More pure optimizations

[Brad Roberts]

Brad Roberts wrote:
> On a related note, I started this past weekend playing with automatic 
> detection / proof of pureness in the d2 codebase.  It's a long way from 
> complete, but could allow the optimizer to find pure by implementation 
> rather than pure by definition cases to play with.  The same code can be 
> used to validate the pure attribute and warn or error on violations.
> 
> Once I get it a semi-useful state, I'll toss a patch into a bug report so 
> others can see it.  Right now it's too embrionic to share. :(
> 
> Later,
> Brad

As I feared.. within an hour of posting this I realized a fatal flaw in my
design.  I've some ideas for how to do what I want, but I need to think more.

Sigh,
Brad