[LLVMdev] aborting on invalid code

Chris Lattner clattner at apple.com
Mon Oct 13 11:07:29 PDT 2008

On Oct 13, 2008, at 10:56 AM, Vikram S. Adve wrote:
> Andrew and I (and another faculty member here) are working on software
> recovery techniques for run-time errors that would otherwise be fatal,
> so I am curious about this answer.  Why do you think these cases
> should not be fixed with exceptions?  What if a client wants to
> *recover* in some manner, e.g., by emulating missing instructions or
> transforming the code (or any of a variety of other recovery
> strategies), but not just report a failure to the external world?

Exceptions have a high cost in terms of code size, binary size, and  
even a bit of execution time.  Also, they don't magically make the  
code safe from any error: code has to be designed specifically to use  
RAII and other techniques to handle exceptions properly.  Reading a C+ 
+ trade magazines/books about EH topics will give you an idea of the  
complexity involved in doing it right.  Further, as I mentioned up- 
thread, turning aborts into exception throws won't save you from null  
pointer or garbage pointer dereferences.

As I said before, LLVM libraries have to serve multiple clients.  Code  
size is a very important aspect of this.  I'd love to build with -fno- 
rtti to get another 5% back.


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