[PATCH] D20776: [CFLAA] Teach cfl-aa to understand heap memory allocation

[Jia Chen via llvm-commits]

On Wed, Jun 1, 2016 at 12:38 PM, Daniel Berlin <dberlin at dberlin.org> wrote:
> Sure, and FWIW, it depends on the definition of unused.
> GCC's andersen's analysis eliminates variables (ie prior to solving) that
> are not treated like pointers.
> That is, if they are not dereferenced, etc, it simply ignores them.  You can
> prove this is correct, and is common (see
> https://www.lib.utexas.edu/etd/d/2009/hardekopfb48332/hardekopfb48332.pdf
> and http://aria.cs.vt.edu/refs/docs/pldi00.ps for non-pointer elimination)

I agree that it is possible. However, the current cfl-aa
implementation is not doing something that gcc does (it is even less
precise than Andersen's analysis at this point!). It just looks at
instructions, translates them to edges, and add edges to
StratifiedSets. What bothers me here is why we must explicitly add
assign edges for things like unused allocas, e.g. malloc() return
values, and free() argument. In other words, the suspicion is on the
implementation, not the underlying approach.