diff --git a/bootstraptest/test_method.rb b/bootstraptest/test_method.rb
index 04c9eb2d11425e..964bf39d98b801 100644
--- a/bootstraptest/test_method.rb
+++ b/bootstraptest/test_method.rb
@@ -1190,3 +1190,12 @@ def test2 o, args, block
   test2 o1, [], block
   $result.join
 }
+
+assert_equal 'ok', %q{
+  def foo
+    binding
+    ["ok"].first
+  end
+  foo
+  foo
+}, '[Bug #20178]'
diff --git a/ext/socket/extconf.rb b/ext/socket/extconf.rb
index 544bed5298cfc6..4e8536fc606bc0 100644
--- a/ext/socket/extconf.rb
+++ b/ext/socket/extconf.rb
@@ -706,8 +706,6 @@ def %(s) s || self end
 
   have_func("pthread_create")
   have_func("pthread_detach")
-  have_func("pthread_attr_setaffinity_np")
-  have_func("sched_getcpu")
 
   $VPATH << '$(topdir)' << '$(top_srcdir)'
   create_makefile("socket")
diff --git a/ext/socket/raddrinfo.c b/ext/socket/raddrinfo.c
index 9747f940369967..560312741f6820 100644
--- a/ext/socket/raddrinfo.c
+++ b/ext/socket/raddrinfo.c
@@ -461,7 +461,7 @@ cancel_getaddrinfo(void *ptr)
 }
 
 static int
-do_pthread_create(pthread_t *th, const pthread_attr_t *attr, void *(*start_routine) (void *), void *arg)
+do_pthread_create(pthread_t *th, void *(*start_routine) (void *), void *arg)
 {
     int limit = 3, ret;
     do {
@@ -469,7 +469,7 @@ do_pthread_create(pthread_t *th, const pthread_attr_t *attr, void *(*start_routi
         //
         // https://bugs.openjdk.org/browse/JDK-8268605
         // https://github.com/openjdk/jdk/commit/e35005d5ce383ddd108096a3079b17cb0bcf76f1
-        ret = pthread_create(th, attr, start_routine, arg);
+        ret = pthread_create(th, 0, start_routine, arg);
     } while (ret == EAGAIN && limit-- > 0);
     return ret;
 }
@@ -489,23 +489,8 @@ rb_getaddrinfo(const char *hostp, const char *portp, const struct addrinfo *hint
         return EAI_MEMORY;
     }
 
-    pthread_attr_t attr;
-    if (pthread_attr_init(&attr) != 0) {
-        free_getaddrinfo_arg(arg);
-        return EAI_AGAIN;
-    }
-#if defined(HAVE_PTHREAD_ATTR_SETAFFINITY_NP) && defined(HAVE_SCHED_GETCPU)
-    cpu_set_t tmp_cpu_set;
-    CPU_ZERO(&tmp_cpu_set);
-    int cpu = sched_getcpu();
-    if (cpu < CPU_SETSIZE) {
-        CPU_SET(cpu, &tmp_cpu_set);
-        pthread_attr_setaffinity_np(&attr, sizeof(cpu_set_t), &tmp_cpu_set);
-    }
-#endif
-
     pthread_t th;
-    if (do_pthread_create(&th, &attr, do_getaddrinfo, arg) != 0) {
+    if (do_pthread_create(&th, do_getaddrinfo, arg) != 0) {
         free_getaddrinfo_arg(arg);
         return EAI_AGAIN;
     }
@@ -716,23 +701,8 @@ rb_getnameinfo(const struct sockaddr *sa, socklen_t salen,
         return EAI_MEMORY;
     }
 
-    pthread_attr_t attr;
-    if (pthread_attr_init(&attr) != 0) {
-        free_getnameinfo_arg(arg);
-        return EAI_AGAIN;
-    }
-#if defined(HAVE_PTHREAD_ATTR_SETAFFINITY_NP) && defined(HAVE_SCHED_GETCPU)
-    cpu_set_t tmp_cpu_set;
-    CPU_ZERO(&tmp_cpu_set);
-    int cpu = sched_getcpu();
-    if (cpu < CPU_SETSIZE) {
-        CPU_SET(cpu, &tmp_cpu_set);
-        pthread_attr_setaffinity_np(&attr, sizeof(cpu_set_t), &tmp_cpu_set);
-    }
-#endif
-
     pthread_t th;
-    if (do_pthread_create(&th, 0, do_getnameinfo, arg) != 0) {
+    if (do_pthread_create(&th, do_getnameinfo, arg) != 0) {
         free_getnameinfo_arg(arg);
         return EAI_AGAIN;
     }
diff --git a/hash.c b/hash.c
index 78e9d9a2d60c8b..b15d856ee19c36 100644
--- a/hash.c
+++ b/hash.c
@@ -1557,7 +1557,15 @@ hash_copy(VALUE ret, VALUE hash)
 static VALUE
 hash_dup_with_compare_by_id(VALUE hash)
 {
-    return hash_copy(copy_compare_by_id(rb_hash_new(), hash), hash);
+    VALUE dup = hash_alloc_flags(rb_cHash, 0, Qnil, RHASH_ST_TABLE_P(hash));
+    if (RHASH_ST_TABLE_P(hash)) {
+        RHASH_SET_ST_FLAG(dup);
+    }
+    else {
+        RHASH_UNSET_ST_FLAG(dup);
+    }
+
+    return hash_copy(dup, hash);
 }
 
 static VALUE
diff --git a/test/ruby/test_hash.rb b/test/ruby/test_hash.rb
index 70daea0ef19150..c72b256bab39aa 100644
--- a/test/ruby/test_hash.rb
+++ b/test/ruby/test_hash.rb
@@ -1458,6 +1458,16 @@ def test_compare_by_identity
     assert_predicate(h.dup, :compare_by_identity?, bug8703)
   end
 
+  def test_compare_by_identy_memory_leak
+    assert_no_memory_leak([], "", "#{<<~"begin;"}\n#{<<~'end;'}", "[Bug #20145]", rss: true)
+    begin;
+      h = { 1 => 2 }.compare_by_identity
+      1_000_000.times do
+        h.select { false }
+      end
+    end;
+  end
+
   def test_same_key
     bug9646 = '[ruby-dev:48047] [Bug #9646] Infinite loop at Hash#each'
     h = @cls[a=[], 1]
diff --git a/tool/mk_builtin_loader.rb b/tool/mk_builtin_loader.rb
index 5ab427ca9b2931..95600e6a3bdc55 100644
--- a/tool/mk_builtin_loader.rb
+++ b/tool/mk_builtin_loader.rb
@@ -263,11 +263,17 @@ def collect_iseq iseq_ary
 
 def generate_cexpr(ofile, lineno, line_file, body_lineno, text, locals, func_name)
   f = StringIO.new
+
+  # Avoid generating fetches of lvars we don't need. This is imperfect as it
+  # will match text inside strings or other false positives.
+  local_candidates = text.scan(/[a-zA-Z_][a-zA-Z0-9_]*/)
+
   f.puts '{'
   lineno += 1
   # locals is nil outside methods
   locals&.reverse_each&.with_index{|param, i|
     next unless Symbol === param
+    next unless local_candidates.include?(param.to_s)
     f.puts "MAYBE_UNUSED(const VALUE) #{param} = rb_vm_lvar(ec, #{-3 - i});"
     lineno += 1
   }