[Bug tree-optimization/90122] New: inequality of addresses of distinct objects not folded

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90122

            Bug ID: 90122
           Summary: inequality of addresses of distinct objects not folded
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

In the test case below GCC folds the second test (as expected, on the
assumption that distinct declarations refer to distinct objects) but fails to
fold the first.

Clang folds both (into false and true, respectively).  GCC will only do that if
a and b are static or local.

Same with extern arrays of known size.

$ cat x.c && gcc -O2 -S -Wall -Wextra -fdump-tree-optimized=/dev/stdout
-fno-common x.c
extern int a, b;

void foo ();
void bar ();

void f (void)
{
  if (&a == &b)
    foo ();

  int i = a;
  b = 0;
  if (i != a)
    bar ();
}

;; Function f (f, funcdef_no=0, decl_uid=1910, cgraph_uid=1, symbol_order=2)

Removing basic block 5
f ()
{
  <bb 2> [local count: 1073741824]:
  if (&a == &b)
    goto <bb 3>; [17.43%]
  else
    goto <bb 4>; [82.57%]

  <bb 3> [local count: 187153200]:
  foo ();

  <bb 4> [local count: 1073741824]:
  b = 0;
  return;

}