[cmpitg]

I don't think it has anything to do the relationship between the language and its (compiler/interpreter) performance. Besides, the subset of a large number or programming language could be considered bare metal, right? If so, why mentioning bare metal at all?

[xamuel]

Most things you do in a language like C, have direct counterparts in the physical machine. If you get into stuff like game hacking, you can literally "see" these things through whatever RAM-hacking tool you're using.

Dereference a pointer? That translates to a tiny fragment of machine code for "dereference pointer".

Create a lambda? That translates to a big blob of machine code for "set up this bunch of paperwork that will be used to painstakingly emulate a lambda".

[cmpitg]

And what does it have anything to do with C++ compared to any other language X? The bare-metal characteristics could be created as a subset of any non-safe non-garbage-collected language.

[xamuel]

You're right. I think someone else already pointed out asm.js as a good example.

Of course, it won't happen magically: someone has to go to the effort of defining the subset and building the compiler for it.

You can't expect the general-purpose compiler to automatically be as optimal as possible just because a program happens to use the subset. For example, the program might be being compiled into something like a java .class file meant for importing to a less conservative calling program. This would be incompatible with putting those bare metal optimizations in the .class file.