[PATCH] D100672: [ADT] Add new type traits for type pack indexes

Tue Jun 29 13:34:48 PDT 2021

scott.linder added a comment.

In D100672#2767612 <https://reviews.llvm.org/D100672#2767612>, @dblaikie wrote:

> In D100672#2766442 <https://reviews.llvm.org/D100672#2766442>, @scott.linder wrote:
>
>> This seems like a bug in parameter pack expansion in older versions of MSVC, compare 19.10 https://godbolt.org/z/TMd3K8WoK with 19.14 https://godbolt.org/z/9c9TT8bnb
>>
>> @stella.stamenova is there any possibility the build bots could be updated to the latest MSVC 2017 update? https://llvm.org/docs/GettingStartedVS.html#software says "Visual Studio 2017 or higher, with the latest Update installed", but I could also see us wanting to support any VS 2017 release if possible.
>>
>> If we want to support all updates of VS 2017 I can just substitute in the old definition of `llvm::TypeIndex` in place of the new `llvm::FirstIndexOfType`, but I might have to think more about how to work around this in `llvm::TypesAreDistinct`
>
> I'd generally be happy to stick with the original requirement. @stella.stamenova - any chance you could update the bot(s) here?

Would you mind taking a look at the current diff and seeing if it is acceptable? I am fairly confident this will work with any reasonably modern MSVC, and I don't think there is a substantial hit to readability. There may be some compile-time performance cost, but I don't know how to quantify it.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D100672/new/

https://reviews.llvm.org/D100672