Performance improvements for D / DMD compiler.

[BCS]

Dave wrote:
> 
> What's on your wish-list (let's leave the GC and other library 
> functionality out of this for now <g>)?
> 
> Here's mine:
>   - Better floating point code generation
>   - Put the tail-recursion optimization back in
>   - Omit frame pointers w/ -O switch
>   - Improved in-lining (don't arbitrarily exclude functions w/ inout 
> parameters and loops).
>   - Auto-finalization.

Better const folding/handling, local const values are put into the stack 
frame even if they are never used. (disassemble a run of my bignum 
template to see this).

preferential inlining of functions with lazy arguments or that take the 
form:

fn(delegate() dg)
{
	//short code
	dg();
	//short code
}

aggressive de-virtualization of method calls.