More on semantics of opPow: return type

[Bill Baxter]

On Mon, Dec 7, 2009 at 2:29 PM, bearophile <bearophileHUGS at lycos.com> wrote:
> Lars T. Kyllingstad:
>> I also seem to remember someone (was it Don or bearophile, perhaps?)
>> listing various optimisation possibilities that are more readily
>> available if ^^ is a built-in operator.
>
> It was Don, I think.
> Those optimizations can be done with the pow, ipow and cpow (real, integer, complex, this is just an idea) functions too. GCC for example simplifies cases when the exponent is 2 or 3 (that are the most common):
>
> // C code
> #include "stdio.h"
> #include "math.h"
> #include "stdlib.h"
>
> int main() {
>    int x = atoi("100");
>    printf("%f\n", pow(x, 2));
>    return 0;
> }
>
> Compiled with:
> gcc version 4.3.3-dw2-tdm-1 (GCC)
> gcc -Wall -S -O3 test2.c -o test2.s
>
>    ...
>    call    _atoi
>    pushl   %eax
>    fildl   (%esp)
>    addl    $4, %esp
>    fmul    %st(0), %st
>    movl    $LC1, (%esp)
>    fstpl   4(%esp)
>    call    _printf
>    ...
>
> Some weeks ago I have filed a bug asking for a similar optimization in LLVM too (so LDC too will have it).

Holy smokes!  You actually file bugs in the LLVM database?!

--bb