On Monday, 8 April 2013 at 12:37:48 UTC, Manu wrote:
On 8 April 2013 21:46, Iain Buclaw <[email protected]> wrote:
Only builtins are pure in the sense of 'C'. Even functions
considered
PUREstrong by the frontend may update an internal state, so
the rules just
don't apply. Except for maybe global functions... In any
case, the only
benefit you can reap from 'D pure' functions are that they are
more likely
to be const-folded / inlined.
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...
Iain, are you sure about that? (No offense, but you have been
wrong about what GCC can/can't do in the past. :P) Could you
maybe elaborate a bit and present a counterexample? It might also
be a question of how the »as-if« rule is really defined for pure
function calls.
In any case, if the source is available, the LLVM optimizer is
usually very good at figuring out »pure for reals« (inferring the
LLVM 'readnone' attribute). Obviously, this doesn't help you when
you are doing separate compilation, though.
David
