stride in slices

[DigitalDesigns]

On Tuesday, 5 June 2018 at 20:07:06 UTC, Ethan wrote:
> On Tuesday, 5 June 2018 at 19:05:27 UTC, DigitalDesigns wrote:
>> For loops HAVE a direct cpu semantic! Do you doubt this?
>
> ...
>
> Right. If you're gonna keep running your mouth off. How about 
> looking at some disassembly then.
>
> for(auto i=0; i<a.length; i+=strideAmount)
>
> Using ldc -O4 -release for x86_64 processors, the initialiser 
> translates to:
>
> mov byte ptr [rbp + rcx], 0
>
> The comparison translates to:
>
> cmp r13, rcx
> ja .LBB0_2
>
> And the increment and store translates to:
>
> mov byte ptr [rbp + rcx], 0
> movsxd rcx, eax
> add eax, 3
>
> So. It uses three of the most basic instructions you can think 
> of: mov, cmp, j<cond>, add.
>
> Now, what might you ask are the instructions that a range 
> compiles down to when everything is properly inlined?
>
> The initialisation, since it's a function, pulls from the stack.
>
> mov rax, qword ptr [rsp + 16]
> movsxd rcx, dword ptr [rsp + 32]
>
> But the comparison looks virtually identical.
>
> cmp rax, rcx
> jb .LBB2_4
>
> But how does it do the add? With some register magic.
>
> movsxd rcx, edx
> lea edx, [rcx + r9]
>
> Now, what that looks like it's doing to me is combing the 
> pointer load and index increment in to two those two 
> instructions. One instruction less than the flat for loop.
>
> In conclusion. The semantics you talk about are literally some 
> of the most basic instructions in computing; and that escaping 
> the confines of a for loop for a foreach loop can let the 
> compiler generate more efficient code than 50-year-old compsci 
> concepts can.

Ok asshat! You still don't get it! I didn't say ranges would not 
compile down to the same thing! Do you have trouble understanding 
the English language?

You don't seem to get the concept where ranges are library 
solutions and someone can some along at any time and modify some 
code and WHAM! They no longer compile down to your efficient 
precious instructions. That is far more unlikely to occur with 
language semantics. Why is that so difficult for you to 
understand you sure do you have an attitude for someone that has 
difficulty with English.