[Bug tree-optimization/106155] New: [12/13 Regression] spurious "may be used uninitialized" warning

[vincent-gcc at vinc17 dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106155

            Bug ID: 106155
           Summary: [12/13 Regression] spurious "may be used
                    uninitialized" warning
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vincent-gcc at vinc17 dot net
  Target Milestone: ---

With "-O -Wmaybe-uninitialized", I get a spurious "may be used uninitialized"
on the following code on an x86_64 Debian/unstable machine:

int *e;
int f1 (void);
void f2 (int);
long f3 (void *, long, int *);
void f4 (void *);
int *fh;

void tst (void)
{
  int status;
  unsigned char badData[3][3] = { { 7 }, { 16 }, { 23 } };
  int badDataSize[3] = { 1, 1, 1 };
  int i;

  for (i = 0; i < 3; i++)
    {
      int emax;
      if (i == 2)
        emax = f1 ();
      status = f3 (&badData[i][0], badDataSize[i], fh);
      if (status)
        {
          f1 ();
          f1 ();
          f1 ();
        }
      f4 (fh);
      *e = 0;
      f1 ();
      if (i == 2)
        f2 (emax);
    }
}

Note that even a small change such as changing "long" to "int" as the second
parameter of f3 makes the warning disappear.

$ gcc-12 -O -Wmaybe-uninitialized -c -o tfpif.o tfpif.c
tfpif.c: In function ‘tst’:
tfpif.c:31:9: warning: ‘emax’ may be used uninitialized [-Wmaybe-uninitialized]
   31 |         f2 (emax);
      |         ^~~~~~~~~
tfpif.c:17:11: note: ‘emax’ was declared here
   17 |       int emax;
      |           ^~~~
$ gcc-12 --version
gcc-12 (Debian 12.1.0-5) 12.1.0
[...]

$ gcc-snapshot -O -Wmaybe-uninitialized -c -o tfpif.o tfpif.c
tfpif.c: In function 'tst':
tfpif.c:31:9: warning: 'emax' may be used uninitialized [-Wmaybe-uninitialized]
   31 |         f2 (emax);
      |         ^~~~~~~~~
tfpif.c:17:11: note: 'emax' was declared here
   17 |       int emax;
      |           ^~~~
$ gcc-snapshot --version
gcc (Debian 20220630-1) 13.0.0 20220630 (experimental) [master
r13-1359-gaa1ae74711b]
[...]

No such issue with:
  gcc-9 (Debian 9.5.0-1) 9.5.0
  gcc-10 (Debian 10.4.0-1) 10.4.0
  gcc-11 (Debian 11.3.0-4) 11.3.0

I detected this issue by testing GNU MPFR. The above code is derived from
"tests/tfpif.c", function check_bad.