To help LDC/GDC

[Johannes Pfau]

Am Mon, 8 Apr 2013 16:40:34 +0100
schrieb Iain Buclaw <ibuclaw at ubuntu.com>:

> On 8 April 2013 13:37, Manu <turkeyman at gmail.com> wrote:
> 
> > Oh my god... ..... this is the most upsetting thing I've heard all
> > day! :( No really, I have been SOOOO excited for so long about this
> > optimisation potential in D!
> > There's gotta be something that can be done! >_<
> >
> > Does the front end know if the function actually DOES assign to any
> > state? The compiler could easily work that out, and in the event it
> > doesn't actually perform any such assignment, it could be marked
> > pure for reals...
> >
> >
> Haven't looked, but it appears to have a general idea of this.  D
> 'weak pure' and 'const pure' may update an internal state (had the
> latter bite me hard once).  The only case where 'strong pure' might
> do this is by throwing an exception or an assert being thrown - this
> changes program state so can't be marked pure.
> 
> So having identified this, we can safely say that functions could
> only be 'C pure' in the following case:
> - Compiled function is 'strong pure'
> - Compiled function is 'nothrow'
> - We are compiling in release mode.
> 
> Only then we (the frontend) can safely say that 'this function has
> *absolutely* no side effects, so can be marked as pure'.   Pure is
> never inferred.
> 

Can't a strong pure + nothrow + release mode function still throw
errors? Or is this the "we don't guarantee anything regarding Errors"
case and we just don't care?