[LLVMdev] Checked arithmetic

[Jonathan S. Shapiro]

On Wed, 2008-03-26 at 11:02 -0700, Chris Lattner wrote:
> On Wed, 26 Mar 2008, Jonathan S. Shapiro wrote:
> > I want to background process this for a bit, but it would be helpful to
> > discuss some approaches first.
> >
> > There would appear to be three approaches:
> >
> >  1. Introduce a CC register class into the IR. This seems to be a
> >     fairly major overhaul.
> >
> >  2. Introduce a set of scalar and fp computation quasi-instructions
> >     that accept the same arguments as their computational counterparts,
> >     but produce *only* the condition code. For example:
> 
> Why not define an "add with overflow" intrinsic that returns its value and 
> overflow bit as an i1?

Chris:

I understand several simple ways to implement add with carry. Your
suggestion is one of them. What I'm trying to understand is how to
handle the conditional code issue generally.


shap