I suspect that what LLVM is doing is not a full GC, it’s using the static analyzer to find when all references to an object go out of scope, and inserting appropriate retain/releases for you. The reference counting happens at run time, just as before. I highly doubt that it will do automatic free-ing of malloc’d blocks for you.

    If it works as advertised on the public site above, I’d say use it.

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