AST files instead of DI interface files for faster compilation and easier distribution

[Jonathan M Davis]

On Thursday, June 14, 2012 10:03:05 Don Clugston wrote:
> On 13/06/12 16:29, Walter Bright wrote:
> > On 6/13/2012 1:07 AM, Don Clugston wrote:
> >> On 12/06/12 18:46, Walter Bright wrote:
> >>> On 6/12/2012 2:07 AM, timotheecour wrote:
> >>>> There's a current pull request to improve di file generation
> >>>> (https://github.com/D-Programming-Language/dmd/pull/945); I'd like to
> >>>> suggest
> >>>> further ideas.
> >>>> As far as I understand, di interface files try to achieve these
> >>>> conflicting goals:
> >>>> 
> >>>> 1) speed up compilation by avoiding having to reparse large files over
> >>>> and over.
> >>>> 2) hide implementation details for proprietary reasons
> >>>> 3) still maintain source code in some form to allow inlining and CTFE
> >>>> 4) be human readable
> >>> 
> >>> (4) was not a goal.
> >>> 
> >>> A .di file could very well be a binary file, but making it look like D
> >>> source enabled them to be loaded with no additional implementation work
> >>> in the compiler.
> >> 
> >> I don't understand (1) actually.
> >> 
> >> For two reasons:
> >> (a) Is lexing + parsing really a significant part of the compilation
> >> time? Has
> >> anyone done some solid profiling?
> > 
> > It is for debug builds.
> 
> Iain's data indicates that it's only a few % of the time taken on
> semantic1().
> Do you have data that shows otherwise?
> 
> It seems to me, that slow parsing is a C++ problem which D already solved.

If this is the case, is there any value at all to using .di files in druntime 
or Phobos other than in cases where we're specifically trying to hide 
implementation (e.g. with the GC)? Or do we still end up paying the semantic 
cost for importing the .d files such that using .di files would still help with 
compilation times?

- Jonathan M Davis