Hi Michael,

> On Mar 18, 2019, at 2:35 PM, Michael Catanzaro <mcatanz...@igalia.com> wrote:
> 
> Hi,
> 
> GCC 9 has new -Wpessimizing-move ("warning: moving a local object in a return 
> statement prevents copy elision") and -Wredundant-move ("warning: redundant 
> move in return statement") warnings. These are enabled by -Wextra (which we 
> use) and will be triggered by code like:
> 
> return WTFMove(foo);
> 
> when foo is a copyable type. This idiom is only appropriate if foo is a 
> noncopyable (move-only) type. We have many, many instances of such code. I'm 
> trying to fix them. Please don't add more! (It's easy enough to disable the 
> warnings, but they're there for a reason.)

It might not even be appropriate for move-only types because of NRVO.

FWIW, Apple’s ports use the equivalent clang warning for pessimizing and 
redundant moves, and we cleaned up a bunch of these mistakes in our ports a few 
years ago. Hopefully you aren’t finding any of these mistakes in shared code.

(WTFMove was written to accommodate these warnings, in fact.)

Really glad you’re turning these warnings on!

Andy
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