== operator

[anonymous via Digitalmars-d]

On Sunday, 4 January 2015 at 04:43:17 UTC, Jonathan Marler wrote:
> The problem I see is that in almost all cases the 
> opEquals(Object) method will have to perform a cast back to the 
> original type at runtime.  The problem is this isn't doing any 
> useful work.  The current '==' operator passes the class as an 
> Object to a generic opEquals method which eventually gets 
> passed to a method that must cast it back to the original type.
>  Why not just have the == operator rewrite the code to call a 
> "typed" opEquals method?  Then no casting is necessary.
[...]
> run 1 (loopcount 10000000)
>   x.x == y.x               : 6629 microseconds
>   x.opEquals(y)            : 6680 microseconds
>   x.opEquals(cast(Object)y): 89290 microseconds
>   x == y                   : 138572 microseconds
> run 2 (loopcount 10000000)
>   x.x == y.x               : 6124 microseconds
>   x.opEquals(y)            : 6263 microseconds
>   x.opEquals(cast(Object)y): 90918 microseconds
>   x == y                   : 132807 microseconds

I made made opEquals(Object) final and tried with ldc. Gives me 
these times:

run 1 (loopcount 10000000)
   x.x == y.x               : 0 microseconds
   x.opEquals(y)            : 0 microseconds
   x.opEquals(cast(Object)y): 0 microseconds
   x == y                   : 108927 microseconds
run 2 (loopcount 10000000)
   x.x == y.x               : 0 microseconds
   x.opEquals(y)            : 0 microseconds
   x.opEquals(cast(Object)y): 0 microseconds
   x == y                   : 106700 microseconds

Threw some `asm {}`s in there to make it less hyper-optimized:

run 1 (loopcount 10000000)
   x.x == y.x               : 4996 microseconds
   x.opEquals(y)            : 3932 microseconds
   x.opEquals(cast(Object)y): 3924 microseconds
   x == y                   : 109300 microseconds
run 2 (loopcount 10000000)
   x.x == y.x               : 3068 microseconds
   x.opEquals(y)            : 2931 microseconds
   x.opEquals(cast(Object)y): 2963 microseconds
   x == y                   : 108093 microseconds

I think (final) opEquals(Object) itself is ok.

A final opEquals(Object) is faster with dmd, too. But it's 
nowhere near the others. So apparently dmd misses some 
optimization there, presumably inlining.