Using an external Assembler with D

[solidstate1991]

In order to make one of my own code more readable (and hopefully 
to avoid a lot of compiling errors under LDC, which don't happen 
in DMD for some reason), I'm planning to put my assembly 
functions into separate files for each system that needs them, 
mainly due to the lack of proper SIMD support, mainly due to 
these functions are relatively easy to implement. Here's a few 
questions of mine:

- Can I return vectors in XMM registers and accept arguments as 
vectors in them?
- How much is the D ABI differs on DMD and LDC for x86? I'm 
planning to support both (with mainly using DMD as a debug 
compiler for its speed), and want the most universal solution 
possible.