[Bug tree-optimization/50346] Function call foils VRP/jump-threading of redundant predicate on struct member

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50346

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c++                         |tree-optimization

--- Comment #3 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-10-12 10:10:15 UTC ---
Well, it's a tree optimization issue.  It's simple - the local aggregate f
escapes the function via the member function call to baz:

<bb 5>:
  foo::baz (&f);

and as our points-to analysis is not flow-sensitive for memory/calls this
causes f to be clobbered by the call to bar:

<bb 2>:
  f.b = 0;
  # USE = nonlocal null { f }
  # CLB = nonlocal null { f }
  retval.0_2 = bar ();

as neither the bodies of baz nor bar are visible there is nothing we can do
here (short of re-doing points-to analysis flow-sensitive for memory).

f.b is partially redundant, so you see later jump-threading at work optimizing
the path following the f.b = true assignment.