C PATCH to reject va_arg (ap, void) (PR c/65901)

As reported in the PR, va_arg (ap, void) probably doesn't make any sense and
should be rejected thus.  cc1plus and clang reject va_arg with an incomplete
type.  This patch makes cc1 reject it as well.

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2015-04-27  Marek Polacek  <polacek@redhat.com>

	PR c/65901
	* c-typeck.c (c_build_va_arg): Require TYPE be a complete type.

	* gcc.c-torture/compile/pr48767.c (foo): Add dg-error.
	* gcc.dg/pr65901.c: New test.


	Marek

On 04/27/2015 11:30 AM, Marek Polacek wrote:
> As reported in the PR, va_arg (ap, void) probably doesn't make any sense and
> should be rejected thus.  cc1plus and clang reject va_arg with an incomplete
> type.  This patch makes cc1 reject it as well.
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>
> 2015-04-27  Marek Polacek  <polacek@redhat.com>
>
> 	PR c/65901
> 	* c-typeck.c (c_build_va_arg): Require TYPE be a complete type.
>
> 	* gcc.c-torture/compile/pr48767.c (foo): Add dg-error.
> 	* gcc.dg/pr65901.c: New test.
OK.
jeff

On 04/27/2015 11:30 AM, Marek Polacek wrote:
> As reported in the PR, va_arg (ap, void) probably doesn't make any sense and
> should be rejected thus.  cc1plus and clang reject va_arg with an incomplete
> type.  This patch makes cc1 reject it as well.
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>
> 2015-04-27  Marek Polacek  <polacek@redhat.com>
>
> 	PR c/65901
> 	* c-typeck.c (c_build_va_arg): Require TYPE be a complete type.
>
> 	* gcc.c-torture/compile/pr48767.c (foo): Add dg-error.
> 	* gcc.dg/pr65901.c: New test.
>
> diff --git gcc/c/c-typeck.c gcc/c/c-typeck.c
> index 91735b5..c58e918 100644
> --- gcc/c/c-typeck.c
> +++ gcc/c/c-typeck.c
> @@ -12648,6 +12648,11 @@ c_build_va_arg (location_t loc, tree expr, tree type)
>     if (warn_cxx_compat && TREE_CODE (type) == ENUMERAL_TYPE)
>       warning_at (loc, OPT_Wc___compat,
>   		"C++ requires promoted type, not enum type, in %<va_arg%>");
> +  if (type == error_mark_node || !COMPLETE_TYPE_P (type))
> +    {
> +      c_incomplete_type_error (NULL_TREE, type);

The error message in the test cases below isn't quite right.
The type of the aggregates isn't undefined, it's incomplete.
Looking at the function, I wonder if the first argument
should be EXPR rather than than NULL_TREE? Alternatively,
experimenting with other cases where GCC diagnoses invalid
uses of incomplete type, I see that it issues:

   "invalid application of %qs to incomplete type %qT"

which might work even better here since we could name the
expression (va_arg).

Martin

> +      return error_mark_node;
> +    }
>     return build_va_arg (loc, expr, type);
>   }
>
> diff --git gcc/testsuite/gcc.c-torture/compile/pr48767.c gcc/testsuite/gcc.c-torture/compile/pr48767.c
> index 66cb348..c8fef35 100644
> --- gcc/testsuite/gcc.c-torture/compile/pr48767.c
> +++ gcc/testsuite/gcc.c-torture/compile/pr48767.c
> @@ -3,5 +3,5 @@
>   void
>   foo (__builtin_va_list ap)
>   {
> -  __builtin_va_arg (ap, void);
> +  __builtin_va_arg (ap, void);  /* { dg-error "invalid use of void expression" } */
>   }
> diff --git gcc/testsuite/gcc.dg/pr65901.c gcc/testsuite/gcc.dg/pr65901.c
> index e69de29..8708a1e 100644
> --- gcc/testsuite/gcc.dg/pr65901.c
> +++ gcc/testsuite/gcc.dg/pr65901.c
> @@ -0,0 +1,16 @@
> +/* PR c/65901 */
> +/* { dg-do compile } */
> +/* { dg-options "" } */
> +
> +struct S;
> +enum E;
> +union U;
> +
> +void
> +foo (__builtin_va_list ap)
> +{
> +  __builtin_va_arg (ap, void);  /* { dg-error "invalid use of void expression" } */
> +  __builtin_va_arg (ap, struct S);  /* { dg-error "invalid use of undefined type" } */
> +  __builtin_va_arg (ap, enum E);  /* { dg-error "invalid use of undefined type" } */
> +  __builtin_va_arg (ap, union U);  /* { dg-error "invalid use of undefined type" } */
> +}
>
> 	Marek
>