[Bug ipa/65502] New: pure-const should play well with clobbers.

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65502

            Bug ID: 65502
           Summary: pure-const should play well with clobbers.
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ipa
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hubicka at gcc dot gnu.org

I just noticed that C++ destructors are not conisdered const/pure:

 local analysis of Smarts::IterateScheduler<Smarts::Stub>::~IterateScheduler()
   scanning: MEM[(struct  &)this_2(D)] ={v} {CLOBBER};
    Indirect ref write is not const/pure
  scanning: return;
Smarts::IterateScheduler<Smarts::Stub>::~IterateScheduler() (struct
IterateScheduler * const this)
{
  <bb 2>:
  MEM[(struct  &)this_2(D)] ={v} {CLOBBER};
  return;

}

This is of course wrong, empty function is const.  One issue however is that we
want to preserve CLOBBER when inlining, so during early passes we may want to
keep clobbers nonpure.