c++: sizeof... mangling with alias template [PR95298]

We were getting sizeof... mangling wrong when the argument after
substitution was a pack expansion that is not a simple T..., such as
list<T>... in variadic-mangle4.C or (A+1)... in variadic-mangle5.C.  In the
former case we ICEd; in the latter case we wrongly mangled it as sZ
<expression>.

	PR c++/95298

gcc/cp/ChangeLog:

	* mangle.cc (write_expression): Handle v18 sizeof... bug.
	* pt.cc (tsubst_pack_expansion): Keep TREE_VEC for sizeof...
	(tsubst_expr): Don't strip TREE_VEC here.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/variadic-mangle2.C: Add non-member.
	* g++.dg/cpp0x/variadic-mangle4.C: New test.
	* g++.dg/cpp0x/variadic-mangle5.C: New test.
	* g++.dg/cpp0x/variadic-mangle5a.C: New test.

gcc/cp/mangle.cc

@@ -3444,6 +3444,7 @@ write_expression (tree expr)
 
       if (PACK_EXPANSION_P (op))
 	{
+    sizeof_pack:
 	  if (abi_check (11))
 	    {
 	      /* sZ rather than szDp.  */
@@ -3464,6 +3465,19 @@ write_expression (tree expr)
 	  int length = TREE_VEC_LENGTH (args);
 	  if (abi_check (10))
 	    {
+	      /* Before v19 we wrongly mangled all single pack expansions with
+		 sZ, but now only for expressions, as types ICEd (95298).  */
+	      if (length == 1)
+		{
+		  tree arg = TREE_VEC_ELT (args, 0);
+		  if (TREE_CODE (arg) == EXPR_PACK_EXPANSION
+		      && !abi_check (19))
+		    {
+		      op = arg;
+		      goto sizeof_pack;
+		    }
+		}
+
 	      /* sP <template-arg>* E # sizeof...(T), size of a captured
 		 template parameter pack from an alias template */
 	      write_string ("sP");

gcc/cp/pt.cc

@@ -13572,7 +13572,15 @@ tsubst_pack_expansion (tree t, tree args, tsubst_flags_t complain,
       /* If the argument pack is a single pack expansion, pull it out.  */
       if (TREE_VEC_LENGTH (args) == 1
 	  && pack_expansion_args_count (args))
-	return TREE_VEC_ELT (args, 0);
+	{
+	  tree arg = TREE_VEC_ELT (args, 0);
+	  if (PACK_EXPANSION_SIZEOF_P (t)
+	      && !TEMPLATE_PARM_P (PACK_EXPANSION_PATTERN (arg)))
+	    /* Except if this isn't a simple sizeof...(T) which gets sZ
+	       mangling, keep the TREE_VEC to get sP mangling.  */;
+	  else
+	    return TREE_VEC_ELT (args, 0);
+	}
 
       /* Types need no adjustment, nor does sizeof..., and if we still have
 	 some pack expansion args we won't do anything yet.  */
@@ -20261,8 +20269,6 @@ tsubst_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 	    {
 	      if (PACK_EXPANSION_P (expanded))
 		/* OK.  */;
-	      else if (TREE_VEC_LENGTH (expanded) == 1)
-		expanded = TREE_VEC_ELT (expanded, 0);
 	      else
 		expanded = make_argument_pack (expanded);
 

gcc/testsuite/g++.dg/cpp0x/variadic-mangle2.C

@@ -8,11 +8,19 @@ struct A {
   template<typename...T> using M = int[sizeof...(T)];
   template<typename...A> void g(M<A...> &);
 };
+
+template<typename ...T> using N = int[sizeof...(T)];
+template<typename ...T> void f(N<T...> &);
+// equivalent to template<typename ...T> void f(int(&)[sizeof...(T)])
+
 void g(A a)
 {
   int arr[3];
   // { dg-final { scan-assembler "_ZN1A1fIJLi1ELi2ELi3EEEEvRAsZT__i" } }
   a.f<1,2,3>(arr);
   // { dg-final { scan-assembler "_ZN1A1gIJiiiEEEvRAsZT__i" } }
   a.g<int,int,int>(arr);
+  // { dg-final { scan-assembler "_Z1fIJiiiEEvRAsZT__i" } }
+  f<int,int,int>(arr);
 }
+

gcc/testsuite/g++.dg/cpp0x/variadic-mangle4.C

@@ -0,0 +1,29 @@
+// PR c++/95298
+// { dg-do compile { target c++11 } }
+// { dg-additional-options -fabi-compat-version=0 }
+
+template<class...>
+struct list{};
+
+template<int n>
+struct _func_select
+{
+  using f = void;
+};
+
+struct func
+{
+  template<class... seqs>
+  using f = typename _func_select<sizeof...(seqs)>::f;
+};
+
+template<class... T>
+func::f<list<T>...> foo(T&&...)
+{}
+
+// { dg-final { scan-assembler "_Z3fooIJEEN12_func_selectIXsPDp4listIJT_EEEEE1fEDpOS2_" } }
+
+int main()
+{
+  foo();
+}

gcc/testsuite/g++.dg/cpp0x/variadic-mangle5.C

@@ -0,0 +1,13 @@
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-fabi-version=0 -fabi-compat-version=0" }
+
+template<int...T> using N = int[sizeof...(T)];
+template<int...A> void f(N<(A+1)...> &);
+
+void g()
+{
+  int arr[3];
+
+  // { dg-final { scan-assembler "_Z1fIJLi1ELi2ELi3EEEvRAsPXspplT_Li1EEE_i" } }
+  f<1,2,3>(arr);
+}

gcc/testsuite/g++.dg/cpp0x/variadic-mangle5a.C

@@ -0,0 +1,13 @@
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-fabi-version=18 -fabi-compat-version=18" }
+
+template<int...T> using N = int[sizeof...(T)];
+template<int...A> void f(N<(A+1)...> &);
+
+void g()
+{
+  int arr[3];
+
+  // { dg-final { scan-assembler "_Z1fIJLi1ELi2ELi3EEEvRAsZplT_Li1E_i" } }
+  f<1,2,3>(arr);
+}