[PATCH] D115208: [NFC][MachineInstr] No need to std::move the DebugLoc

[David Blaikie via Phabricator via llvm-commits]

dblaikie added a comment.

I /think/ given that `DebugLoc` has a `TrackingMDNodeRef` member, which has a `TrackingMDRef` member which has cheaper move than copy, then DebugLoc /probably/ should be passed by value when a copy is going to be made - since it means callers can pass by lvalue or rvalue and get move opportunities when possible.

Given this API scenario:

  CheapToMove Dest;
  void Caller() {
    CheapToMove Source;
    Intermediate(Source); // 1 
    Intermediate(CheapToMove()); //2
  }
  void Implementation(/* What Type Goes here? */ CTM) {
    Dest = std::move(CTM); // move is a no-op here if CTM hapens to be a const ref
  }

If the type is const ref, then (1) produces a single copy and (2) produces a single copy.
If the type is by-value, then (1) produces a move and a copy (worse by a copy, that should be cheap), and (2) produces 2 moves (better for cheaply movable things).

Does that make sense?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D115208/new/

https://reviews.llvm.org/D115208