size_t for length on x64 will make app slower than on x86?

[FrankLike via Digitalmars-d]

> Don't profile with out optimzation.
> Add "-O -inline -release -boundscheck=off" to your dmd 
> arguments.

I mean projects moved from x86 to x64, 'cast(int)length ' is 
better than 'size_t i=(something).length '.