[Bug c++/83273] if constexpr does not fail with run-time conditions

jakub at gcc dot gnu.org gcc-bugzilla@gcc.gnu.org
Mon Dec 4 17:37:00 GMT 2017


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83273

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |jason at gcc dot gnu.org,
                   |                            |nathan at gcc dot gnu.org

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
tree
finish_if_stmt_cond (tree cond, tree if_stmt)
{
  cond = maybe_convert_cond (cond);
  if (IF_STMT_CONSTEXPR_P (if_stmt)
      && is_constant_expression (cond)
      && !value_dependent_expression_p (cond))
    {
      cond = instantiate_non_dependent_expr (cond);
      cond = cxx_constant_value (cond, NULL_TREE);
    }

So, if is_constant_expression is true, we do the right thing.
There is just no diagnostics if cond fails the is_constant_expression check and
isn't value dependent.  We actually treat that if constexpr like normal if,
with both then and else evaluated.


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