[cfe-commits] [PATCH] Fix for reinterpret_cast (bug 11747)

[Aaron Ballman]

On Thu, Jan 19, 2012 at 12:00 AM, Eli Friedman <eli.friedman at gmail.com> wrote:
> On Mon, Jan 16, 2012 at 8:38 PM, Aaron Ballman <aaron at aaronballman.com> wrote:
>> On Sun, Jan 15, 2012 at 9:05 PM, Eli Friedman <eli.friedman at gmail.com> wrote:
>>> On Sun, Jan 15, 2012 at 1:45 PM, Aaron Ballman <aaron at aaronballman.com> wrote:
>>>> This is a patch for fixing 11747, allowing reinterpret_cast to "cast"
>>>> where the source and destination types are the same as per
>>>> [expr.reinterpret.cast]p2.  The fix itself is fairly simple -- the
>>>> code was already there, it just needed to be moved up slightly since
>>>> the previous check was for source and dest being pointers.
>>>
>>> C++11 [expr.reinterpret.cast]p2 is as follows:
>>>
>>> The reinterpret_cast operator shall not cast away constness (5.2.11).
>>> An expression of integral, enumeration, pointer, or pointer-to-member
>>> type can be explicitly converted to its own type; such a cast yields
>>> the value of its operand.
>>
>> Attached is a new patch to hopefully better address this, as well as
>> some additional test cases.
>
> +    // C++ 5.2.10p2 has a note that mentions that, subject to all other
> +    // restrictions, a cast to the same type is allowed so long as it does not
> +    // cast away constness. The intent is not entirely clear here, since all
> +    // other paragraphs explicitly forbid casts to the same type.
> +    //
> +    // The only allowed types are: integral, enumeration, pointer, or
> +    // pointer-to-member types.
>
> This comment is really unclear... you should really explicitly state
> that the C++98 version is unclear, and C++11 clarifies this case.

I've clarified now, thanks for pointing out the confusion!

> +    } else if (SrcType->isPointerType() ||
> +      SrcType->isMemberPointerType()) {
>
> The original code allowed "DestType->isAnyPointerType() ||
> DestType->isBlockPointerType()".  I don't see any reason to restrict
> Objective-C or block pointers.

Nor do I, I've added this in as well.

> +      if (CastsAwayConstness(Self, SrcType, DestType, /*CheckCVR=*/!CStyle,
> +                           /*CheckObjCLifetime=*/CStyle)) {
>
> How could a cast where the source and destination types are identical
> cast away constness?

>From my testing, the equality test does not take cv qualifiers into
account.  Is there another way I should be testing for equality that
does?

I've attached a revised patch based on the changes described here.

~Aaron
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