C++ PATCH for c++/80174, ICE with partial specialization of member template

C++ PATCH for c++/80174, ICE with partial specialization of member template

[Jason Merrill]

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My patch for 71747 missed this case; we only want to consider the
innermost args in the call to coerce_template_parms, just like in
unification and comparison.

Tested x86_64-pc-linux-gnu, applying to trunk and 7.

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commit 33e24de5519e868a915ccee6fcfee362870930f6
Author: Jason Merrill <jason@redhat.com>
Date:   Thu Jun 15 18:00:47 2017 -0400

            PR c++/80174 - ICE with partial specialization of member template.
    
            PR c++/71747
            * pt.c (get_partial_spec_bindings): Only coerce innermost args.

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 8a61b74..b055507 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -21676,9 +21676,11 @@ get_partial_spec_bindings (tree tmpl, tree spec_tmpl, tree args)
      `T' is `A' but unify () does not check whether `typename T::X'
      is `int'.  */
   spec_args = tsubst (spec_args, deduced_args, tf_none, NULL_TREE);
-  spec_args = coerce_template_parms (DECL_INNERMOST_TEMPLATE_PARMS (tmpl),
-				     spec_args, tmpl,
-				     tf_none, false, false);
+
+  if (spec_args != error_mark_node)
+    spec_args = coerce_template_parms (DECL_INNERMOST_TEMPLATE_PARMS (tmpl),
+				       INNERMOST_TEMPLATE_ARGS (spec_args),
+				       tmpl, tf_none, false, false);
 
   pop_tinst_level ();
 
diff --git a/gcc/testsuite/g++.dg/template/partial-specialization6.C b/gcc/testsuite/g++.dg/template/partial-specialization6.C
new file mode 100644
index 0000000..51a1590
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/partial-specialization6.C
@@ -0,0 +1,28 @@
+// PR c++/80174
+
+typedef unsigned char uint8_t; 
+
+template <typename T>
+struct HighestMaxFieldIdx {
+  static const uint8_t maxFieldIdx = T::fieldIdx;
+};
+
+template <typename This>
+struct Outer {
+
+  template <uint8_t _fieldIdx, typename T, T This::*field>
+  struct Varint {};
+
+
+  template <uint8_t _fieldIdx, uint8_t This::*field>
+  struct Varint<_fieldIdx, uint8_t, field> {
+    static const uint8_t fieldIdx = _fieldIdx;
+  };
+};
+
+struct Msg {
+  uint8_t a;
+
+  static const uint8_t t
+  = HighestMaxFieldIdx<Outer<Msg>::Varint<1, uint8_t, &Msg::a> >::maxFieldIdx;
+};