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

[Marek Polacek]

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  <pola...@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);
+      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