| Issue |
171777
|
| Summary |
LangRef: clarify semantics of `dereferenceable`
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
RalfJung
|
It is well-known, albeit unfortunately not documented in the LangRef, that `dereferenceable` on an argument means "this pointer must be dereferenceable for the entire duration of the function call".
But, what exactly does `dereferenceable` on the return type mean? [This example](https://llvm.godbolt.org/z/eTbMY5Gdx) by @nikic shows that apparently it does not just mean "`dereferenceable` here and now". But then what exactly is the scope for which that pointer is assumed to be dereferenceable? Is it the entire caller? That seems odd for two reasons:
- How can a function promise that its caller will keep the pointer dereferenceable? It has no way of knowing that...
- What about inlining? If this doesn't do anything special, it will extend the scope for which `dereferenceable` has to hold. To make that correct, basically `dereferenceable` would have to mean "dereferenceable for the entire rest of the program execution". Is that really the intent?
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