[Bug tree-optimization/89697] New: SRA prevents -Wuninitialized warning

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89697

            Bug ID: 89697
           Summary: SRA prevents -Wuninitialized warning
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

For

struct my_struct {
    int i1;
    int i2;
};
static struct my_struct s1;

void
wtest(void)
{
  struct my_struct s2; /* not initialized */

  if (s1.i1 == 0) {
      s1 = s2; /* assigning uninitialized variable */
  }
}

without SRA, thus -O0 or -On with -fno-tree-sra reports:

t.c: In function ‘wtest’:
t.c:13:10: warning: ‘s2’ may be used uninitialized in this function
[-Wmaybe-uninitialized]
   13 |       s1 = s2; /* assigning uninitialized variable */
      |       ~~~^~~~

but when SRA is enabled we get no warning.  This is even though the
uninitialized use is clearly visible in the IL:

wtest ()
{
  int s2$i2;
  int s2$i1;
  int _1;

  <bb 2> [local count: 1073741824]:
  _1 = s1.i1;
  if (_1 == 0)
    goto <bb 3>; [50.00%]
  else
    goto <bb 5>; [50.00%]

  <bb 5> [local count: 536870912]:
  goto <bb 4>; [100.00%]

  <bb 3> [local count: 536870913]:
  MEM[(struct my_struct *)&s1] = s2$i1_4(D);
  MEM[(struct my_struct *)&s1 + 4B] = s2$i2_6(D);

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

}