Compiler could elide many more postblit constructor calls

[Diggory]

On Sunday, 30 June 2013 at 10:21:12 UTC, TommiT wrote:
> Perhaps an interesting observation about this is that while in 
> C++ const correctness literally never improves performance [1], 
> in D (if these optimizations were implemented) const 
> correctness could potentially increase performance considerably 
> (if there are expensive postblits). Thus, functions should take 
> arguments by const value rather than value, when the type of 
> the parameter is either templated or has postblit.
>
> [1] Except with constant folding or when the compiler can put 
> const data to rommable memory and then share it with multiple 
> instances of the same program.

Precisely, although something that could improve performance even 
more would be escape analysis. In this example, if the compiler 
can prove that there are no global/parameter mutable references 
to a given variable then it will be able to apply the 
optimisation regardless of purity.