Add defined_ivar instruction

This is a variation of the `defined` instruction, for use when we
are checking for an instance variable. Splitting this out as a
separate instruction lets us skip some checks, and it also allows
us to use an instance variable cache, letting shape analysis
speed up the operation further.

compile.c

@@ -5460,9 +5460,8 @@ defined_expr0(rb_iseq_t *iseq, LINK_ANCHOR *const ret,
 
 #define PUSH_VAL(type) (needstr == Qfalse ? Qtrue : rb_iseq_defined_string(type))
       case NODE_IVAR:
-        ADD_INSN(ret, line_node, putnil);
-        ADD_INSN3(ret, line_node, defined, INT2FIX(DEFINED_IVAR),
-                  ID2SYM(node->nd_vid), PUSH_VAL(DEFINED_IVAR));
+        ADD_INSN3(ret, line_node, defined_ivar,
+                  ID2SYM(node->nd_vid), get_ivar_ic_value(iseq,node->nd_vid), PUSH_VAL(DEFINED_IVAR));
         return;
 
       case NODE_GVAR:

insns.def

@@ -701,6 +701,20 @@ defined
     }
 }
 
+/* defined?(@foo) */
+DEFINE_INSN
+defined_ivar
+(ID id, IVC ic, VALUE pushval)
+()
+(VALUE val)
+// attr bool leaf  = false;
+{
+    val = Qnil;
+    if (vm_getivar(GET_SELF(), id, GET_ISEQ(), ic, NULL, FALSE, Qundef) != Qundef) {
+        val = pushval;
+    }
+}
+
 /* check `target' matches `pattern'.
      `flag & VM_CHECKMATCH_TYPE_MASK' describe how to check pattern.
       VM_CHECKMATCH_TYPE_WHEN: ignore target and check pattern is truthy.

vm_insnhelper.c

@@ -1143,17 +1143,17 @@ fill_ivar_cache(const rb_iseq_t *iseq, IVC ic, const struct rb_callcache *cc, in
 
 #define ATTR_INDEX_NOT_SET (attr_index_t)-1
 
-ALWAYS_INLINE(static VALUE vm_getivar(VALUE, ID, const rb_iseq_t *, IVC, const struct rb_callcache *, int));
+ALWAYS_INLINE(static VALUE vm_getivar(VALUE, ID, const rb_iseq_t *, IVC, const struct rb_callcache *, int, VALUE));
 static inline VALUE
-vm_getivar(VALUE obj, ID id, const rb_iseq_t *iseq, IVC ic, const struct rb_callcache *cc, int is_attr)
+vm_getivar(VALUE obj, ID id, const rb_iseq_t *iseq, IVC ic, const struct rb_callcache *cc, int is_attr, VALUE default_value)
 {
 #if OPT_IC_FOR_IVAR
     VALUE val = Qundef;
     shape_id_t shape_id;
     VALUE * ivar_list;
 
     if (SPECIAL_CONST_P(obj)) {
-        return Qnil;
+        return default_value;
     }
 
 #if SHAPE_IN_BASIC_FLAGS
@@ -1200,7 +1200,7 @@ vm_getivar(VALUE obj, ID id, const rb_iseq_t *iseq, IVC ic, const struct rb_call
             ivar_list = ivtbl->ivptr;
         }
         else {
-            return Qnil;
+            return default_value;
         }
     }
 
@@ -1218,7 +1218,7 @@ vm_getivar(VALUE obj, ID id, const rb_iseq_t *iseq, IVC ic, const struct rb_call
         RUBY_ASSERT(cached_id != OBJ_TOO_COMPLEX_SHAPE_ID);
 
         if (index == ATTR_INDEX_NOT_SET) {
-            return Qnil;
+            return default_value;
         }
 
         val = ivar_list[index];
@@ -1260,7 +1260,7 @@ vm_getivar(VALUE obj, ID id, const rb_iseq_t *iseq, IVC ic, const struct rb_call
 
         if (shape_id == OBJ_TOO_COMPLEX_SHAPE_ID) {
             if (!rb_id_table_lookup(ROBJECT_IV_HASH(obj), id, &val)) {
-                val = Qnil;
+                val = default_value;
             }
         }
         else {
@@ -1281,13 +1281,15 @@ vm_getivar(VALUE obj, ID id, const rb_iseq_t *iseq, IVC ic, const struct rb_call
                     vm_ic_attr_index_initialize(ic, shape_id);
                 }
 
-                val = Qnil;
+                val = default_value;
             }
         }
 
     }
 
-    RUBY_ASSERT(!UNDEF_P(val));
+    if (default_value != Qundef) {
+        RUBY_ASSERT(!UNDEF_P(val));
+    }
 
     return val;
 
@@ -1572,7 +1574,7 @@ rb_vm_setclassvariable(const rb_iseq_t *iseq, const rb_control_frame_t *cfp, ID
 static inline VALUE
 vm_getinstancevariable(const rb_iseq_t *iseq, VALUE obj, ID id, IVC ic)
 {
-    return vm_getivar(obj, id, iseq, ic, NULL, FALSE);
+    return vm_getivar(obj, id, iseq, ic, NULL, FALSE, Qnil);
 }
 
 static inline void
@@ -3459,7 +3461,7 @@ vm_call_ivar(rb_execution_context_t *ec, rb_control_frame_t *cfp, struct rb_call
     const struct rb_callcache *cc = calling->cc;
     RB_DEBUG_COUNTER_INC(ccf_ivar);
     cfp->sp -= 1;
-    VALUE ivar = vm_getivar(calling->recv, vm_cc_cme(cc)->def->body.attr.id, NULL, NULL, cc, TRUE);
+    VALUE ivar = vm_getivar(calling->recv, vm_cc_cme(cc)->def->body.attr.id, NULL, NULL, cc, TRUE, Qnil);
     return ivar;
 }