Re: short-circuit control forms

[Dale Stanbrough <dale@cs.rmit.edu.au>]

Ted Dennison wrote:

>  I'm not sure what the LRM's silence on a subject means in this case. But
> assuming it means "all bets are off", then it looks to me like compilers 
> are
> perfectly free to short-circuit, or even reorder and short-circuit normal
> conditional expressions.


The LRM guarentees order of execution for short circuit form, which is
from left to right.

Not all short circuit forms need be faster, this can depend on the 
architecture that is being compiled for. For example the following
code

   if x = 2 and y = 3 then

could have both comparisons scheduled on a modern processor with 
numerous integer units so that they occur simultaneously.

As always, measure before you optimise.

Dale