[PATCH] D73675: Avoid many std::tie/tuple instantiations in ASTImporter

[Arthur O'Dwyer via Phabricator via cfe-commits]

Quuxplusone added inline comments.


================
Comment at: clang/lib/AST/ASTImporter.cpp:1152
+  if (Error E = importSeq(ToElementType, ToSizeExpr))
+    return std::move(E);
 
----------------
martong wrote:
> Quuxplusone wrote:
> > As the author of [P1155 "More Implicit Move"](https://wg21.link/p1155), I would expect that you don't need `return std::move(E)` — `return E` should just as well perform "implicit move" in C++11 and later, assuming that `llvm::Expected<QualType>` has a valid constructor from `llvm::Error&&`.
> > 
> > You're not seeing any compiler diagnostic that //suggests// you use `std::move` here, are you?
> I have some vague and obscure memory about that GCC 4.8 (or 5.2) required explicitly the && cast, otherwise we had a diagnostic (@gamesh411 maybe you help me to recall that?)
Ah, you are absolutely correct: GCC 4.9.4 does not do implicit move in this situation, whereas GCC 5.1 and later do do it.
https://godbolt.org/z/YDHtTH
I didn't realize that portability back to GCC 4.9 was still a concern for LLVM/Clang. If it is, then please feel free to keep the `std::move` here and throughout (but maybe mention it in the commit message for the benefit of others who might think as I did).  If portability back to pre-GCC-5 is //not// a concern, then I would continue to recommend removing the `std::move`.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D73675/new/

https://reviews.llvm.org/D73675