Reduce has dreadful performance?

[Laeeth Isharc via Digitalmars-d]

On Thursday, 18 June 2015 at 10:34:46 UTC, Laeeth Isharc wrote:
> On Thursday, 18 June 2015 at 10:27:58 UTC, Russel Winder wrote:
>> On a given machine, the code:
>>
>> double sequential_loop(const int n, const double delta) {
>>   auto sum = 0.0;
>>   foreach (immutable i; 1 .. n + 1) {
>>     immutable x = (i - 0.5) * delta;
>>     sum += 1.0 / (1.0 + x * x);
>>   }
>>   return 4.0 * delta * sum;
>> }
>>
>> runs in about 6.70s. However the code:
>>
>> double sequential_reduce(const int n, const double delta) {
>>   return 4.0 * delta * reduce!((double t, int i){immutable x = 
>> (i -
>> 0.5) * delta; return t + 1.0 / (1.0 + x * x);})(0.0, iota(1, n 
>> + 1));
>> }
>>
>> runs in about 17.03s, whilst:
>>
>> double sequential_reduce_alt(const int n, const double delta) {
>>   return 4.0 * delta * reduce!"a + b"(
>>          map!((int i){immutable x = (i - 0.5) * delta; return 
>> 1.0 /
>> (1.0 + x * x);})(iota(1, n + 1)));
>> }
>>
>> takes about 28.02s. Unless I am missing something (very 
>> possible), this
>> is not going to create a good advert for D as an imperative 
>> language
>> with declarative (internal iteration) expression.
>
> which compiler ?

fwiw n=1bn, delta=0.1
ldc no params:
8.749s/17.466s
ldc -O2
4.541s/4.562s
gdc no params
4.690/22.163 (!)
gdc -O2
4.552/4.551