[Bug tree-optimization/36347] New: points-to sets should be always kept for call-clobbering

[rguenth at gcc dot gnu dot org]

typedef unsigned long my_uintptr_t;

int check_a(my_uintptr_t tagged_ptr);

int __attribute__((noinline)) try_a(my_uintptr_t x)
{
  my_uintptr_t heap[2];
  my_uintptr_t *hp = heap;

  hp[0] = x;
  hp[1] = 0;
  return check_a((my_uintptr_t)(void*)((char*)hp + 1));
}


<bb 2>:
  # heap_10 = VDEF <heap_9(D)>
  heap[0] = x_2(D);
  # heap_11 = VDEF <heap_10>
  heap[1] = 0;
  D.1562_4 = &heap + 1;
  D.1563_5 = (long unsigned int) D.1562_4;
  # heap_12 = VDEF <heap_11>
  D.1561_6 = check_a (D.1563_5);
  return D.1561_6;


The points-to solution for D.1562_4 is D.1562_4 = { heap }, but we drop
that to

D.1562_4, its value escapes, points-to anything

because the pointer is never dereferenced.  This causes all addressable
variables to escape at the call to check_a, which pessimizes code and
causes useless VOPs.


-- 
           Summary: points-to sets should be always kept for call-clobbering
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Keywords: missed-optimization, alias
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36347