C++ PATCH for c++/80150, ICE with overloaded variadic deduction

[Jason Merrill]

This bug is related to 69056, where I implemented deducing a pack that
starts with explicitly specified arguments.  In that patch I added a
sanity check to make sure that when we do that we always start from a
pack marked incomplete.  But this test demonstrates a case where that
check is wrong; if we're deducing the same pack from two different
function arguments, it isn't incomplete the second time, we need to
deduce the same thing we got the first time.

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

commit c46a927234d00a1723347ca1b21b2509f6513fc9
Author: Jason Merrill <ja...@redhat.com>
Date:   Thu Mar 23 13:29:35 2017 -0400

            PR c++/80150 - ICE with overloaded variadic deduction.
    
            * pt.c (try_one_overload): Remove asserts.

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index a4bf890..5259dad 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -19694,9 +19694,10 @@ try_one_overload (tree tparms,
             is equivalent to the corresponding explicitly specified argument.
             We may have deduced more arguments than were explicitly specified,
             and that's OK.  */
-         gcc_assert (ARGUMENT_PACK_INCOMPLETE_P (oldelt));
-         gcc_assert (ARGUMENT_PACK_ARGS (oldelt)
-                     == ARGUMENT_PACK_EXPLICIT_ARGS (oldelt));
+
+         /* We used to assert ARGUMENT_PACK_INCOMPLETE_P (oldelt) here, but
+            that's wrong if we deduce the same argument pack from multiple
+            function arguments: it's only incomplete the first time.  */
 
          tree explicit_pack = ARGUMENT_PACK_ARGS (oldelt);
          tree deduced_pack = ARGUMENT_PACK_ARGS (elt);
diff --git a/gcc/testsuite/g++.dg/cpp0x/variadic-unify-3.C 
b/gcc/testsuite/g++.dg/cpp0x/variadic-unify-3.C
new file mode 100644
index 0000000..45f4d63
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/variadic-unify-3.C
@@ -0,0 +1,20 @@
+// PR c++/80150
+// { dg-do compile { target c++11 } }
+
+template <typename R, typename... Args>
+bool compare_functions(R(*funcA)(Args...), R(*funcB)(Args...), Args... args) {
+  return false;
+}
+
+int foo(int x) {
+  return x;
+}
+
+float foo(float x) {
+ return x;
+}
+
+int main() {
+  int a = 10;
+  compare_functions<int>(foo, foo, a);
+}