On 8 April 2013 13:25, Jacob Carlborg <doob@me.com> wrote:

On 2013-04-08 10:29, Iain Buclaw wrote:

This information could possibly be helpful. Though given that most of
(gdc) codegen is on par with g++, there's probably not much on the list
that isn't already detected by the backend optimisation passes.

Multiple calls to pure functions could be cached.

--
/Jacob Carlborg

Not always, but in some circumstances, yes.

---
struct Foo
{
int a = 0;
pure int bar (immutable int x)
{
++a;
return x * 2;
}
}

void main()
{
Foo f;
int i = f.bar(2) + f.bar(2);

assert (i == 8);
assert (f.a == 2);
}
---

Again, the characteristics of D pure functions mean that the backend can const-fold away the function entirely under normal optimisations.

---
D main ()
{
<bb 2>:
# DEBUG f.a => 0
# DEBUG f.a => 1
# DEBUG f.a => 2
# DEBUG i => 8
return 0;
}
---

Possibly strongly-pure functions could be marked as pure in the 'C' sense, but only if they are also nothrow, eg to add to the above example:

---
pure nothrow int baz (Foo f)
{
return f.bar(2) + f.bar(2);
}
---

Regards

--
Iain Buclaw

*(p < e ? p++ : p) = (c & 0x0f) + '0';