Inherent code performance advantages of D over C?

[Sean Kelly]

On Wednesday, 11 December 2013 at 00:19:50 UTC, H. S. Teoh wrote:
> On Tue, Dec 10, 2013 at 11:47:47PM +0100, Sean Kelly wrote:
>> 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."
>> 
>> Didn't Bjarne cover this in his C++ performance talk at SD 
>> West in
>> 2007?  Templates alone can make C++ and D code faster than even
>> hand-optimized C.  And that doesn't even consider some of the 
>> other
>> points you mentioned.
>
> The thing is, what constitutes "proper C" is not well-defined, 
> because
> since C translates to machine code (as does C++ and D), in 
> theory
> *everything* has access to the same level of performance -- 
> that is, the
> hardware. So arguably, no matter what code fragment you may 
> present in C++ or D, there's always a corresponding C code 
> fragment that performs equally fast or faster. But that 
> obscures the fact that said C code fragment may be written in 
> an unmanageably convoluted style that no one in their right 
> mind would actually use in practice. (And the same can be said 
> for C++ and D: use asm blocks, and you'll beat any "normal" C 
> code, but that proves nothing since the whole issue is writing 
> *idiomatic* C vs. *idiomatic* D, not writing things in an 
> unnatural way just so you can lay claim to the title of best 
> performance.)

Bjarne's point was essentially that templates allow code to be 
inlined to a ridiculous degree.  C code simply can't compete with 
that and still be maintainable.  I suppose you could expand that 
to mean any inlineable code rather than just templates, but the 
same assertion holds.

I don't think it makes sense to consider the scenario where the 
"C code" is purpose built assembly code because that says nothing 
about the language itself.  Nor does it make sense to restrict 
the compared language to "C style code" (whatever that means) 
because any speed advantages would be leveraging language 
features or conventions not present in idiomatic C.

For example, I've posted benchmarks of a JSON parser here before 
that I wrote in C and it's considerably faster than anything I've 
seen done in D.  Does that mean that C is faster than D?  
Absolutely not.  I could recompile the same code in D and have it 
be just as fast as the C version.  The more interesting issue is 
how easy that problem was to solve in each language, and which is 
more maintainable.