Fixups for UnsafePointer documentation #5994
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Don't forget "just-past-the-end" pointers, which (like in C) are also valid. |
added 3 commits
November 30, 2016 18:35
Offsets lower to GetElementPointer inbounds, which specifies that it's Undefined Behaviour for the result to be out of bounds, regardless of if the result is actually dereferenced.
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@jrose-apple I didn't forget them, I was just hoping everyone in the world would assume this is included in the definition of in-bounds. I have a feeling the "correct" solution involves all of these preconditions linking to a definition, but I'm not sure where that would go. |
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@swift-ci please smoke test |
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Looks fine to me. |
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TIL about poison values. LGTM! Going to merge so I can integrate these changes into some other revisions. |
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Two minor fixups, and one big/scary documentation change.
Until now we've failed to document the Undefined Behaviour requirements on pointer offsets. In particular we lower these operations to LLVM's
GetElementPointer inbounds: http://llvm.org/docs/LangRef.html#id214In order to avoid getting into the nitty gritty details of poison, I just specified staying in bounds of the current allocation is a precondition. I am very far from certain that this is the ideal wording, and we should discuss the best wording (and how much Swift wants to inherit from llvm here).