[Bug middle-end/86912] Function pointer imposes an optimization barrier

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86912

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2020-01-24
                 CC|                            |msebor at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
I'll confirm this but I'm not sure if the problem is substantively different
than something as simple as the following C program where GCC doesn't fold the
array reference to zero.  Even declaring the array at file scope doesn't help. 
(I'm pretty sure there is a report of this optimization opportunity somewhere
in Bugzilla.)

$ cat u.c && gcc -O2 -S -Wall -fdump-tree-optimized=/dev/stdout u.c
int f (int i)
{
  const int a[] = { 0, 0, 0 };
  return a[i];   // should be folded to return 0;
}

;; Function f (f, funcdef_no=0, decl_uid=1930, cgraph_uid=1, symbol_order=0)

f (int i)
{
  const int a[3];
  int _6;

  <bb 2> [local count: 1073741824]:
  MEM <unsigned long> [(int *)&a] = 0;
  a[2] = 0;
  _6 = a[i_5(D)];
  a ={v} {CLOBBER};
  return _6;

}