[Bug tree-optimization/104356] [12 Regression] divide by zero trap is being removed now when it should not be in some cases

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104356

--- Comment #14 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
> OK, so a division by zero is not invoking undefined behavior but is
> well-defined and traps.  And the idea is that -fnon-call-exceptions alone
> carries this over to middle-end semantics?  (I don't think it does that at
> the moment, with or without the rev. in question)

Why?  It's exactly like any other trapping operation, see the numerous
predicates in tree-eh.cc, most notably operation_could_trap_helper_p:

  switch (op)
    {
    case TRUNC_DIV_EXPR:
    case CEIL_DIV_EXPR:
    case FLOOR_DIV_EXPR:
    case ROUND_DIV_EXPR:
    case EXACT_DIV_EXPR:
    case CEIL_MOD_EXPR:
    case FLOOR_MOD_EXPR:
    case ROUND_MOD_EXPR:
    case TRUNC_MOD_EXPR:
      if (!TREE_CONSTANT (divisor) || integer_zerop (divisor))
        return true;