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

[David Blaikie]

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?

Oh, and you could add a unit test, if you like.

>
>>
>> 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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