Fix two ICEs with C++ destructors and LTO

[Jan Hubicka]

Hi,
these two PRs are about C++ destructors that are not virtual but have
virtual alias. The devirtualization machinery walks from alias to symbol
and is then confused by not knowing the class symbol belongs to.

I think it would make more sense to avoid these walks but that require
more of surgery, so for GCC9 I think it is best to stop freeing contexts
for desctructors. This does not save any stremaing because THIS pointer
of the destructor has the same type.

Bootstrapped/regtested x86_64-linux, OK?

Honza

	PR lto/87809
	PR lto/89335
	* tree.c (free_lang_data_in_decl): Do not free context of C++
	destrutors.

	* g++.dg/lto/pr87089_0.C: New testcase.
	* g++.dg/lto/pr87089_1.C: New testcase.
	* g++.dg/lto/pr89335_0.C: New testcase.
Index: tree.c
===================================================================
--- tree.c	(revision 269704)
+++ tree.c	(working copy)
@@ -5772,10 +5772,16 @@ free_lang_data_in_decl (tree decl, struc
      not do well with TREE_CHAIN pointers linking them.
 
      Also do not drop containing types for virtual methods and tables because
-     these are needed by devirtualization.  */
+     these are needed by devirtualization.
+     C++ destructors are special because C++ frontends sometimes produces
+     virtual destructor as an alias of non-virtual destructor.  In
+     devirutalization code we always walk through aliases and we need
+     context to be preserved too.  See PR89335  */
   if (TREE_CODE (decl) != FIELD_DECL
       && ((TREE_CODE (decl) != VAR_DECL && TREE_CODE (decl) != FUNCTION_DECL)
-          || !DECL_VIRTUAL_P (decl)))
+          || (!DECL_VIRTUAL_P (decl)
+	      && (TREE_CODE (decl) != FUNCTION_DECL
+		  || !DECL_CXX_DESTRUCTOR_P (decl)))))
     DECL_CONTEXT (decl) = fld_decl_context (DECL_CONTEXT (decl));
 }
 
Index: testsuite/g++.dg/lto/pr87089_0.C
===================================================================
--- testsuite/g++.dg/lto/pr87089_0.C	(nonexistent)
+++ testsuite/g++.dg/lto/pr87089_0.C	(working copy)
@@ -0,0 +1,21 @@
+// { dg-lto-do link }
+// { dg-extra-ld-options "-r -nostdlib -flinker-output=nolto-rel" }
+namespace itpp {
+template <class a> void b(a *c) { c[0].~a(); }
+class CFix;
+template <class> class d {
+  void e(const char *);
+  CFix *data;
+};
+class CFix {
+public:
+  virtual ~CFix();
+};
+template <> void d<int>::e(const char *) { b(data); }
+} // namespace itpp
+
+int
+main (void)
+{
+  return 0;
+}
Index: testsuite/g++.dg/lto/pr87089_1.C
===================================================================
--- testsuite/g++.dg/lto/pr87089_1.C	(nonexistent)
+++ testsuite/g++.dg/lto/pr87089_1.C	(working copy)
@@ -0,0 +1,12 @@
+namespace itpp {
+enum a { b };
+class CFix {
+public:
+  virtual ~CFix();
+};
+template <a = b> class c : CFix {
+  ~c() {}
+};
+template class c<>;
+} // namespace itpp
+
Index: testsuite/g++.dg/lto/pr89335_0.C
===================================================================
--- testsuite/g++.dg/lto/pr89335_0.C	(nonexistent)
+++ testsuite/g++.dg/lto/pr89335_0.C	(working copy)
@@ -0,0 +1,16 @@
+// { dg-lto-do link }
+// { dg-lto-options {{-O2 -flto -Wsuggest-final-methods}} }
+// { dg-extra-ld-options "-r -nostdlib -flinker-output=nolto-rel" }
+class Container
+{
+public:
+  virtual ~Container ();
+};
+class List : public Container // { dg-lto-message "final would enable devirtualization" }
+{
+};
+static List cache[256];
+int main (void)
+{
+  return 0;
+}