Re: [Cardinal-dev] Compiler structure / AST format

[Einar Karttunen]

On 25.04 11:53, Dan Sugalski wrote:
> At 4:05 AM +0300 4/25/02, Einar Karttunen wrote:
> >The reason for the immediate is the optimiser pass and the 
> >complexity of backends.
> >* backends need to only know about the intermediate code not the AST
> >* frontends and backends can be switched with no recoding
> >* some optimisations common to all backends are very unnatural at 
> >the AST level
> 
> I'll point out that some optimisations common to all backends are 
> very natural to do at the AST level. Most compilers I know of have at 
> least three different intermediate representations of the code for 
> the optimiser because of the different characteristics of the 
> different optimisations. Some work best with a high-level 
> representation, some with a medium-level representation, and some 
> with a low-level representation.

Of course some optimisation is best done in AST level, and I think
my message made it clear. Most compilers I know about have just
two level if you don't count instruction scheduling as a third
level.

- Einar Karttunen