[llvm] r243996 - Avoid passing nullptr to std::equal.

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

> 
> On 2015-Aug-12, at 12:22, Yaron Keren <yaron.keren at gmail.com> wrote:
> 
> Better do it right on the first time. Some questions about llvm::equal :
> 
> 1) Would STLExtras be good place for llvm::equal ?

Yes, I think that's where I've seen stuff like this.

> 2) Should its contents be #ifdefed to _MSC_VER, something like
> 
>  template <class I1, class I2>
>     bool equal(I1 First1, I1 Last1, I2 First2) {
> #ifdef _MSC_VER
>       for (; First1 != Last1; ++First1, ++First2)
>         if (!(*First1 == *First2))
>           return false;
>       return true;
> #else
>      return std::equal(First1, Last1, First2);
> #endif
>     }

This SGTM (although I don't really know whether that's the right
macro to check).  This probably doesn't cover the case of using
a different STL when compiling with MSVC, but maybe that's not
important?

I'd probably add a couple of simple unit tests, too, and update
the CodingStandards to use `llvm::equal`.

> 3) Should it replace the other uses of std:;equal in LLVM and clang, although a nullptr is not possible in some (most?) of the code?

I'd say that's up to the MSVC folks (like you).  I wouldn't bother
for iterators that aren't nullable, but for the others, it seems
like it would be nice to have testcases to motivate the change?
Possibly better in follow-up commits.

At the least, it would be good to go back to the commits Hans
referenced in the next mail.