Inherent code performance advantages of D over C?

[deadalnix]

On Friday, 6 December 2013 at 22:20:19 UTC, Walter Bright wrote:
>
> "there is no way proper C code can be slower than those 
> languages."
>
>   -- 
> http://www.reddit.com/r/programming/comments/1s5ze3/benchmarking_d_vs_go_vs_erlang_vs_c_for_mqtt/cduwwoy
>
> comes up now and then. I think it's incorrect, D has many 
> inherent advantages in generating code over C:
>
> 1. D knows when data is immutable. C has to always make worst 
> case assumptions, and assume indirectly accessed data mutates.
>
> 2. D knows when functions are pure. C has to make worst case 
> assumptions.
>
> 3. Function inlining has generally been shown to be of 
> tremendous value in optimization. D has access to all the 
> source code in the program, or at least as much as you're 
> willing to show it, and can inline across modules. C cannot 
> inline functions unless they appear in the same module or in .h 
> files. It's a rare practice to push many functions into .h 
> files. Of course, there are now linkers that can do whole 
> program optimization for C, but those are kind of herculean 
> efforts to work around that C limitation of being able to see 
> only one module at a time.
>
> 4. C strings are 0-terminated, D strings have a length 
> property. The former has major negative performance 
> consequences:
>
>     a. lots of strlen()'s are necessary
>
>     b. using substrings usually requires a malloc/copy/free 
> sequence
>
> 5. CTFE can push a lot of computation to compile time rather 
> than run time. This has had spectacular positive performance 
> consequences for things like regex. C has no CTFE ability.
>
> 6. D's array slicing coupled with GC means that many 
> malloc/copy/free's normally done in C are unnecessary in D.
>
> 7. D's "final switch" enables more efficient switch code 
> generation, because the default doesn't have to be considered.

You can add generic programming.