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digitalmars.D - DMD: Finding symbol value references to enable more move optimizations

I'm currently trying to understand if it's possible to add more 
move-optimizations in parameter passing for those parameters 
whole symbols aren't used after the call or for `const` or 
`immutable` parameters to ` safe pure` (strictly pure) functions. 
This similar to function call optimizations possible in Rust but 
less restrictive because the symbol is allowed to be used after 
the call aswell.

Could somebody please highlight suitable places in DMD that 
checks if the value of a specific symbol is read or written to, 
typically inside a given `Scope` instance?

My guess is `doCopyOrMove` in `expression.d` is good contender, 

Is this the place where I should scan for further references to 
expression if it's an Lvalue?

If there currently is no such code that does this, does anybody 
have any advice on how to write this?

Further, AFAICT, parameters passed as `const` or `immutable` to 
` safe pure` functions can also be passed with a move.

This traversal is a key-feature that could also provide better 
diagnostics for unused symbols.

I also realize the risk of introducing quadratic complexity in 
`doCopyOrMove` but this can be avoided by memoizing the result of 
the symbol scan upon the first call to `doCopyOrMove` for the 
Lvalue case.

I've tried posting this the DMD group but it enters an infinite 
post loop. I have registered my email and name on the mailing 
list aswell.
Sep 27 2016