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

[Duncan P. N. Exon Smith]

> 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?  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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