MemorySanitizer currently does a lot of pointer arithmetic using
ptrtoint+add+inttoptr instead of using getelementptr. As far as I can
tell, there is no need to use this pattern -- msan is not trying to
synthesize pointers with different provenance here. The pointers in
question stay within one object (like the TLS parameter area).
I suspect that this is just a leftover from pre-opaque-pointer types
where this was a natural way to perform offset arithmetic. Nowadays we
should just emit a getelementptr i8, aka ptradd.
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