[llvm] r215986 - ADT: Avoid using std::equal in ArrayRef::equals

[David Blaikie]

On Tue, Aug 19, 2014 at 12:30 PM, Duncan P. N. Exon Smith
<dexonsmith at apple.com> wrote:
>
>> On 2014-Aug-19, at 11:04, David Blaikie <dblaikie at gmail.com> wrote:
>>
>> On Tue, Aug 19, 2014 at 11:04 AM, David Blaikie <dblaikie at gmail.com> wrote:
>>> On Tue, Aug 19, 2014 at 9:36 AM, Duncan P. N. Exon Smith
>>> <dexonsmith at apple.com> wrote:
>>>> Author: dexonsmith
>>>> Date: Tue Aug 19 11:36:21 2014
>>>> New Revision: 215986
>>>>
>>>> URL: http://llvm.org/viewvc/llvm-project?rev=215986&view=rev
>>>> Log:
>>>> ADT: Avoid using std::equal in ArrayRef::equals
>>>>
>>>> MSVC's STL has a bug in `std::equal()`: it asserts on nullptr iterators,
>>>> causing a block revert in r215981.  This works around that by re-writing
>>>> `ArrayRef::equals()` to do the work itself.
>>>
>>> Adding a comment might be nice, describing what we're working around,
>>> so we can switch it back later?
>
> Was the comment in this commit not clear enough?

Oh, it was clear enough, I was just bad at reading - don't mind me.

- David

> What do you think
> would be better?
>
>> Oh, and you could add a unit test, if you like.
>
> r216008.  Thanks!
>
>>
>>>
>>>>
>>>> Modified:
>>>>    llvm/trunk/include/llvm/ADT/ArrayRef.h
>>>>
>>>> Modified: llvm/trunk/include/llvm/ADT/ArrayRef.h
>>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/ArrayRef.h?rev=215986&r1=215985&r2=215986&view=diff
>>>> ==============================================================================
>>>> --- llvm/trunk/include/llvm/ADT/ArrayRef.h (original)
>>>> +++ llvm/trunk/include/llvm/ADT/ArrayRef.h Tue Aug 19 11:36:21 2014
>>>> @@ -145,7 +145,13 @@ namespace llvm {
>>>>     bool equals(ArrayRef RHS) const {
>>>>       if (Length != RHS.Length)
>>>>         return false;
>>>> -      return std::equal(begin(), end(), RHS.begin());
>>>> +      // Don't use std::equal(), since it asserts in MSVC on nullptr iterators.
>>>> +      for (auto L = begin(), LE = end(), R = RHS.begin(); L != LE; ++L, ++R)
>>>> +        // Match std::equal() in using == (instead of !=) to minimize API
>>>> +        // requirements of ArrayRef'ed types.
>>>> +        if (!(*L == *R))
>>>> +          return false;
>>>> +      return true;
>>>>     }
>>>>
>>>>     /// slice(n) - Chop off the first N elements of the array.
>>>>
>>>>
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>