[LLVMdev] difference between alias set tracker and alias analysis evaluator

[Chris Lattner]

On May 29, 2009, at 3:35 AM, Amr Yehia wrote:

>
> so my questions finally are:
> - why is there is a difference between the 2 results,
> - how can i get the alias set tracker to give me all the aliasing
> results returned by alias analysis evaluator
>

This is an inherent limitation of aliassettracker: it unions the  
results of alias queries into "sets".  Because of this, transitive  
results cannot be distinguished.  For example, if "A mayalias B", and  
"B mayalias C" alias set tracker will tell you that "a and c are in  
the same set" even if AliasAnalysis knows they don't alias.  You can  
use AliasAnalysis directly or use MemoryDependenceAnalysis for more  
precise results.

-Chris