Revert "Revert "Add a specialized instruction for .nil? calls""

This reverts commit a0980f2446c0db735b8ffeb37e241370c458a626.

Retry for macOS Mojave.

benchmark/nil_p.yml

@@ -0,0 +1,9 @@
+prelude: |
+  class Niller; def nil?; true; end; end
+  xnil, notnil = nil, Object.new
+  niller = Niller.new
+benchmark:
+  - xnil.nil?
+  - notnil.nil?
+  - niller.nil?
+loop_count: 10000000

compile.c

@@ -3255,6 +3255,7 @@ iseq_specialized_instruction(rb_iseq_t *iseq, INSN *iobj)
 		  case idLength: SP_INSN(length); return COMPILE_OK;
 		  case idSize:	 SP_INSN(size);	  return COMPILE_OK;
 		  case idEmptyP: SP_INSN(empty_p);return COMPILE_OK;
+                  case idNilP:   SP_INSN(nil_p);  return COMPILE_OK;
 		  case idSucc:	 SP_INSN(succ);	  return COMPILE_OK;
 		  case idNot:	 SP_INSN(not);	  return COMPILE_OK;
 		}

defs/id.def

@@ -3,6 +3,7 @@ firstline, predefined = __LINE__+1, %[\
   max
   min
   freeze
+  nil?
   inspect
   intern
   object_id

insns.def

@@ -808,6 +808,20 @@ opt_str_freeze
     }
 }
 
+/* optimized nil? */
+DEFINE_INSN
+opt_nil_p
+(CALL_INFO ci, CALL_CACHE cc)
+(VALUE recv)
+(VALUE val)
+{
+    val = vm_opt_nil_p(ci, cc, recv);
+
+    if (val == Qundef) {
+        CALL_SIMPLE_METHOD();
+    }
+}
+
 DEFINE_INSN
 opt_str_uminus
 (VALUE str, CALL_INFO ci, CALL_CACHE cc)

object.c

@@ -1687,7 +1687,7 @@ rb_true(VALUE obj)
  */
 
 
-static VALUE
+MJIT_FUNC_EXPORTED VALUE
 rb_false(VALUE obj)
 {
     return Qfalse;

vm.c

@@ -1656,6 +1656,7 @@ vm_init_redefined_flag(void)
     OP(Call, CALL), (C(Proc));
     OP(And, AND), (C(Integer));
     OP(Or, OR), (C(Integer));
+    OP(NilP, NIL_P), (C(NilClass));
 #undef C
 #undef OP
 }

vm_core.h

@@ -550,6 +550,7 @@ enum ruby_basic_operators {
     BOP_LENGTH,
     BOP_SIZE,
     BOP_EMPTY_P,
+    BOP_NIL_P,
     BOP_SUCC,
     BOP_GT,
     BOP_GE,

vm_insnhelper.c

@@ -4228,6 +4228,26 @@ vm_opt_empty_p(VALUE recv)
     }
 }
 
+VALUE rb_false(VALUE obj);
+
+static VALUE
+vm_opt_nil_p(CALL_INFO ci, CALL_CACHE cc, VALUE recv)
+{
+    if (recv == Qnil) {
+        if (BASIC_OP_UNREDEFINED_P(BOP_NIL_P, NIL_REDEFINED_OP_FLAG)) {
+            return Qtrue;
+        } else {
+            return Qundef;
+        }
+    } else {
+        if (vm_method_cfunc_is(ci, cc, recv, rb_false)) {
+            return Qfalse;
+        } else {
+            return Qundef;
+        }
+    }
+}
+
 static VALUE
 fix_succ(VALUE x)
 {