Re: calling convention optimisation & const/immutable ref

[Johan Engelen via Digitalmars-d]

On Monday, 7 November 2016 at 16:48:55 UTC, John Colvin wrote:
Some people use ref for performance to prevent the copying that 
must occur when passing by value.

This reminds me of an LLVM presentation by Chandler, mentioning 
that passing by reference may hamper the optimization of code 
(because memory becomes involved). I don't think he gave a clear 
example, but one thing I can think of is potential aliasing:
void foo(ref LargeThing a, ref LargeThing b), where a and b may 
alias partly.
To do the "ref" optimization for _all_ large function parameters 
per default sounds like a bad idea.

Also, how would I turn the optimization off (I guess extern(C++) 
would do that?)? What if my function needs a local copy (say, in 
multithreaded stuff), and I want that copy to be const?

-Johan