exceptions and optimization

[Peter Jacobs]

Toward the end of Walter's recent talk, D at 20, he says 
something to the effect that optimizations are disabled when 
exceptions can be thrown.  We have a compressible flow solver in 
which it is very convenient to be able to throw an exception from 
deep within the code and catch it at a relatively high level 
where we can partially recover and continue the calculation.  
Because our calculations can run for days across hundreds of 
processors, we also care about letting the optimizer do its best. 
In what parts of our program would the optimizer be disabled 
because of the presence of the exception and its handling code?  
How do we tell?