c: error for function with external and internal linkage [PR111708]

Declaring a function with both external and internal linkage
in the same TU is translation-time UB.  Add an error for this
case as already done for objects.

	PR c/111708

gcc/c/ChangeLog:

	* c-decl.cc (grokdeclarator): Add error.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr111708-1.c: New test.
	* gcc.dg/pr111708-2.c: New test.

3 files changed, 84 insertions, 0 deletions

diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
index 5822faf..0de3847 100644
--- a/gcc/c/c-decl.cc
+++ b/gcc/c/c-decl.cc
@@ -8032,6 +8032,27 @@ grokdeclarator (const struct c_declarator *declarator,
 		TREE_THIS_VOLATILE (decl) = 1;
 	      }
 	  }
+
+	/* C99 6.2.2p7: It is invalid (compile-time undefined
+	   behavior) to create an 'extern' declaration for a
+	   function if there is a global declaration that is
+	   'static' and the global declaration is not visible.
+	   (If the static declaration _is_ currently visible,
+	   the 'extern' declaration is taken to refer to that decl.) */
+	if (!initialized
+	    && TREE_PUBLIC (decl)
+	    && current_scope != file_scope)
+	  {
+	    tree global_decl  = identifier_global_value (declarator->u.id.id);
+	    tree visible_decl = lookup_name (declarator->u.id.id);
+
+	    if (global_decl
+		&& global_decl != visible_decl
+		&& VAR_OR_FUNCTION_DECL_P (global_decl)
+		&& !TREE_PUBLIC (global_decl))
+	      error_at (loc, "function previously declared %<static%> "
+			"redeclared %<extern%>");
+	  }
       }
     else
       {
diff --git a/gcc/testsuite/gcc.dg/pr111708-1.c b/gcc/testsuite/gcc.dg/pr111708-1.c
new file mode 100644
index 0000000..4af7f53
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr111708-1.c
@@ -0,0 +1,42 @@
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+extern int a(void);	// external linkage (6.2.2p4)
+static int a(void);	/* { dg-error "static declaration of 'a' follows non-static declaration" } */
+
+static int b(void);	// internal linkage (6.2.2p3)
+extern int b(void);	// internal linkage (6.2.2p4)
+
+static int h0(void);
+
+void s(void)
+{
+	extern int h0(void);	// internal linkage (6.2.2p4),
+	extern int h0(void); 	// internal linkage (6.2.2p4), redeclaration, ok
+	extern int h2(void);	// external linkage (6.2.2p4)
+	extern int h2(void);	// external linkage (6.2.2p4), redeclaration, ok.
+}
+
+
+extern int i(void);	// external linkage (6.2.2p4)
+static int j(void);	// internal linkage (6.2.2p3)
+
+void bar(void)
+{
+	extern int i(void);	// external linkage (6.2.2p4), ok
+}
+
+void foo(void)
+{
+	extern int j(void);	// internal linkage (6.2.2p4), ok, internal
+}
+
+void x(void)
+{
+	int i(void);		// no linkage (6.2.2p6)
+	int j;			// no linkage (6.2.2p6)
+	{
+		extern int j(void);	/* { dg-error "function previously declared 'static' redeclared 'extern'" } */
+	}
+}
+
diff --git a/gcc/testsuite/gcc.dg/pr111708-2.c b/gcc/testsuite/gcc.dg/pr111708-2.c
new file mode 100644
index 0000000..065c052
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr111708-2.c
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "" } */
+/* { dg-require-effective-target trampolines } */
+
+static void pp(void)
+{
+	int pp;
+	{
+		auto void pp(void);
+		void pp(void) { }
+	}
+}
+
+static void q2(void);
+
+static void qq(void)
+{
+	auto void q2(void);
+	void q2(void) { }
+}
+