C++ PATCH for c++/84045, dependent typedefs and noexcept

[Jason Merrill]

This bug is a throwback to 50852 and such, where we treated a typedef
variant from dependent scope as equivalent to the underlying type,
which leads to crashes when we later try to instantiate that typedef
outside its scope.  To deal with that, I introduced strip_typedefs to
remove such offending typedefs from template arguments; it seems we
need to do the same things for exception-specifications.

Tested x86_64-pc-linux-gnu, applying to trunk.
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commit f98a61af4fc4d981b40eba7000bd3585003bf226
Author: Jason Merrill <jason@redhat.com>
Date:   Thu Feb 15 16:06:02 2018 -0500

            PR c++/84045 - ICE with typedef and noexcept.
            * except.c (build_noexcept_spec): Use strip_typedefs_expr.

diff --git a/gcc/cp/except.c b/gcc/cp/except.c
index 669bf9f6eaf..0b46698b974 100644
--- a/gcc/cp/except.c
+++ b/gcc/cp/except.c
@@ -1217,6 +1217,10 @@ build_noexcept_spec (tree expr, int complain)
     {
       gcc_assert (processing_template_decl
 		  || TREE_CODE (expr) == DEFERRED_NOEXCEPT);
+      if (TREE_CODE (expr) != DEFERRED_NOEXCEPT)
+	/* Avoid problems with a function type built with a dependent typedef
+	   being reused in another scope (c++/84045).  */
+	expr = strip_typedefs_expr (expr);
       return build_tree_list (expr, NULL_TREE);
     }
 }
diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept32.C b/gcc/testsuite/g++.dg/cpp0x/noexcept32.C
new file mode 100644
index 00000000000..9a435049599
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/noexcept32.C
@@ -0,0 +1,14 @@
+// PR c++/84045
+// { dg-do compile { target c++11 } }
+
+template <typename T> struct K {
+  static const bool d = true;
+};
+template <typename T, typename> struct B {
+  typedef K<T> D;
+  void foo () noexcept (D::d);
+};
+template <typename T> struct P {
+  P () noexcept (K<T>::d);
+};
+P<int> p;