On Friday, 24 April 2015 at 13:55:49 UTC, Steven Schveighoffer
wrote:
On 4/24/15 9:13 AM, Chris wrote:
On Friday, 24 April 2015 at 11:53:56 UTC, Marc Schütz wrote:
Most of the time is taken up by the array's allocation. The
optimizers
of both DMD and LDC evidently doesn't optimize it away when
you use
`ref`, even though it could in theory.
Remove the `enum` and just use a normal global variable, and
you will
get more or less identical times for all three loops. LDC
even turns
then into empty functions (didn't check for DMD).
I've tried it, and the loops indeed show similar results. What
is it
about `enum` that slows it down?
enum of an array literal is like pasting the array literal
wherever the enum lives.
So for example, your const loop:
void constLoop() {
size_t cnt;
foreach (const ref w; words)
cnt += w.length;
}
Is really like saying:
void constLoop() {
size_t cnt;
foreach (const ref w; ["Hello", "world", "Ola", "mundo"])
cnt += w.length;
}
And note that in D right now, an array literal is NOT stored in
the data segment. It's generated every time you use it (with a
call to _d_newarray, which allocates on the GC).
There was a push a while back to make array literals immutable
and placed in the data segment. But it never panned out, would
break too much code.
-Steve
Thanks for the clarification.
