Which optimisations are are easier or perhaps only possible in the frontend ?

[John Colvin via Digitalmars-d]

On Wednesday, 10 December 2014 at 11:07:34 UTC, Stefan Koch wrote:
> Hello guys,
> I want to work on optimisations in the semantic analysis stage.
>
> Could you chime in with thoughts about what can only be there 
> and not in llvm-ir for example ?
>
> Thanks Stefan

Well it really depends how descriptive your IR happens to be.

Perhaps high-level promises about code that the compiler can't 
see. E.g. something like
@commutative float[] convolve(float[] a, float[] b);