optimizing calling conventions for function returns

[Paul Brook]

> Has work been done to evaluate a calling convention that takes error
> checks like this into account? Are there size/performance wins? Or am
> I just reinventing a variation on exception handling?

This introduces an extra stack push and will confuse a call-stack branch 
predictor. If both the call stack and the test are normally predicted 
correctly I'd guess this would be a performance loss on modern cpus.

Paul