ipa-cp: Also look at self-recursive ancestor jump functions (PR122856)

PR 122856 shows that when looking at self recursive calls with
self-feeding jump functions, we did consider pass-through functions
but not ancestor functions with zero offsets.  This then leads to the
fact that constants which were collected from IPA-CP lattices were not
among those collected from available edges, triggering a verification
assert.

This patch fixes that by also detecting self-feeding ancestor jump
functions.

gcc/ChangeLog:

2026-02-06  Martin Jambor  <mjambor@suse.cz>

	PR ipa/122856
	* ipa-cp.cc (self_recursive_pass_through_p): Test jump function type first.
	(self_recursive_ancestor_p): New function.
	(find_scalar_values_for_callers_subset): Test also for self-recursive
	ancestor jump functions.
	(push_agg_values_for_index_from_edge): Likewise.

gcc/testsuite/ChangeLog:

2026-02-06  Martin Jambor  <mjambor@suse.cz>

	PR ipa/122856
	* g++.dg/ipa/pr122856.C: New test.

gcc/ipa-cp.cc

@@ -5259,9 +5259,9 @@ self_recursive_pass_through_p (cgraph_edge *cs, ipa_jump_func *jfunc, int i,
 			       bool simple = true)
 {
   enum availability availability;
-  if (cs->caller == cs->callee->function_symbol (&availability)
+  if (jfunc->type == IPA_JF_PASS_THROUGH
+      && cs->caller == cs->callee->function_symbol (&availability)
       && availability > AVAIL_INTERPOSABLE
-      && jfunc->type == IPA_JF_PASS_THROUGH
       && (!simple || ipa_get_jf_pass_through_operation (jfunc) == NOP_EXPR)
       && ipa_get_jf_pass_through_formal_id (jfunc) == i
       && ipa_node_params_sum->get (cs->caller)
@@ -5270,6 +5270,25 @@ self_recursive_pass_through_p (cgraph_edge *cs, ipa_jump_func *jfunc, int i,
   return false;
 }
 
+/* Return true if JFUNC, which describes the i-th parameter of call CS, is an
+   ancestor function with zero offset to itself when the cgraph_node involved
+   is not an IPA-CP clone.  */
+
+static bool
+self_recursive_ancestor_p (cgraph_edge *cs, ipa_jump_func *jfunc, int i)
+{
+  enum availability availability;
+  if (jfunc->type == IPA_JF_ANCESTOR
+      && cs->caller == cs->callee->function_symbol (&availability)
+      && availability > AVAIL_INTERPOSABLE
+      && ipa_get_jf_ancestor_offset (jfunc) == 0
+      && ipa_get_jf_ancestor_formal_id (jfunc) == i
+      && ipa_node_params_sum->get (cs->caller)
+      && !ipa_node_params_sum->get (cs->caller)->ipcp_orig_node)
+    return true;
+  return false;
+}
+
 /* Return true if JFUNC, which describes a part of an aggregate represented or
    pointed to by the i-th parameter of call CS, is a pass-through function to
    itself when the cgraph_node involved is not an IPA-CP clone..  When
@@ -5361,6 +5380,8 @@ find_scalar_values_for_callers_subset (vec<tree> &known_csts,
 				op_type);
 	      t = ipacp_value_safe_for_type (type, t);
 	    }
+	  else if (self_recursive_ancestor_p (cs, jump_func, i))
+	    continue;
 	  else
 	    t = ipa_value_from_jfunc (ipa_node_params_sum->get (cs->caller),
 				      jump_func, type);
@@ -5515,7 +5536,8 @@ push_agg_values_for_index_from_edge (struct cgraph_edge *cs, int index,
 	      && !src_plats->aggs_bottom
 	      && (agg_jf_preserved || !src_plats->aggs_by_ref))
 	    {
-	      if (interim && self_recursive_pass_through_p (cs, jfunc, index))
+	      if (interim && (self_recursive_pass_through_p (cs, jfunc, index)
+			      || self_recursive_ancestor_p (cs, jfunc, index)))
 		{
 		  interim->push_adjusted_values (src_idx, index, unit_delta,
 						 res);

gcc/testsuite/g++.dg/ipa/pr122856.C

@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -std=gnu++11" } */
+
+template <typename T>
+class Base {
+public:
+    virtual int get();
+    virtual ~Base() = default;
+};
+
+template <typename T>
+class Derived : public Base<T> {
+public:
+    int get() override { return Base<T>::get(); }
+};
+
+template <typename T>
+int Base<T>::get() {
+
+    return static_cast<Derived<int>*>(this)->get();
+}
+
+int main() {
+    Derived<int> d;
+    return d.get();
+}