C++ return value versus exception performance

Question

Somewhere I have read that modern Intel processors have low-level hardware for implementing exceptions and most compilers take advantage of it, to the effect that exceptions become faster than returning results state using variables.

Is it true? are exceptions faster than variables as far as returning state/responding to state? reading stack overflow on the topic seems to contradict that.

Thank you

Answer 1

Be aware that there's ambiguity in the term "exception handler." I believe you'll find that hardware folks when talking about exceptions mean things like:

1. Hardware interrupts, aka signals, whose handlers are sometimes called exception handlers (see http://pages.cs.wisc.edu/~smoler/x86text/lect.notes/interrupts.html)
2. Machine check exceptions, which halt the computer if something in hardware goes wrong (see http://en.wikipedia.org/wiki/Machine_Check_Exception)

Neither of those has anything to do with C++'s exception handling facility.

As a counterexample, I have at least one anecdotal data point where exceptions were way slower than return codes: that was on Intel hardware alright, but with gcc 2.95 and a very large set of code with a very large exception table, that was constructed the first time an exception was thrown. Subsequent exceptions were fast, but by then the damage was usually done. Admittedly, gcc 2.95 is pretty ancient, but it should be enough to caution you about making generalizations about the speed of C++ exception handling, even on Intel hardware.