commit a87819b8f1b890d36a3f05bd9de80be20e9525dd
Author: Andrew MacLeod <amacleod@redhat.com>
Date:   Tue Oct 25 15:16:47 2022 -0400

    Check if varying may also be non-negative.
    
    When using strict enums, we can sometimes turn varying into a better
    range.
    
            * gimple-range-fold.cc (fold_using_range::fold_stmt): Check if
            stmt is non-negative and adjust the range.

diff --git a/gcc/gimple-range-fold.cc b/gcc/gimple-range-fold.cc
index f91923782dc..a899d8260b3 100644
--- a/gcc/gimple-range-fold.cc
+++ b/gcc/gimple-range-fold.cc
@@ -494,6 +494,14 @@ fold_using_range::fold_stmt (vrange &r, gimple *s, fur_source &src, tree name)
   else if (is_a<gassign *> (s) && gimple_assign_rhs_code (s) == COND_EXPR)
     res = range_of_cond_expr (r, as_a<gassign *> (s), src);
 
+  // If the result is varying, check for basic nonnegativeness.
+  // Specifically this helps for now with strict enum in cases like
+  // g++.dg/warn/pr33738.C.
+  bool so_p;
+  if (res && r.varying_p () && INTEGRAL_TYPE_P (r.type ())
+      && gimple_stmt_nonnegative_warnv_p (s, &so_p))
+    r.set_nonnegative (r.type ());
+
   if (!res)
     {
       // If no name specified or range is unsupported, bail.