[Bug middle-end/98583] New: missing -Wuninitialized reading from a second VLA in its own block

[msebor at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98583

            Bug ID: 98583
           Summary: missing -Wuninitialized reading from a second VLA in
                    its own block
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

GCC diagnoses the uninitialized accessed in h1() but if fails to detect the
same invalid access in h2().

$ cat x.c && gcc -O2 -S -Wall x.c
void f (int*);
void g (int);

void h1 (int n)
{
  int a[n];
  f (a);

  int b[n];
  g (b[1]);        // -Wuninitialized (good)
}

void h2 (int n, int i, int j)
{
  if (i)   // ditto without this if...
    {
      int a[n];
      f (a);
    }

  if (j)   // ...or this if...
    {
      int b[n];
      g (b[1]);    // missing warning
    }
}

x.c: In function ‘h1’:
x.c:10:3: warning: ‘*b[1]’ is used uninitialized [-Wuninitialized]
   10 |   g (b[1]);        // -Wuninitialized (good)
      |   ^~~~~~~~