fix condition and add another debug counter

mc_inline_miss_same_def is added to check same method or not.
Also the mc_inline_miss_same_cc calculation was fixed.

debug_counter.h

@@ -21,6 +21,7 @@ RB_DEBUG_COUNTER(mc_inline_miss_invalidated) // IMC miss by invalidated ME
 RB_DEBUG_COUNTER(mc_inline_miss_empty)       // IMC miss because prev is empty slot
 RB_DEBUG_COUNTER(mc_inline_miss_same_cc)     // IMC miss, but same CC
 RB_DEBUG_COUNTER(mc_inline_miss_same_cme)    // IMC miss, but same CME
+RB_DEBUG_COUNTER(mc_inline_miss_same_def)    // IMC miss, but same definition
 RB_DEBUG_COUNTER(mc_inline_miss_diff)        // IMC miss, different methods
 
 RB_DEBUG_COUNTER(mc_cme_complement)          // number of acquiring complement CME

vm_insnhelper.c

@@ -1694,12 +1694,16 @@ rb_vm_search_method_slowpath(VALUE cd_owner, struct rb_call_data *cd, VALUE klas
             // empty
             RB_DEBUG_COUNTER_INC(mc_inline_miss_empty);
         }
-        else if (old_cc == cd->cc) {
+        else if (old_cc == cc) {
             RB_DEBUG_COUNTER_INC(mc_inline_miss_same_cc);
         }
         else if (vm_cc_cme(old_cc) == vm_cc_cme(cc)) {
             RB_DEBUG_COUNTER_INC(mc_inline_miss_same_cme);
         }
+        else if (vm_cc_cme(old_cc) && vm_cc_cme(cc) &&
+                 vm_cc_cme(old_cc)->def == vm_cc_cme(cc)->def) {
+            RB_DEBUG_COUNTER_INC(mc_inline_miss_same_def);
+        }
         else {
             RB_DEBUG_COUNTER_INC(mc_inline_miss_diff);
         }