[Bug c++/83058] [6/7/8 Regression] ICE on C++ code with negative array index: in warn_placement_new_too_small, at cp/init.c:2666

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83058

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |msebor at gcc dot gnu.org
   Target Milestone|8.0                         |6.5
            Summary|[8 Regression] ICE on C++   |[6/7/8 Regression] ICE on
                   |code with negative array    |C++ code with negative
                   |index: in                   |array index: in
                   |warn_placement_new_too_smal |warn_placement_new_too_smal
                   |l, at cp/init.c:2666        |l, at cp/init.c:2666

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Not so recent regression, started with r229827.
There are multiple bugs in that code:
if (CONSTANT_CLASS_P (adj))
should really be a test for TREE_CODE (adj) == INTEGER_CST, tree_to_shwi is
going to ICE on anything else.
      const_tree adj = TREE_OPERAND (oper, 1);
      if (!use_obj_size && CONSTANT_CLASS_P (adj))
        adjust += tree_to_shwi (adj);
similarly, plus there is no checking of addition overflows.
I think it might be better to turn adjust into an offset_int in which you
compute everything and then check if it can actually be used (or force
use_obj_size otherwise).
      gcc_checking_assert (0 <= adjust);
this is where we ICE.  The comparison operand order is incorrect too.
      if (CONSTANT_CLASS_P (size))
Again, wrong check.  Should be probably if (tree_fits_uhwi_p (size)).
        bytes_need = tree_to_uhwi (size);
      else if (nelts && CONSTANT_CLASS_P (nelts))
          bytes_need = tree_to_uhwi (nelts)
            * tree_to_uhwi (TYPE_SIZE_UNIT (type));

The above is also misformatted, should be
        bytes_need = tree_to_uhwi (nelts)
                     * tree_to_uhwi (TYPE_SIZE_UNIT (type));
or
        bytes_need = (tree_to_uhwi (nelts)
                      * tree_to_uhwi (TYPE_SIZE_UNIT (type)));
or
        bytes_need
          = tree_to_uhwi (nelts) * tree_to_uhwi (TYPE_SIZE_UNIT (type)));
What about the case when TYPE_SIZE_UNIT doesn't fit into uhwi?  That will ICE
too.

      else if (tree_fits_uhwi_p (TYPE_SIZE_UNIT (type)))
        bytes_need = tree_to_uhwi (TYPE_SIZE_UNIT (type));