You can't just look at the codegen of the function itself, you also have to consider the metadata, and the overhead of processing any metadata Specifically her

You can't just look at the codegen of the function itself, you also have to consider the metadata, and the overhead of processing any metadata Specifically here (as I said in other comments) where it goes from complicated/quality of implementation issue to "shit this is complicated" is when you consider inlining. If noexcept inhibits inlining in any conceivable circumstances then it's having a dramatic (slightly indirect) impact on performance