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Re: data dependence for pointers broken?


> > 
> > Except that it doesn't seem to work for even the simplest of test
> > cases.  For instance, it reports dont_know for two uses of the
> > same SSA_NAME. 
> 
> 
> >  This doesn't fill me with confidence ...
> 
> We have code on autovec to do more advanced data dependence testing.
> 
> However, in general, data dependence testing on pointers is a losing
> proposition, because it involves a lot of aliasing work to determine
> whether you could have put one piece of memory in the way of the other,
> instead of just simple array dependence, where you know the aggregates
> are disjoint.

I.E. you have to start proving a lot of stuff about the base, and verify
the base doesn't change, etc.

This is why most compilers implement array form recovery, even in cases
where you are iterating through a pointer (recovering an indexing form),
so that you can do regular data dependence stuff on it.

This was my goal with the MEM_REF stuff.




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