Remove impossible speculation in ipa_polymorphic_call_context::possible_dynamic_type_...

This patch makes ipa-cp dataflow monotone by making sure we do not use speculation that
was proved to be impossible earlier.

gcc/ChangeLog:

	PR ipa/123619
	* ipa-polymorphic-call.cc
	(ipa_polymorphic_call_context::possible_dynamic_type_change): Remove impossible
	speuculation.

diff --git a/gcc/ipa-polymorphic-call.cc b/gcc/ipa-polymorphic-call.cc
index 243a2f13cdc8dff23e3ac199f2db4ba7c02da1b7..5e53c217e33cee0db0b9c5a2a641ffa02f56dacb 100644 (file)
--- a/gcc/ipa-polymorphic-call.cc
+++ b/gcc/ipa-polymorphic-call.cc
@@ -2363,7 +2363,18 @@ ipa_polymorphic_call_context::possible_dynamic_type_change (bool in_poly_cdtor,
                                                            tree otr_type)
 {
   if (dynamic)
-    make_speculative (otr_type);
+    {
+      /* See if existing speculation was inconsistent before type change.
+        If so drop it first, so we do not lose track about it being
+        impossible.  */
+      if (speculative_outer_type
+         && !speculation_consistent_p (speculative_outer_type,
+                                       speculative_offset,
+                                       speculative_maybe_derived_type,
+                                       otr_type))
+       clear_speculation ();
+      make_speculative (otr_type);
+    }
   else if (in_poly_cdtor)
     maybe_in_construction = true;
 }