commit d54ae54c13276adbfc5b27227a3630ad40002705
Author: Andrew MacLeod <amacleod@redhat.com>
Date:   Thu Mar 23 10:28:34 2023 -0400

    Ranger cache dominator queries should ignore backedges.
    
    When querying dominators for cache values, ignore back edges in
    read-only mode.
    
            PR tree-optimization/109238
            * gimple-range-cache.cc (ranger_cache::resolve_dom): Ignore
            predecessors which this block dominates.

diff --git a/gcc/gimple-range-cache.cc b/gcc/gimple-range-cache.cc
index 7aa6a3698cd..96460ece8f4 100644
--- a/gcc/gimple-range-cache.cc
+++ b/gcc/gimple-range-cache.cc
@@ -1510,6 +1510,11 @@ ranger_cache::resolve_dom (vrange &r, tree name, basic_block bb)
   Value_Range er (TREE_TYPE (name));
   FOR_EACH_EDGE (e, ei, bb->preds)
     {
+      // If the predecessor is dominated by this block, then there is a back
+      // edge, and won't provide anything useful.  We'll actually end up with
+      // VARYING as we will not resolve this node.
+      if (dominated_by_p (CDI_DOMINATORS, e->src, bb))
+	continue;
       edge_range (er, e, name, RFD_READ_ONLY);
       r.union_ (er);
     }