From 6c3f77255aa49b36f68c43add3864a0b7b6e84f2 Mon Sep 17 00:00:00 2001
From: Aaron Patterson <aaron.patterson@gmail.com>
Date: Thu, 3 Dec 2015 13:31:15 -0800
Subject: [PATCH] optimize case / when for `nil`

---
 compile.c              |  2 ++
 insns.def              |  1 +
 object.c               |  1 +
 test/ruby/test_case.rb | 21 +++++++++++++++++++++
 vm.c                   |  3 ++-
 vm_core.h              |  1 +
 6 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/compile.c b/compile.c
index bb8fe86..f494350 100644
--- a/compile.c
+++ b/compile.c
@@ -2893,6 +2893,8 @@ case_when_optimizable_literal(NODE * node)
 	}
 	break;
       }
+      case NODE_NIL:
+	 return Qnil;
       case NODE_STR:
 	return node->nd_lit = rb_fstring(node->nd_lit);
     }
diff --git a/insns.def b/insns.def
index 36a132b..facb77d 100644
--- a/insns.def
+++ b/insns.def
@@ -1272,6 +1272,7 @@ opt_case_dispatch
 				   SYMBOL_REDEFINED_OP_FLAG |
 				   FIXNUM_REDEFINED_OP_FLAG |
 				   BIGNUM_REDEFINED_OP_FLAG |
+				   NIL_REDEFINED_OP_FLAG    |
 				   STRING_REDEFINED_OP_FLAG)) {
 	    st_data_t val;
 	    if (st_lookup(RHASH_TBL_RAW(hash), key, &val)) {
diff --git a/object.c b/object.c
index ff2db0b..e2bcf74 100644
--- a/object.c
+++ b/object.c
@@ -3468,6 +3468,7 @@ InitVM_Object(void)
     rb_define_method(rb_cNilClass, "&", false_and, 1);
     rb_define_method(rb_cNilClass, "|", false_or, 1);
     rb_define_method(rb_cNilClass, "^", false_xor, 1);
+    rb_define_method(rb_cNilClass, "===", rb_equal, 1);
 
     rb_define_method(rb_cNilClass, "nil?", rb_true, 0);
     rb_undef_alloc_func(rb_cNilClass);
diff --git a/test/ruby/test_case.rb b/test/ruby/test_case.rb
index f20d1df..b9f8ab2 100644
--- a/test/ruby/test_case.rb
+++ b/test/ruby/test_case.rb
@@ -121,4 +121,25 @@ def test_nomethoderror
       end
     }
   end
+
+  module NilEqq
+    refine NilClass do
+      def === other
+        false
+      end
+    end
+  end
+
+  class NilEqqClass
+    using NilEqq
+
+    def eqq(a)
+      case a; when nil then nil; else :not_nil; end
+    end
+  end
+
+
+  def test_deoptimize_nil
+    assert_equal :not_nil, NilEqqClass.new.eqq(nil)
+  end
 end
diff --git a/vm.c b/vm.c
index de8be50..a87b51c 100644
--- a/vm.c
+++ b/vm.c
@@ -1373,6 +1373,7 @@ vm_redefinition_check_flag(VALUE klass)
     if (klass == rb_cSymbol) return SYMBOL_REDEFINED_OP_FLAG;
     if (klass == rb_cTime)   return TIME_REDEFINED_OP_FLAG;
     if (klass == rb_cRegexp) return REGEXP_REDEFINED_OP_FLAG;
+    if (klass == rb_cNilClass) return NIL_REDEFINED_OP_FLAG;
     return 0;
 }
 
@@ -1437,7 +1438,7 @@ vm_init_redefined_flag(void)
     OP(DIV, DIV), (C(Fixnum), C(Float));
     OP(MOD, MOD), (C(Fixnum), C(Float));
     OP(Eq, EQ), (C(Fixnum), C(Float), C(String));
-    OP(Eqq, EQQ), (C(Fixnum), C(Bignum), C(Float), C(Symbol), C(String));
+    OP(Eqq, EQQ), (C(Fixnum), C(Bignum), C(Float), C(Symbol), C(String), C(NilClass));
     OP(LT, LT), (C(Fixnum), C(Float));
     OP(LE, LE), (C(Fixnum), C(Float));
     OP(GT, GT), (C(Fixnum), C(Float));
diff --git a/vm_core.h b/vm_core.h
index 2343e11..657e82e 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -545,6 +545,7 @@ typedef struct rb_vm_struct {
 #define SYMBOL_REDEFINED_OP_FLAG (1 << 6)
 #define TIME_REDEFINED_OP_FLAG   (1 << 7)
 #define REGEXP_REDEFINED_OP_FLAG (1 << 8)
+#define NIL_REDEFINED_OP_FLAG    (1 << 9)
 
 #define BASIC_OP_UNREDEFINED_P(op, klass) (LIKELY((GET_VM()->redefined_flag[(op)]&(klass)) == 0))
 
-- 
2.2.1