Major performance problem with std.array.front()

[Kagamin]

On Friday, 7 March 2014 at 04:01:15 UTC, Adam D. Ruppe wrote:
> BTW you know what would help this? A pragma we can attach to a 
> struct which makes it a very thin value type.
>
> pragma(thin_struct)
> struct A {
>    int a;
>    int foo() { return a; }
>    static A get() { A(10); }
> }
>
> void test() {
>     A a = A.get();
>     printf("%d", a.foo());
> }
>
> With the pragma, A would be completely indistinguishable from 
> int in all ways.
>
> What do I mean?
> $ dmd -release -O -inline test56 -c
>
> Let's look at A.foo:
>
> A.foo:
>    0:   55                      push   ebp
>    1:   8b ec                   mov    ebp,esp
>    3:   50                      push   eax
>    4:   8b 00                   mov    eax,DWORD PTR [eax] ; 
> waste!
>    6:   8b e5                   mov    esp,ebp
>    8:   5d                      pop    ebp
>    9:   c3                      ret
>
>
> It is line four that bugs me: the struct is passed as a 
> *pointer*, but its only contents are an int, which could just 
> as well be passed as a value. Let's compare it to an identical 
> function in operation:
>
> int identity(int a) { return a; }
>
> 00000000 <_D6test568identityFiZi>:
>    0:   55                      push   ebp
>    1:   8b ec                   mov    ebp,esp
>    3:   83 ec 04                sub    esp,0x4
>    6:   c9                      leave
>    7:   c3                      ret
>
> lol it *still* wastes time, setting up a stack frame for 
> nothing. But we could just as well write asm { naked; ret; } 
> and it would work as expected: the argument is passed in EAX 
> and the return value is expected in EAX. The function doesn't 
> actually have to do anything.

struct A {
    int a;
    //int foo() { return a; }
    static A get() { A(10); }
}

int foo(A a) { return a.a; }

printf("%d", a.foo());

Now it's passed by value.

Though, I needed checked arithmetic only twice: for cast from 
long to int and for cast from double to long. If you expect your 
number type to overflow, you probably chose wrong type.