[PATCH] c++, v2: Fix up mangling ICE with void{} [PR106863]

[Jakub Jelinek <jakub@redhat.com>]

On Thu, Oct 20, 2022 at 10:19:59AM -0400, Jason Merrill wrote:
> I think in a template we want the same early-return behavior as in the
> processing_template_decl block farther down in the function: specifically,
> we want to return a CONSTRUCTOR (for which COMPOUND_LITERAL_P is true), so
> it mangles as void{} rather than void().

So like this then?

2022-10-20  Jakub Jelinek  <jakub@redhat.com>

	PR c++/106863
	* semantics.cc (finish_compound_literal): For void{}, if
	processing_template_decl return a COMPOUND_LITERAL_P
	CONSTRUCTOR rather than void_node.

	* g++.dg/cpp0x/dr2351-2.C: New test.

--- gcc/cp/semantics.cc.jj	2022-10-19 01:14:58.343483355 +0200
+++ gcc/cp/semantics.cc	2022-10-20 16:32:30.605571968 +0200
@@ -3164,7 +3164,16 @@ finish_compound_literal (tree type, tree
     {
       /* DR2351 */
       if (VOID_TYPE_P (type) && CONSTRUCTOR_NELTS (compound_literal) == 0)
-	return void_node;
+	{
+	  if (!processing_template_decl)
+	    return void_node;
+	  TREE_TYPE (compound_literal) = type;
+	  TREE_HAS_CONSTRUCTOR (compound_literal) = 1;
+	  CONSTRUCTOR_IS_DEPENDENT (compound_literal) = 0;
+	  if (fcl_context == fcl_c99)
+	    CONSTRUCTOR_C99_COMPOUND_LITERAL (compound_literal) = 1;
+	  return compound_literal;
+	}
       else if (VOID_TYPE_P (type)
 	       && processing_template_decl
 	       && maybe_zero_constructor_nelts (compound_literal))
--- gcc/testsuite/g++.dg/cpp0x/dr2351-2.C.jj	2022-10-20 16:27:19.645821706 +0200
+++ gcc/testsuite/g++.dg/cpp0x/dr2351-2.C	2022-10-20 16:27:19.645821706 +0200
@@ -0,0 +1,16 @@
+// DR2351
+// { dg-do compile { target c++11 } }
+
+void bar (int);
+
+template <typename T>
+auto foo (T t) -> decltype (bar (t), void{})
+{
+  return bar (t);
+}
+
+int
+main ()
+{
+  foo (0);
+}


	Jakub