[LLVMdev] Dependence Analysis [was: Flow-Sensitive AA]

[David Greene]

On Friday 22 August 2008 17:05, Vikram S. Adve wrote:
> On Aug 22, 2008, at 4:49 PM, John Regehr wrote:
> > Has anyone quantified the optimizations afforded by undefined signed
> > overflow?  I'd expect that the benefits are minimal for most codes.
>
> In most cases, I agree.  But for codes that depend heavily on
> dependence analysis, I would think that being conservative with index
> expressions would really kill any disambiguation capability and make
> many loop optimizations and other dependence-based optimizations much
> weaker.  For example, static scheduling of array intensive loops seems
> vulnerable to this.

Yes, exactly right.  Once you have wrapping arithmetic, the amount of
stuff you can know about an iteration space plummets.

                                                     -Dave