Re: C++ PATCH for c++/69379 (ICE with PTRMEM_CST wrapped in NOP_EXPR)

[Marek Polacek]

On Fri, Jan 22, 2016 at 03:38:26PM -0500, Jason Merrill wrote:
> If we have a NOP_EXPR to the same type, we should strip it here.

This helps for the unreduced testcases in the PR, but not for the reduced one,
because for the reduced one, the types are not the same.  One type is
struct 
{
  void Dict::<T461> (struct Dict *, T) * __pfn;
  long int __delta;
}
and the second one
struct 
{
  void Dict::<T442> (struct Dict *) * __pfn;
  long int __delta;
}

The NOP_EXPR in this case originated in build_reinterpret_cast_1:
7070   else if ((TYPE_PTRFN_P (type) && TYPE_PTRFN_P (intype))
7071            || (TYPE_PTRMEMFUNC_P (type) && TYPE_PTRMEMFUNC_P (intype)))
7072     return build_nop (type, expr);

So maybe the following patch is desirable, but it's not a complete fix :(.
Thanks,

2016-01-22  Marek Polacek  <pola...@redhat.com>

        PR c++/69379
        * constexpr.c (cxx_eval_constant_expression) [NOP_EXPR]: When
        converting PTRMEM_CST to the same type, strip nops.

diff --git gcc/cp/constexpr.c gcc/cp/constexpr.c
index 6b0e5a8..6fe5cbe 100644
--- gcc/cp/constexpr.c
+++ gcc/cp/constexpr.c
@@ -3619,6 +3619,11 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, 
tree t,
        if (TREE_CODE (op) == PTRMEM_CST
            && !TYPE_PTRMEM_P (type))
          op = cplus_expand_constant (op);
+       if (TREE_CODE (op) == PTRMEM_CST
+           && tcode == NOP_EXPR
+           && same_type_ignoring_top_level_qualifiers_p (type,
+                                                         TREE_TYPE (op)))
+         STRIP_NOPS (t);
        if (POINTER_TYPE_P (type)
            && TREE_CODE (op) == INTEGER_CST
            && !integer_zerop (op))

        Marek