[LLVMdev] RFC: New Exception Handling Proposal

[Bill Wendling]

On Nov 18, 2009, at 2:22 PM, Bill Wendling wrote:

> Throw: A New Instruction
> ------------------------
>
> The `unwind' instruction has no semantic meaning outside of an  
> exception
> context. I propose removing it as an instruction, and replacing it
> with a new,
> more descriptively named instruction called `throw'. The `throw'
> instruction
> would take the exception object as its only parameter. Its semantic
> would be to
> throw that exception object. Essentially, rethrowing that exception.
>
> Syntax:
>
>         throw i8* %eh_ptr
>
>
Addendum: It was pointed out to me in a private email that this new  
"throw" instruction may not be useful. If you have two functions being  
merged into the same module, but both with different instructions to  
do the actual "throw", then this instruction as described here won't  
work. There's the possibility of adding a function parameter to this,  
but that obviates this new instruction (why not emit a direct call  
instead?). The function may be added to the function type, similar to  
the personality function. But that's even more baggage on the function  
type.

There would only be a marginal conceptual win, which isn't enough to  
warrant a new instruction.

-bw