[Bug c++/90947] [9/10 Regression] Simple lookup table of array of strings is miscompiled

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90947

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |ASSIGNED
           Keywords|                            |wrong-code
   Last reconfirmed|                            |2019-06-20
                 CC|                            |msebor at gcc dot gnu.org
         Resolution|DUPLICATE                   |---
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=89980
     Ever confirmed|0                           |1
            Summary|Simple lookup table of      |[9/10 Regression] Simple
                   |array of strings is         |lookup table of array of
                   |miscompiled                 |strings is miscompiled

--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
This is actually a different bug in the same commit.  A simpler test case is
this:

  void f (void)
  { 
    const char* a[2][2] = {
      { "0", "1" },
      { "", 0 }
   };

    if (!a[1][0])   // should be folded to false with -O
      __builtin_abort ();
  }

There is code in place to handle this kind of initialization:

      /* Pointers initialized to strings must be treated as non-zero
         even if the string is empty.  */
      tree init_type = TREE_TYPE (elt_init);
      if ((POINTER_TYPE_P (elt_type) != POINTER_TYPE_P (init_type))
          || !initializer_zerop (elt_init))
        last_nonzero = index;

This was added in r270177 to fix pr89980.  Unfortunately, the handling is
incomplete and the test insufficient to expose it.