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What flag(s) do I need on the command line to disable the return-value optimisation automatically enabled by the g++ compiler?
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Named RVO GCC performs NRVO by default, but it can be disabled using the -fno-elide-constructors + compiler option. In contrast, MSVC disables NRVO by default, but it can be enabled using /O2 optimization+.
In the context of the C++ programming language, return value optimization (RVO) is a compiler optimization that involves eliminating the temporary object created to hold a function's return value. RVO is allowed to change the observable behaviour of the resulting program by the C++ standard.
> Note also that C doesn't have return-value-optimization, hence all your struct-returning functions will cause a call to memcpy (won't happen when compiled in C++ mode of course).
-fno-elide-constructors
The C++ standard allows an implementation to omit creating a temporary which is only used to initialize another object of the same type. Specifying this option disables that optimization, and forces G++ to call the copy constructor in all cases. [Source: man gcc]
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