[C++ PATCH] PR c++/89761 - ICE with sizeof... in pack expansion.

[C++ PATCH] PR c++/89761 - ICE with sizeof... in pack expansion.

[Jason Merrill]

In this testcase we get confused when looking at the sizeof... because the
argument pack for 'args' has been wrapped in an ARGUMENT_PACK_SELECT as part
of expanding the fold-expression.  We handle this situation a bit lower down
in tsubst_pack_expansion, but that doesn't help the call to
argument_pack_element_is_expansion_p, which happens earlier.

Tested x86_64-pc-linux-gnu, applying to trunk.

	* pt.c (argument_pack_element_is_expansion_p): Handle
	ARGUMENT_PACK_SELECT.
---
 gcc/cp/pt.c                         |  3 +++
 gcc/testsuite/g++.dg/cpp1z/fold10.C | 17 +++++++++++++++++
 gcc/cp/ChangeLog                    |  4 ++++
 3 files changed, 24 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp1z/fold10.C

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 7dc6e44cf7b..0acc16d1b92 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -11544,6 +11544,9 @@ make_fnparm_pack (tree spec_parm)
 static int
 argument_pack_element_is_expansion_p (tree arg_pack, int i)
 {
+  if (TREE_CODE (arg_pack) == ARGUMENT_PACK_SELECT)
+    /* We're being called before this happens in tsubst_pack_expansion.  */
+    arg_pack = ARGUMENT_PACK_SELECT_FROM_PACK (arg_pack);
   tree vec = ARGUMENT_PACK_ARGS (arg_pack);
   if (i >= TREE_VEC_LENGTH (vec))
     return 0;
diff --git a/gcc/testsuite/g++.dg/cpp1z/fold10.C b/gcc/testsuite/g++.dg/cpp1z/fold10.C
new file mode 100644
index 00000000000..1bd39a05400
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/fold10.C
@@ -0,0 +1,17 @@
+// PR c++/89761
+// { dg-do compile { target c++17 } }
+
+template <int...> struct seq {};
+template <bool> struct S {
+    template <typename Args>
+    constexpr static void call(Args&&...) {}
+};
+
+template <int ...Idx,typename ...Args>
+auto foo (seq<Idx...>, Args&& ...args) {
+    return (S<Idx==sizeof...(args)>::call(args), ...);
+}
+
+void bar() {
+    foo(seq<0,1,2>{}, 1,2,3);
+}
diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index a3341bd9672..d4dc5d7146a 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,5 +1,9 @@
 2019-03-18  Jason Merrill  <jason@redhat.com>
 
+	PR c++/89761 - ICE with sizeof... in pack expansion.
+	* pt.c (argument_pack_element_is_expansion_p): Handle
+	ARGUMENT_PACK_SELECT.
+
 	PR c++/89640 - GNU attributes on lambda.
 	* parser.c (cp_parser_lambda_declarator_opt): Allow GNU attributes.
 

base-commit: 4273f1242040771577874bf759fd41b31db5773a
-- 
2.20.1