5 files changed, 27 insertions, 1 deletions
diff --git a/compile.c b/compile.c
index e3d66b6809..317475b525 100644
--- a/compile.c
+++ b/compile.c
@@ -5211,7 +5211,12 @@ iseq_compile_each0(rb_iseq_t *iseq, LINK_ANCHOR *const ret, NODE *node, int popp
 	    ISEQ_COMPILE_DATA(iseq)->option->specialized_instruction) {
 	    VALUE str = rb_fstring(node->nd_recv->nd_lit);
 	    iseq_add_mark_object(iseq, str);
-	    ADD_INSN1(ret, line, opt_str_freeze, str);
+	    if (node->nd_mid == idUMinus) {
+		ADD_INSN1(ret, line, opt_str_uminus, str);
+	    }
+	    else {
+		ADD_INSN1(ret, line, opt_str_freeze, str);
+	    }
 	    if (popped) {
 		ADD_INSN(ret, line, pop);
 	    }
diff --git a/insns.def b/insns.def
index 9bae14b5a9..a4f2526bef 100644
--- a/insns.def
+++ b/insns.def
@@ -982,6 +982,20 @@ opt_str_freeze
 }
 
 DEFINE_INSN
+opt_str_uminus
+(VALUE str)
+()
+(VALUE val)
+{
+    if (BASIC_OP_UNREDEFINED_P(BOP_UMINUS, STRING_REDEFINED_OP_FLAG)) {
+	val = str;
+    }
+    else {
+	val = rb_funcall(rb_str_resurrect(str), idUMinus, 0);
+    }
+}
+
+DEFINE_INSN
 opt_newarray_max
 (rb_num_t num)
 (...)
diff --git a/test/ruby/test_optimization.rb b/test/ruby/test_optimization.rb
index 502d12389e..7c8990fde8 100644
--- a/test/ruby/test_optimization.rb
+++ b/test/ruby/test_optimization.rb
@@ -104,6 +104,11 @@ class TestRubyOptimization < Test::Unit::TestCase
     assert_redefine_method('String', 'freeze', 'assert_nil "foo".freeze')
   end
 
+  def test_string_uminus
+    assert_same "foo".freeze, -"foo"
+    assert_redefine_method('String', '-@', 'assert_nil(-"foo")')
+  end
+
   def test_string_freeze_saves_memory
     n = 16384
     data = '.'.freeze
diff --git a/vm.c b/vm.c
index 1eefee18a6..9ece1b8c3d 100644
--- a/vm.c
+++ b/vm.c
@@ -1569,6 +1569,7 @@ vm_init_redefined_flag(void)
     OP(Succ, SUCC), (C(Integer), C(String), C(Time));
     OP(EqTilde, MATCH), (C(Regexp), C(String));
     OP(Freeze, FREEZE), (C(String));
+    OP(UMinus, UMINUS), (C(String));
     OP(Max, MAX), (C(Array));
     OP(Min, MIN), (C(Array));
 #undef C
diff --git a/vm_core.h b/vm_core.h
index 5b930a8aa7..437c4d9c2d 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -454,6 +454,7 @@ enum ruby_basic_operators {
     BOP_NEQ,
     BOP_MATCH,
     BOP_FREEZE,
+    BOP_UMINUS,
     BOP_MAX,
     BOP_MIN,