[Bug tree-optimization/94963] New: [11 Regression] Spurious uninitialized warning for static variable building glibc

[jsm28 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94963

            Bug ID: 94963
           Summary: [11 Regression] Spurious uninitialized warning for
                    static variable building glibc
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jsm28 at gcc dot gnu.org
  Target Milestone: ---

r11-39-gf9e1ea10e657af9fb02fafecf1a600740fd34409 ("tree-optimization/39612 -
avoid issueing loads in SM when possible") introduces a spurious warning
building the following code (reduced from glibc) with -O2 -Wall (for
aarch64-linux-gnu at least, probably for other targets.  The warning is
obviously bogus because it relates to a field of a static variable, which is
always initialized.

uninit.c: In function 'f':
uninit.c:30:6: warning: 'var_field_lsm.8' may be used uninitialized in this
function [-Wmaybe-uninitialized]
   30 |   if (var.field != 0)
      |      ^


Reduced testcase:

typedef struct
{
  int p1;
  int p2;
  int p3;
} P;
struct S
{
  int field;
};
extern int v2;
extern void foo (struct S *map);
static struct S var;
const P *pv;
int ps;
void
f (void)
{
  if (pv != 0)
    for (const P *ph = pv; ph < &pv[ps]; ++ph)
      switch (ph->p1)
        {
        case 1:
          v2 = ph->p2;
          break;
        case 2:
          var.field = ph->p3;
          break;
        }
  if (var.field != 0)
    foo (&var);
}