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c++: Defer cloning to post-loading [PR 99170]

Message ID 1686b445-8a32-0be6-614e-70202c281aab@acm.org
State New
Headers show
Series c++: Defer cloning to post-loading [PR 99170] | expand

Commit Message

Nathan Sidwell March 3, 2021, 8:45 p.m. UTC
It turns out that cloning can cause use to load things. Specifically 
when checking paramter shadows (this is avoidable), and also the delete 
operator of a deleting dtor (not avoidable).  Doing that in the middle 
of loading is a bad thing.  This defers it to a post-load worklist.  If 
it causes more loading at that point there is no problem, as we've 
completed the first set of loads, bar this bit of cleanup.

Again, this doesn't fix 99170, but is a step towards a solution.

         PR c++/99170
         gcc/cp/
         * module.cc (post_load_decls): New.
         (lazy_snum, recursive_lazy): Move earlier.
         (module_state::read_cluster): Push cloning onto post_load_decls.
         (post_load_processing): New.  Do the cloning here.
         (module_state::read_inits): Call post_load_processing.
         (module_state::read_language): Likewise.
         (lazy_load_binding, lazy_load_specializations): Likewise
         (lazy_load_members): Likewise
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Patch

diff --git c/gcc/cp/module.cc w/gcc/cp/module.cc
index b068acea3bd..b7b9c3734f2 100644
--- c/gcc/cp/module.cc
+++ w/gcc/cp/module.cc
@@ -2644,6 +2644,10 @@  depset *depset::make_entity (tree entity, entity_kind ek, bool is_defn)
   return r;
 }
 
+/* Decls that need some post processing once a batch of lazy loads has
+   completed.  */
+vec<tree, va_heap, vl_embed> *post_load_decls;
+
 /* Values keyed to some unsigned integer.  This is not GTY'd, so if
    T is tree they must be reachable via some other path.  */
 
@@ -14023,6 +14027,21 @@  make_mapper (location_t loc)
   return mapper;
 }
 
+static unsigned lazy_snum;
+
+static bool
+recursive_lazy (unsigned snum = ~0u)
+{
+  if (lazy_snum)
+    {
+      error_at (input_location, "recursive lazy load");
+      return true;
+    }
+
+  lazy_snum = snum;
+  return false;
+}
+
 /* If THIS is the current purview, issue an import error and return false.  */
 
 bool
@@ -15016,11 +15035,7 @@  module_state::read_cluster (unsigned snum)
       if (abstract)
 	;
       else if (DECL_ABSTRACT_P (decl))
-	{
-	  bool cloned = maybe_clone_body (decl);
-	  if (!cloned)
-	    from ()->set_error ();
-	}
+	vec_safe_push (post_load_decls, decl);
       else
 	{
 	  bool aggr = aggregate_value_p (DECL_RESULT (decl), decl);
@@ -17267,6 +17282,33 @@  module_state::write_inits (elf_out *to, depset::hash &table, unsigned *crc_ptr)
   return count;
 }
 
+/* We have to defer some post-load processing until we've completed
+   reading, because they can cause more reading.  */
+
+static void
+post_load_processing ()
+{
+  if (!post_load_decls)
+    return;
+
+  tree old_cfd = current_function_decl;
+  struct function *old_cfun = cfun;
+  while (post_load_decls->length ())
+    {
+      tree decl = post_load_decls->pop ();
+
+      dump () && dump ("Post-load processing of %N", decl);
+
+      gcc_checking_assert (DECL_ABSTRACT_P (decl));
+      /* Cloning can cause loading -- specifically operator delete for
+	 the deleting dtor.  */
+      maybe_clone_body (decl);
+    }
+
+  cfun = old_cfun;
+  current_function_decl = old_cfd;
+}
+
 bool
 module_state::read_inits (unsigned count)
 {
@@ -17276,6 +17318,7 @@  module_state::read_inits (unsigned count)
   dump () && dump ("Reading %u initializers", count);
   dump.indent ();
 
+  lazy_snum = ~0u;
   for (unsigned ix = 0; ix != count; ix++)
     {
       /* Merely referencing the decl causes its initializer to be read
@@ -17287,6 +17330,8 @@  module_state::read_inits (unsigned count)
       if (decl)
 	dump ("Initializer:%u for %N", count, decl);
     }
+  lazy_snum = 0;
+  post_load_processing ();
   dump.outdent ();
   if (!sec.end (from ()))
     return false;  
@@ -18025,21 +18070,6 @@  module_state::read_preprocessor (bool outermost)
   return check_read (outermost, ok);
 }
 
-static unsigned lazy_snum;
-
-static bool
-recursive_lazy (unsigned snum = ~0u)
-{
-  if (lazy_snum)
-    {
-      error_at (input_location, "recursive lazy load");
-      return true;
-    }
-
-  lazy_snum = snum;
-  return false;
-}
-
 /* Read language state.  */
 
 bool
@@ -18114,16 +18144,15 @@  module_state::read_language (bool outermost)
 
       unsigned hwm = counts[MSC_sec_hwm];
       for (unsigned ix = counts[MSC_sec_lwm]; ok && ix != hwm; ix++)
-	{
-	  if (!load_section (ix, NULL))
-	    {
-	      ok = false;
-	      break;
-	    }
-	  ggc_collect ();
-	}
-
+	if (!load_section (ix, NULL))
+	  {
+	    ok = false;
+	    break;
+	  }
       lazy_snum = 0;
+      post_load_processing ();
+
+      ggc_collect ();
 
       if (ok && CHECKING_P)
 	for (unsigned ix = 0; ix != entity_num; ix++)
@@ -18873,6 +18902,7 @@  lazy_load_binding (unsigned mod, tree ns, tree id, binding_slot *mslot)
     {
       ok = module->load_section (snum, mslot);
       lazy_snum = 0;
+      post_load_processing ();
     }
 
   dump.pop (n);
@@ -18929,6 +18959,7 @@  lazy_load_specializations (tree tmpl)
 	  function_depth--;
 	}
       lazy_snum = 0;
+      post_load_processing ();
     }
 
   timevar_stop (TV_MODULE_IMPORT);
@@ -18969,6 +19000,7 @@  lazy_load_members (tree decl)
 		       set->num, import_entity_module (ident),
 		       ident - import_entity_module (ident)->entity_lwm, decl);
       pendset_lazy_load (set, false);
+      post_load_processing ();
       dump.pop (n);
 
       function_depth--;