ipa/120146 - deal with vanished varpool nodes in IPA PTA

I don't understand why they vanish when still refered to, but
lets deal with that in a conservative way.

	PR ipa/120146
	* tree-ssa-structalias.cc (create_variable_info_for): If
	the symtab cannot tell us whether all refs to a variable
	are explicit assume they are not.

	* g++.dg/ipa/pr120146.C: New testcase.

(cherry picked from commit b38e3a7196d25bc8bcb1fe55da7663745cea9470)

gcc/testsuite/g++.dg/ipa/pr120146.C

diff --git a/gcc/testsuite/g++.dg/ipa/pr120146.C b/gcc/testsuite/g++.dg/ipa/pr120146.C
new file mode 100644
index 0000000..33644b4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ipa/pr120146.C
@@ -0,0 +1,12 @@
+// { dg-do compile }
+// { dg-options "-O -fipa-pta" }
+
+struct basic_ios {
+  ~basic_ios();
+};
+struct basic_istream : virtual basic_ios {};
+template <typename> struct basic_ifstream : basic_istream {
+  template <typename _Path> basic_ifstream(_Path, int);
+};
+extern template class basic_ifstream<char>;
+void CompareFiles_path2() { basic_ifstream<char>(CompareFiles_path2, 0); }

gcc/tree-ssa-structalias.cc

diff --git a/gcc/tree-ssa-structalias.cc b/gcc/tree-ssa-structalias.cc
index 3ad0c69..deca44a 100644
--- a/gcc/tree-ssa-structalias.cc
+++ b/gcc/tree-ssa-structalias.cc
@@ -6562,7 +6562,7 @@
 	  varpool_node *vnode = varpool_node::get (decl);
 
 	  /* For escaped variables initialize them from nonlocal.  */
-	  if (!vnode->all_refs_explicit_p ())
+	  if (!vnode || !vnode->all_refs_explicit_p ())
 	    make_copy_constraint (vi, nonlocal_id);
 
 	  /* While we can in theory walk references for the varpool
@@ -6581,7 +6581,7 @@
 		process_constraint (new_constraint (lhs, *rhsp));
 	      /* If this is a variable that escapes from the unit
 		 the initializer escapes as well.  */
-	      if (!vnode->all_refs_explicit_p ())
+	      if (!vnode || !vnode->all_refs_explicit_p ())
 		{
 		  lhs.var = escaped_id;
 		  lhs.offset = 0;