[llvm] r252380 - Reapply "ADT: Require explicit ilist iterator/pointer conversions"

[Duncan P. N. Exon Smith via llvm-commits]

> On 2015-Nov-06, at 16:59, Duncan P. N. Exon Smith via llvm-commits <llvm-commits at lists.llvm.org> wrote:
> 
> Author: dexonsmith
> Date: Fri Nov  6 18:59:29 2015
> New Revision: 252380
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=252380&view=rev
> Log:
> Reapply "ADT: Require explicit ilist iterator/pointer conversions"
> 
> This reverts commit r252373, reapplying r252372 now that I've updated
> clang-tools-extra.

Unless I revert, this will have be my last commit of the day, as I
apparently can't correctly check my commit messages :/.  The broken
builds were in the LLVM examples directory and LLDB.

>  Original commit message follows.
> 
> ADT: Require explicit ilist iterator/pointer conversions
> 
> Disallow implicit conversions between ilist iterators and element
> points.  Explicit conversions still work of course.
> 
> This is the first step toward removing the undefined behaviour in
> `ilist` and `iplist`:
> http://lists.llvm.org/pipermail/llvm-dev/2015-October/091115.html
> 
> The motivation for removing the implicit iterators is that I came across
> real bugs (that were *really* getting lucky).  More details and some
> brief discussion later in that thread:
> http://lists.llvm.org/pipermail/llvm-dev/2015-October/091617.html
> 
> Note: if you have out-of-tree code, it should be fairly easy to revert
> this patch downstream while you update your out-of-tree call sites.
> Note that these conversions are occasionally latent bugs (that may
> happen to "work" now, but only because of getting lucky with UB;
> follow-ups will change your luck).  When they are valid, I suggest using
> `->getIterator()` to go from pointer to iterator, and `&*` to go from
> iterator to pointer.
> 
> Modified:
>    llvm/trunk/include/llvm/ADT/ilist.h
> 
> Modified: llvm/trunk/include/llvm/ADT/ilist.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/ilist.h?rev=252380&r1=252379&r2=252380&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/ADT/ilist.h (original)
> +++ llvm/trunk/include/llvm/ADT/ilist.h Fri Nov  6 18:59:29 2015
> @@ -220,8 +220,8 @@ private:
>   template<class T> void operator-(T) const;
> public:
> 
> -  ilist_iterator(pointer NP) : NodePtr(NP) {}
> -  ilist_iterator(reference NR) : NodePtr(&NR) {}
> +  explicit ilist_iterator(pointer NP) : NodePtr(NP) {}
> +  explicit ilist_iterator(reference NR) : NodePtr(&NR) {}
>   ilist_iterator() : NodePtr(nullptr) {}
> 
>   // This is templated so that we can allow constructing a const iterator from
> @@ -241,7 +241,7 @@ public:
>   void reset(pointer NP) { NodePtr = NP; }
> 
>   // Accessors...
> -  operator pointer() const {
> +  explicit operator pointer() const {
>     return NodePtr;
>   }
> 
> 
> 
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