[BUG] benchmark::DoNotOptimize does not prevent a reference from being optimized away. about benchmark HOT 4 OPEN

IMHO in this particular case the

Compiler Explorer that works: https://godbolt.org/z/c3d5sc8s3

... is the case that actually does not work.
There is zero reason for the compiler to produce that load-and-spill there.

from benchmark.

From my user point of view, DoNotOptimize() means: do something with this lvalue such that it is a noop but the compiler will still think we are using it. So if you are using the value, the DoNotOptimize() is doing its job.

from benchmark.

That all said, this is your library so the semantics of using it is what you say. I was surprised by it. If that's known and expected then it is what it is.

from benchmark.

Right, but still, i don't quite see it.
A reference is a pointer, while an auto is a result of dereferencing that pointer.
If you drop DoNotOptimize from either snippet, there's a lot more changes,
so DoNotOptimize did prevent the argument from being optimized away.

from benchmark.