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Comment on Emacs internals: Tagged pointers vs. C++ std:variant and LLVM (Part 3)parent

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Pointer provenance is not properly defined in C or C++. (There is a C TS that introduces pointer provenance, but it's not part of the main standard).

The problem of pointer provenance is more finding a workable theoretical model rather than one causing miscompiles on realistic code. While there are definitely miscompiles on carefully constructed examples, I'm not aware of any bugs on actual code. This is in comparison to topics like restrict(/noalias) semantics or lifetime semantics, where there is a steady drip of bug reports that turn out to be actual optimization failures.

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