Introduce inline cache for invokesuper

Looks good in micro benchmark:
```
$ benchmark-driver benchmark/vm2_super.yml -v --rbenv 'before;after'
before: ruby 2.7.0dev (2019-04-03 trunk 67428) [x86_64-linux]
after: ruby 2.7.0dev (2019-04-03 trunk 67428) [x86_64-linux]
last_commit=Introduce inline cache for invokesuper
Calculating -------------------------------------
                         before       after
           vm2_super    19.265M     31.280M i/s -      6.000M times in 0.311447s 0.191813s

Comparison:
                        vm2_super
               after:  31280464.2 i/s
              before:  19264906.2 i/s - 1.62x  slower
```

No significant impact to Optcarrot:
```
$ benchmark-driver benchmark.yml --rbenv='before;after' -v --output=all --repeat-count=12
before: ruby 2.7.0dev (2019-04-03 trunk 67428) [x86_64-linux]
after: ruby 2.7.0dev (2019-04-03 trunk 67428) [x86_64-linux]
last_commit=Introduce inline cache for invokesuper
Calculating -------------------------------------
                                       before                 after
Optcarrot Lan_Master.nes    48.41126024010233     47.28027196127746 fps
                            49.49212664510990     48.75072555488074
                            49.51485564376117     49.20650895701073
                            49.58351773328487     49.24563592659139
                            49.64022392458479     49.26292753046641
                            49.92566235019630     49.44496216868009
                            50.18022198879376     49.45467429762771
                            50.33038373991723     49.52003367348857
                            50.43202877523305     49.69190055704068
                            50.61368587766504     49.79856204866324
                            50.77975014460643     50.27764769510704
                            50.89807360753746     50.35785776505005
```

A little improvement to k0kubun/railsbench?:
```
$ rbenv shell before; RUBYOPT="-v" WARMUP=1 BENCHMARK=30000 bin/bench
ruby 2.7.0dev (2019-04-03 trunk 67428) [x86_64-linux]
Warmup: 1 requests
Benchmark: 30000 requests

Request per second: 897.1 [#/s] (mean)

Percentage of the requests served within a certain time (ms)
  50%    1.01
  66%    1.02
  75%    1.03
  80%    1.04
  90%    1.08
  95%    1.23
  98%    2.10
  99%    5.52
 100%   13.26

$ rbenv shell after; RUBYOPT="-v" WARMUP=1 BENCHMARK=30000 bin/bench
ruby 2.7.0dev (2019-04-03 trunk 67428) [x86_64-linux]
last_commit=Introduce inline cache for invokesuper
Warmup: 1 requests
Benchmark: 30000 requests

Request per second: 913.0 [#/s] (mean)

Percentage of the requests served within a certain time (ms)
  50%    0.99
  66%    1.00
  75%    1.01
  80%    1.02
  90%    1.06
  95%    1.20
  98%    2.12
  99%    5.57
 100%   12.39
```

No significant impact to discourse:
```
* before
categories_admin:
  50: 54
  75: 60
  90: 70
  99: 86
home_admin:
  50: 56
  75: 65
  90: 71
  99: 122
topic_admin:
  50: 64
  75: 73
  90: 79
  99: 117
categories:
  50: 32
  75: 33
  90: 46
  99: 61
home:
  50: 34
  75: 36
  90: 48
  99: 56
topic:
  50: 40
  75: 42
  90: 55
  99: 83

* after
categories_admin:
  50: 59
  75: 66
  90: 80
  99: 149
home_admin:
  50: 54
  75: 58
  90: 70
  99: 96
topic_admin:
  50: 63
  75: 66
  90: 79
  99: 115
categories:
  50: 31
  75: 32
  90: 45
  99: 65
home:
  50: 34
  75: 35
  90: 49
  99: 58
topic:
  50: 40
  75: 42
  90: 55
  99: 78
```

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@67429 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

vm_insnhelper.c

@@ -2796,7 +2796,13 @@ vm_search_super_method(const rb_control_frame_t *reg_cfp, struct rb_call_info *c
         CC_SET_FASTPATH(cc, vm_call_method_missing, TRUE);
     }
     else {
-	/* TODO: use inline cache */
+#if OPT_INLINE_METHOD_CACHE
+        if (LIKELY(GET_GLOBAL_METHOD_STATE() == cc->method_state && RCLASS_SERIAL(klass) == cc->class_serial &&
+                   ci->mid == cc->me->def->original_id))
+            return;
+        cc->method_state = GET_GLOBAL_METHOD_STATE();
+        cc->class_serial = RCLASS_SERIAL(klass);
+#endif
 	cc->me = rb_callable_method_entry(klass, ci->mid);
         CC_SET_FASTPATH(cc, vm_call_super_method, TRUE);
     }