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Make note of noalias in unsafe reference section #23813

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Mar 31, 2015
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Make note of noalias in unsafe reference section #23813

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7 changes: 6 additions & 1 deletion src/doc/reference.md
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Expand Up @@ -1231,12 +1231,15 @@ the guarantee that these issues are never caused by safe code.

* Data races
* Dereferencing a null/dangling raw pointer
* Mutating an immutable value/reference without `UnsafeCell`
* Reads of [undef](http://llvm.org/docs/LangRef.html#undefined-values)
(uninitialized) memory
* Breaking the [pointer aliasing
rules](http://llvm.org/docs/LangRef.html#pointer-aliasing-rules)
with raw pointers (a subset of the rules used by C)
* `&mut` and `&` follow LLVM’s scoped [noalias] model, except if the `&T`
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There's a point just above talking about UnsafeCell, maybe these could be merged/moved closer together?

contains an `UnsafeCell<U>`. Unsafe code must not violate these aliasing
guarantees.
* Mutating an immutable value/reference without `UnsafeCell<U>`
* Invoking undefined behavior via compiler intrinsics:
* Indexing outside of the bounds of an object with `std::ptr::offset`
(`offset` intrinsic), with
Expand All @@ -1253,6 +1256,8 @@ the guarantee that these issues are never caused by safe code.
code. Rust's failure system is not compatible with exception handling in
other languages. Unwinding must be caught and handled at FFI boundaries.

[noalias]: http://llvm.org/docs/LangRef.html#noalias

##### Behaviour not considered unsafe

This is a list of behaviour not considered *unsafe* in Rust terms, but that may
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