Re: More cases added to cast-qual-1.c test

[Geoff Keating <geoffk at cygnus dot com>]

"Kaveh R. Ghazi" <ghazi@caip.rutgers.edu> writes:

> I installed some more cases to the cast-qual-1.c test, they were
> inspired by bogus warnings from gcc sources when using -Wcast-qual.

I reverted this patch.

> +typedef struct rtx_def * rtx;
> +
> +void
> +typedef_cast(const void *bar)
> +{
> +  (const rtx)bar; /* { dg-bogus "cast discards" "discarding `const' warning" } */

A 'const rtx' is a pointer which has constant value, not a pointer
which points to something which has constant value.  Thus it is
perfectly correct to warn that a 'const void *' is being converted
into a 'struct rtx_def * const'.

The usual way to fix this is to do

typedef const struct rtx_def * const_rtx;

and to write

  (const_rtx) bar;

> +  (const rtx *)bar; /* { dg-warning "cast discards" "discarding `const' warning" } */

Here, it is not correct to warn, because we are casting a 'const void *'
to a 'struct rtx_def *const *', and both of these are pointers to things
declared 'const'.

> +}
> +
> +void
> +typedef_cast2(const rtx bar)
> +{
> +  (const void *)bar; /* { dg-bogus "cast discards" "discarding `const' warning" } */
> +  (const void **)bar; /* { dg-warning "cast discards" "discarding `const' warning" } */
> +}

Since the type pointed to by 'const rtx' is not constant, it's not
possible to discard any of its qualifiers by casting it :-).

So GCC is correct not to warn here.

> +void
> +typedef_assign(const void *bar)
> +{
> +  rtx const *foo1 = bar; /* { dg-bogus "initialization discards" "discarding `const' warning" } */
> +  const rtx *foo2 = bar; /* { dg-warning "initialization discards" "discarding `const' warning" } */
> +}

'rtx const' and 'const rtx' are the same type.  It doesn't matter
which order you write declaration-specifiers (except that things like
'int extern' are obsolecent).  Anyway, GCC is correct not to warn for
either of these, because 'bar' points to a 'const void' and 'foo1'
points to a 'const rtx'.

> +void
> +typdef_assign2(const rtx bar)
> +{
> +  void *const *foo1 = bar; /* { dg-bogus "initialization discards" "discarding `const' warning" } */
> +  const void **foo2 = bar; /* { dg-warning "initialization discards" "discarding `const' warning" } */
> +}

Here, GCC correctly complains that 'struct rtx_def' and 'void *' are
not compatible types, whether they are const or otherwise, which is
the more serious error.

-- 
- Geoffrey Keating <geoffk@cygnus.com>