IME "faster than C" without going into a lot of details what manual optimizations have gone into a specific piece of the C code doesn't mean much. Writing C code doesn't automatically give you high performance, but it gives you quite a bit of wiggle room to manually optimize the code.
In my mind, different languages have different "optimization sound barriers", where further manual optimization becomes impossible, or at least runs into diminishing returns. For instance Javascript can be made nearly as fast as "vanilla" natively compiled C code, but that means writing asm.js by hand, which is entirely different from "idiomatic Javascript". It's not worth it writing asm.js by hand, when C compiled to asm.js (or WASM nowadays) is much more maintainable.
Same with garbage-collected languages in general. You can write fast code with very little overhead from the garbage collector, but this means you need to know exactly how the garbage collector of that language works, and the resulting code will usually look very different and will be harder to maintain than the idiomatic style of that language.
In standard C the optimization sound barrier is a bit further away than in many other high-level languages but it's not all that special, on the other hand C with compiler- and CPU-architecture-specific extensions is pretty good (e.g. extensions can push the sound barrier quite a bit further away).
In my mind, different languages have different "optimization sound barriers", where further manual optimization becomes impossible, or at least runs into diminishing returns. For instance Javascript can be made nearly as fast as "vanilla" natively compiled C code, but that means writing asm.js by hand, which is entirely different from "idiomatic Javascript". It's not worth it writing asm.js by hand, when C compiled to asm.js (or WASM nowadays) is much more maintainable.
Same with garbage-collected languages in general. You can write fast code with very little overhead from the garbage collector, but this means you need to know exactly how the garbage collector of that language works, and the resulting code will usually look very different and will be harder to maintain than the idiomatic style of that language.
In standard C the optimization sound barrier is a bit further away than in many other high-level languages but it's not all that special, on the other hand C with compiler- and CPU-architecture-specific extensions is pretty good (e.g. extensions can push the sound barrier quite a bit further away).
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