Update MSVC version number in preprocessor check

[nealsid]

Summary

Passing template parameter packs to std::map doesn't work in VS 2017/2019, so this updates the preprocessor version check to use an alternate version in VS2019, as well.

[DavidSpickett]

Checking https://docs.microsoft.com/en-us/cpp/preprocessor/predefined-macros?view=msvc-160 this LGTM.

I can land this for you, but it would also make a good test commit once you have access. Let me know.

[nealsid]

Whoops, I did not realize my VS was out of date - appreciate the link. Let me try building with the latest updates, perhaps a later version works.

Re: Testing committing this with commit access would be great, thank you.

[nealsid]

Ah, my Windows Boot Camp partition seems to have bit it, so it may be a couple days before I can test & update this, sorry. Please hold off.

[nealsid]

Sorry, this got a little complicated. On my previous install I had VS 2019 16.5, which ran into the compile error. When I reinstalled, 16.0, 16.6, and 16.9 worked, but 16.4/16.5 did not. Sounds like a super tiny regression for only 2 minor updates. As far as the actual issue, I could not fully understand it, but it seems to have something to do with applying parameter pack arguments while also using default values for std::map template parameters.

For the actual patch, we could:

• Leave the version number check at 1926 and update the comment to mention 16.4/16.5 not building is known.
• Update the preprocessor check to version >= 1920 (which is VS2019 16.0) and != 1924/1925 (16.4/16.5). I'm guessing most people are upgraded past 16.4/16.5 though, so a preprocessor check for those versions may not be used all that much in practice...and would probably hang around the code base forever ;).

Thanks,

Neal

[DavidSpickett]

Leave the version number check at 1926 and update the comment to mention 16.4/16.5 not building is known.

I'd do that. If a few versions get the #else version when they could use the first version, it's not going to change much.

[DavidSpickett]

LGTM

[nealsid]

Awesome. If you or someone could land it for me, that would be appreciated. Thanks!

llvm/lib/Target/Hexagon/HexagonVectorCombine.cpp

 }
 template <> LoadInst *isCandidate<LoadInst>(Instruction *In) {
   return getIfUnordered(dyn_cast<LoadInst>(In));
 }
 template <> StoreInst *isCandidate<StoreInst>(Instruction *In) {
   return getIfUnordered(dyn_cast<StoreInst>(In));
 }
 
-#if !defined(_MSC_VER) || _MSC_VER >= 1924
-// VS2017 has trouble compiling this:
+#if !defined(_MSC_VER) || _MSC_VER >= 1926
+// VS2017 and some versions of VS2019 have trouble compiling this:
 // error C2976: 'std::map': too few template arguments
+// VS 2019 16.x is known to work, except for 16.4/16.5 (MSC_VER 1924/1925)
 template <typename Pred, typename... Ts>
 void erase_if(std::map<Ts...> &map, Pred p)
 #else
 template <typename Pred, typename T, typename U>
 void erase_if(std::map<T, U> &map, Pred p)
 #endif
 {
   for (auto i = map.begin(), e = map.end(); i != e;) {