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

[Nuno Lopes via Phabricator via llvm-commits]

nlopes 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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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.


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Comment at: llvm/docs/LangRef.rst:9785
+   itself.
+*  If the type of an index is larger than than the pointer index type, the
+   truncation to the pointer index type preserves the signed value.
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than than


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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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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).


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

https://reviews.llvm.org/D90708