[PATCH] D90708: [LangRef] Clarify GEP inbounds wrapping semantics

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


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Comment at: llvm/docs/LangRef.rst:9782
+   means that it points into an allocated object, or to its end (which is one
+   byte past the last byte contained in the object). The only *in bounds*
+   address for a null pointer in the default address-space is the null pointer
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nlopes wrote:
> I still don't like the current writing. I would need to see some evidence from language standards that they require pointers past the end of objects.
What would be a better wording? "One past the end" is a term of art, and as such should be well understood: https://www.google.com/search?q=one+past+the+end


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Comment at: llvm/docs/LangRef.rst:9789
+   index type in a signed sense (``nsw``).
+*  The successive addition of offsets (without adding the base address) does
+   not wrap the pointer index type in a signed sense (``nsw``).
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jrtc27 wrote:
> nlopes wrote:
> > It's a bit stronger than that. The addition of each offset to the preceding pointer should not overflow. You can't do e.g.:
> > gep inbounds %p, -1, 1
> > 
> > because %p-1 is OOB, even though the result is in bounds (because %p must be in bounds).
> It's more nuanced than that, no? `%p` could be a pointer part-way through (or one past the end of) an object, in which case `%p-1` would still be in bounds?
This is specified in the next bullet point (successive addition to the base pointer must remain in bounds of the allocated object).


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  https://reviews.llvm.org/D90708/new/

https://reviews.llvm.org/D90708