G++ PATCH: -Wcast-align giving false positives

[Nathan Sidwell]

Jason Merrill wrote:
> OK.  My main point is that writing
> 
>  (TPL<Z> *) ptr
> 
> does not require TPL<Z> to be instantiated, and therefore it *must not* be
> instantiated if we want to call ourselves a C++ compiler.
You're correct, C++ does not _require_ the pointers to point to complete
types, but if the pointed to type is completable, it should be
(and a template type be instantiated).
If not, we won't be able to tell whether one is a base of the
other. The current code path for structure pointer conversions is
1) build_c_cast -> convert_force
2) convert_force -> convert_to_pointer_force
3) convert_to_pointer_force -> get_base_distance
4) get_base_distance -> complete_type
5) complete_type _attempts_ instantiation, but leaves things untouched
if no definition exists (if instantiation fails, we give an error)

get_base_distance contains the comment
  /* Should we be completing types here?  */

So I think the patch's attempt to complete the types in build_c_cast is
ok.

Attached is an augmented testcase which tried both TPL (completable template
type), and TPL2 (incompletable template type).

ok?

nathan

-- 
Dr Nathan Sidwell :: Computer Science Department :: Bristol University
Never hand someone a gun unless you are sure where they will point it
nathan@acm.org  http://www.cs.bris.ac.uk/~nathan/  nathan@cs.bris.ac.uk
// Build don't link:
// Skip if not target: sparc-*-*

// Special g++ Options: -ansi -pedantic-errors -Wcast-align

// Copyright (C) 1999 Free Software Foundation, Inc.
// Contributed by Nathan Sidwell 7 Dec 1999 <nathan@acm.org>

// converting a T * to void * does not need a complete T, and doesn't
// increase alignment requirements.

struct X;
struct Y;
struct Z {double m;};

void f3 (X *xp, Z *zp)
{
  (void *)xp;
  (void *)zp;
  (Y *)xp;
  (Y *)zp;
  (Z *)xp;
}

template <class T> struct TPL { T m;};
template <class T> struct TPL2;

void f4 (char *ptr)
{
  (Z *)ptr;           // WARNING - alignment
  (TPL<Z> *)ptr;      // WARNING - alignment
  (TPL2<Z> *)ptr;     // ok, incomplete
}