merge revision(s) fb4cf204a662a8cd9dafef6f31f2bd0db9129abe,fa0279d947c3962c3f8c32852278d3ebb964cb19: [Backport #17725]

	use me->def instead of me for opt_table

	`vm_opt_method_table` is me=>bop table to manage the optimized
	methods (by specialized instruction). However, `me` can be invalidated
	to invalidate the method cache entry.
	[Bug #17725]

	To solve the issue, use `me-def` instead of `me` which simply copied
	at invalidation timing.

	A test by @jeremyevans https://github.com/ruby/ruby/pull/4376
	---
	 test/ruby/test_method.rb | 15 +++++++++++++++
	 vm.c                     | 11 +++++------
	 2 files changed, 20 insertions(+), 6 deletions(-)

	should not share same `def` for specialized method

	Because the key of redefine table is `def`, `def` should be
	unique for each optimized method (`alias` is not allowed).
	---
	 array.c | 2 +-
	 1 file changed, 1 insertion(+), 1 deletion(-)

1 files changed, 15 insertions, 0 deletions

diff --git a/test/ruby/test_method.rb b/test/ruby/test_method.rb
index 240821c9e2..0bd5dc63dd 100644
--- a/test/ruby/test_method.rb
+++ b/test/ruby/test_method.rb
@@ -1303,6 +1303,21 @@ class TestMethod < Test::Unit::TestCase
     end;
   end
 
+  def test_override_optimized_method_on_class_using_prepend
+    assert_separately(%w(--disable-gems), <<-'end;', timeout: 30)
+      # Bug #17725 [ruby-core:102884]
+      $VERBOSE = nil
+      String.prepend(Module.new)
+      class String
+        def + other
+          'blah blah'
+        end
+      end
+
+      assert_equal('blah blah', 'a' + 'b')
+    end;
+  end
+
   def test_eqq
     assert_operator(0.method(:<), :===, 5)
     assert_not_operator(0.method(:<), :===, -5)