4 ms·

I'm pretty sure it doesn't do this right now even in optimized builds: https://stackoverflow.com/a/38571602/11392896 https://stackoverflow.com/a/38571602/113928

• comex 5y ago
  LLVM has at least two optimizations that can elide moves in different circumstances, MemCpyOpt and SROA. But it depends on the situation. If you call a function that moves its argument to its return value, that move definitely won't get elided if the function is not inlined. But simple functions are likely to be inlined.
  • nextaccountic 5y ago
    > If you call a function that moves its argument to its return value, that move definitely won't get elided if the function is not inlined. Wow that's worse than I thought. This means that any pub function that does this pattern of taking ownership then giving it back should have at least #[inline] to enable inlining across crates, or maybe even #[inline(always)]. The difference to C to C++ is that in Rust, such pattern is sometimes necessary to work around the borrow checker.
• afranchuk 5y ago
  That answer is from 5.5 years ago. Rust was barely 1.0 then. A lot has changed in 5.5 years. See my godbolt link in the other reply for verification that it does optimize the moves away. Besides LLVM improvements, I suspect the moves might be optimized out at the MIR level, though that's just a hunch.