RFC: C++ PATCH for c++/80831, ICE with -fsyntax-only

[Jason Merrill]

In this testcase, our c_parse_final_cleanups processing hits a
function that never got a cgraph node due to -fsyntax-only.  It seems
harmless to create one at this point; honza, does that make sense to
you?

Tested x86_64-pc-linux-gnu.

commit ccb40be7f9756533aeb658f092edd17ad0c7814e
Author: Jason Merrill <ja...@redhat.com>
Date:   Thu Jun 15 22:34:00 2017 -0400

            PR c++/80831 - ICE with -fsyntax-only.
    
            * decl2.c (c_parse_final_cleanups): Use cgraph_node::get_create.

diff --git a/gcc/cp/decl2.c b/gcc/cp/decl2.c
index ab32b71..3863736 100644
--- a/gcc/cp/decl2.c
+++ b/gcc/cp/decl2.c
@@ -4646,6 +4646,8 @@ c_parse_final_cleanups (void)
          if (!DECL_SAVED_TREE (decl))
            continue;
 
+         cgraph_node *node = cgraph_node::get_create (decl);
+
          /* We lie to the back end, pretending that some functions
             are not defined when they really are.  This keeps these
             functions from being put out unnecessarily.  But, we must
@@ -4666,9 +4668,6 @@ c_parse_final_cleanups (void)
              && DECL_INITIAL (decl)
              && decl_needed_p (decl))
            {
-             struct cgraph_node *node, *next;
-
-             node = cgraph_node::get (decl);
              if (node->cpp_implicit_alias)
                node = node->get_alias_target ();
 
@@ -4678,7 +4677,8 @@ c_parse_final_cleanups (void)
                 group, we need to mark all symbols in the same comdat group
                 that way.  */
              if (node->same_comdat_group)
-               for (next = dyn_cast<cgraph_node *> (node->same_comdat_group);
+               for (cgraph_node *next
+                      = dyn_cast<cgraph_node *> (node->same_comdat_group);
                     next != node;
                     next = dyn_cast<cgraph_node *> (next->same_comdat_group))
                  next->call_for_symbol_thunks_and_aliases (clear_decl_external,
@@ -4692,7 +4692,7 @@ c_parse_final_cleanups (void)
          if (!DECL_EXTERNAL (decl)
              && decl_needed_p (decl)
              && !TREE_ASM_WRITTEN (decl)
-             && !cgraph_node::get (decl)->definition)
+             && !node->definition)
            {
              /* We will output the function; no longer consider it in this
                 loop.  */
diff --git a/gcc/testsuite/g++.dg/other/fsyntax-only1.C 
b/gcc/testsuite/g++.dg/other/fsyntax-only1.C
new file mode 100644
index 0000000..19adb7e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/other/fsyntax-only1.C
@@ -0,0 +1,45 @@
+// PR c++/80831
+// { dg-options -fsyntax-only }
+// { dg-do compile { target c++11 } }
+
+class A
+{
+public:
+    virtual ~A() { }
+};
+
+class B { };
+
+class C : public A { };
+
+template<class J>
+class D : public C
+{
+public:
+    D() { }
+    ~D() { }
+};
+
+class E
+{
+public:
+    static E& p();
+    B q();
+    template<class J>
+    B q(void (J::*r)())
+    {
+        new D<J>();
+        return q();
+    }
+};
+
+void t()
+{
+  class F
+  {
+  public:
+    virtual void s() { }
+  };
+  E& x = E::p();
+  B y = x.q(&F::s);
+}