I encountered some interesting performance differences in case of using release flag.

The code (test_d.d):
----------------------------8<--------------------------------
int main()
{
    const int arraySize = 30000;
    int[arraySize] myArray;
    for (int i = 0; i < arraySize; i++)
    {
        myArray[i] = i * i % 33;
    }
    for (int i = 0; i < arraySize; i++)
    {
        for (int j = i + 1; j < arraySize; j++)
        {
            myArray[(i+j)%arraySize] = (i + myArray[i] + myArray[j] * 17) % 33;
        }
    }
    return 0;
}
----------------------------8<--------------------------------

The tests I made:

$ dmd-1.00 test_d.d
gcc test_d.o -o test_d -m32 -lphobos -lpthread -lm -Xlinker -L/opt/dmd/1.00/lib

$ time ./test_d

real    0m21.365s
user    0m19.369s
sys     0m0.236s

$ dmd-1.00 -release test_d.d
gcc test_d.o -o test_d -m32 -lphobos -lpthread -lm -Xlinker -L/opt/dmd/1.00/lib

$ time ./test_d

real    0m29.500s
user    0m29.058s
sys     0m0.344s

$ dmd-1.00 -O test_d.d
gcc test_d.o -o test_d -m32 -lphobos -lpthread -lm -Xlinker -L/opt/dmd/1.00/lib

$ time ./test_d

real    0m17.109s
user    0m16.857s
sys     0m0.200s

$ dmd-1.00 -O -release test_d.d
gcc test_d.o -o test_d -m32 -lphobos -lpthread -lm -Xlinker -L/opt/dmd/1.00/lib

$ time ./test_d

real    0m28.653s
user    0m28.142s
sys     0m0.352s

Using the release flag I got dramatical worse performance. I also tested with dmd v0.173 and got the same results.