[Bug middle-end/102700] New: [Diagnostics] uninitialized warning missing after O2 vectorization.

[crazylht at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102700

            Bug ID: 102700
           Summary: [Diagnostics] uninitialized warning missing after O2
                    vectorization.
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: crazylht at gmail dot com
  Target Milestone: ---
              Host: x86_64-pc-linux-gnu

testcase is from g++.dg/warn/Wuninitialized-13.C
struct shared_count {
  shared_count () { }
  shared_count (shared_count &r)
    : pi (r.pi) { }     // { dg-warning "\\\[-Wuninitialized" "" { xfail {
i?86-*-* x86_64-*-* } } }
  int pi;
};

// There's another (redundant) -Wuninitialized on the line below.
struct shared_ptr {
  int ptr;
  shared_count refcount;
};

struct Bar {
  Bar (int, shared_ptr);
};

void g () {
  shared_ptr foo;
  Bar (0, foo);
}

After vectorization
.C.211.uninit1

;; Function g (_Z1gv, funcdef_no=6, decl_uid=4497, cgraph_uid=13,
symbol_order=12)

void g ()
{
  int * vectp.11;
  vector(2) int * vectp.10;
  vector(2) int vect__6.9;
  int * vectp.8;
  vector(2) int * vectp_foo.7;
  struct shared_ptr foo;
  struct shared_ptr D.4566;
  struct Bar D.4567;

  <bb 2> [local count: 1073741824]:
  [test2.C:6:19] MEM[(struct shared_count *)[test2.C:23:14] &foo + 4B] ={v}
{CLOBBER};
  [test2.C:13:8] vect__6.9_12 = MEM <vector(2) int> [(int *)&foo]; 
  [test2.C:8:5] MEM[(struct shared_count *)[test2.C:24:3] &D.4566 + 4B] ={v}
{CLOBBER};
  [test2.C:13:8] MEM <vector(2) int> [(int *)&D.4566] = vect__6.9_12;
  [test2.C:24:3] Bar::Bar ([test2.C:24:3] &D.4567, 0, [test2.C:24:3] &D.4566);
  [test2.C:24:3] D.4567 ={v} {CLOBBER};
  [test2.C:24:3] D.4566 ={v} {CLOBBER};
  foo ={v} {CLOBBER};
  [test2.C:25:1] return;

}

MEM <vector(2) int> [(int *)&foo];  is used instead of _6 = foo.ptr; which is
missed by warn_uninitialized_vars?