Re: [RFC] Isolate & simplify paths with undefined behaviour

[Marc Glisse <marc dot glisse at inria dot fr>]

On Fri, 18 Oct 2013, Jeff Law wrote:

> On 10/18/13 12:47, Marc Glisse wrote:
> > * tree-vrp has a function infer_nonnull_range, do you think we could
> > share it? We now store the VRP ranges for integers, but not for
> > pointers. If we did (or maybe just a non-null bit), the pass could just
> > test that bit on the variable found in the PHI.
> I'm not sure what can really be shared here -- this patch searches for PHIs 
> where one or more of the args is a NULL pointer.  The NULL pointer will be 
> explicit in the PHI arg.

But once you have that pointer defined by a PHI containing a zero, you 
look at all its uses, trying to find one that proves the pointer is 
non-zero (only dereferences for now, but you have a comment about the 
non-null attribute). And infer_nonnull_range precisely says whether a 
statement proves that a pointer is non-zero (well, there may be a few 
subtle differences, and some tests might need to move between 
infer_value_range and infer_nonnull_range). I am just talking of replacing 
20 lines of code with a function call, not a huge sharing I agree...

Storing the VRP info might not actually help, since you need to know 
starting from which statement the pointer is non-zero.

--
Marc Glisse