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

[Jason Merrill <jason at redhat dot com>]

On 01/22/2016 05:07 PM, Marek Polacek wrote:
> 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);

Well, a reinterpret_cast makes the expression non-constant, so we can 
recognize that case (when the types are unrelated) and bail out.  After 
that we probably still need to deal with the case of conversion to a 
pointer-to-member-of-base type; for functions it looks like we can just 
copy the PTRMEM_CST and give it a different type, but for data members I 
think we'll need to add support for the type not matching the member in 
expand_ptrmem_cst.

Jason