dmd codegen improvements

[Temtaime via Digitalmars-d]

So comparing to llvm the idea of optimizing backend comes with:

1) LLVM optimizes code much better than DMD for now. And it's in 
active development, so it always will be far from DMD.
2) LLVM has over 120k commits, it has many financial investments 
from Google and Apple. Are you sure that ONE Walter can achieve 
what they done ?
3) LLVM supports many platforms while DMD will never support 
anything different from x86.
4) LLVM has free licensing, while DMD's backend is not.
5) Changing the backend often causes weird regressions to appear, 
it causes users to be afraid.

I think it's really better to fix current bugs than waste the 
time.