If Zortech C++ and dmc++ are fast, why is dmd's asm slow?

[James Lu]

> In 1988 Zortech C++ was the first C++ compiler to ship for 
> Windows and the performance of its compiled executables 
> compared favourably against Microsoft C 5.1 and Watcom C 6.5 in 
> a graphics benchmark run by PC Magazine.

If Zortech C++ and dmc++ are fast, why is dmd's asm slow? I 
thought they used the same machine code backend.