[PATCH] D77621: ADT: SmallVector size/capacity use word-size integers when elements are small

[Nikita Popov via Phabricator via cfe-commits]

nikic added inline comments.


================
Comment at: llvm/include/llvm/ADT/SmallVector.h:84
 
+template <class Size_T> const size_t SmallVectorBase<Size_T>::SizeTypeMax;
+
----------------
dblaikie wrote:
> nikic wrote:
> > Is this needed? I don't think it makes a lot of sense to allow odr-use of `SizeTypeMax`. As it's a protected member, it's only used in the SmallVector implementation, where we control how it is used.
> It's used as a parameter to std::min, so it's already odr used & I'd rather not leave it as a trap to walk around even if we addressed that issue.
> 
> I assume if it were a constexpr local in a protected inline function it wouldn't hinder optimizations in any real way?
> It's used as a parameter to std::min, so it's already odr used & I'd rather not leave it as a trap to walk around even if we addressed that issue.

Oh, right you are! In that case this seems fine :)

> I assume if it were a constexpr local in a protected inline function it wouldn't hinder optimizations in any real way?

The change from constexpr function to constexpr static didn't change anything performance-wise, so either way works for me.

Another option is:

```
enum : size_t { SizeTypeMax = std::numeric_limits<Size_T>::max() };
```

Kind of sad that in C++14, using an enum is still the only "no nonsense" way to declare a constant.


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  https://reviews.llvm.org/D77621/new/

https://reviews.llvm.org/D77621