[RFC] Intra-procedural Lifetime Analysis in Clang

Clang Frontend
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I’m really excited about this proposal! I think it could help WebKit a lot.

A few things I mentioned in today’s meet-up:

  • I believe this analysis can also enforce the noescape function argument attribute with relatively little additional effort. The strawman proposal is to model a noescape function argument as having an OriginSet that contains a single Loan that originates at the start of the function and invalidates at every function return point.
  • If we enforce noescape, then we can also turn this intra-procedural analysis into an inter-procedural analysis, still based on local reasoning, again with relatively little additional effort. The strawman proposal is: Any value whose OriginSet includes a non-opaque Loan, if passed as a function argument in a parameter slot that has no declared lifetime label (i.e., the declared function parameter has the Opaque origin), is by definition a Potential Dangling Pointer. (Since the dangling pointer is only potential, it probably only emits a warning in strict mode.) The programmer can cure this warning by marking the parameter noescape, [[clang::lifetimebound]], or [[clang::lifetime_capture_by]]. (Of course, the compiler may still signal a different warning if it finds a contradiction with these attributes.)
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