waccess: Remove visited bitmap and stop on EDGE_ABNORMAL

waccess: Remove visited bitmap and stop on EDGE_ABNORMAL

On Fri, Mar 04, 2022 at 02:58:37PM +0100, Jakub Jelinek via Gcc-patches wrote:
> On Thu, Mar 03, 2022 at 05:08:30PM -0700, Martin Sebor wrote:
> > > 1) shouldn't it give up for EDGE_ABNORMAL too?  I mean, e.g.
> > >     following a non-local goto forced edge from a noreturn call
> > >     to a non-local label (if there is just one) doesn't seem
> > >     right to me
> >
> > Possibly yes.  I can add it but I don't have a lot of experience with
> > these bits so if you can suggest a test case to exercise this that
> > would be helpful.
>
> Something like:
> void
> foo (void)
> {
>   __label__ l;
>   __attribute__((noreturn)) void bar (int x) { if (x) goto l; __builtin_trap (); }
>   bar (0);
> l:;
> }
> shows a single EDGE_ABNORMAL from the bar call.
> But it would need tweaking for the ptr use and clobber.
>
> > > 2) if EDGE_DFS_BACK is computed and 1) is done, is there any
> > >     reason why you need 2 levels of protection, i.e. the EDGE_DFS_BACK
> > >     check as well as the visited bitmap (and having them use
> > >     very different answers, if EDGE_DFS_BACK is seen, the function
> > >     will return false, if visited bitmap has a bb, it will return true)?
> > >     Can't the visited bitmap go away?
> >
> > Possibly.  As I said above, I don't have enough experience with these
> > bits to make (and test) the changes quickly, or enough bandwidth to
> > come up to speed on them.  Please feel free to make these improvements.
>
> I'll change that if it passes testing.

Here is a patch to do both.  I don't think we really need to have a testcase
for the EDGE_ABNORMAL case (Martin, feel free to add it later), abnormal
edges simply aren't normal control flow and what exactly it means varies.

2022-03-05  Jakub Jelinek  <jakub@redhat.com>

	* gimple-ssa-warn-access.cc (pass_waccess::use_after_inval_p): Remove
	visited bitmap and its use.  Also punt on EDGE_ABNORMAL edges.