Finer-grained inline constant cache invalidation

Current behavior - caches depend on a global counter. All constant mutations cause caches to be invalidated.

```ruby
class A
  B = 1
end

def foo
  A::B # inline cache depends on global counter
end

foo # populate inline cache
foo # hit inline cache

C = 1 # global counter increments, all caches are invalidated

foo # misses inline cache due to `C = 1`
```

Proposed behavior - caches depend on name components. Only constant mutations with corresponding names will invalidate the cache.

```ruby
class A
  B = 1
end

def foo
  A::B # inline cache depends constants named "A" and "B"
end

foo # populate inline cache
foo # hit inline cache

C = 1 # caches that depend on the name "C" are invalidated

foo # hits inline cache because IC only depends on "A" and "B"
```

Examples of breaking the new cache:

```ruby
module C
  # Breaks `foo` cache because "A" constant is set and the cache in foo depends
  # on "A" and "B"
  class A; end
end

B = 1
```

We expect the new cache scheme to be invalidated less often because names aren't frequently reused. With the cache being invalidated less, we can rely on its stability more to keep our constant references fast and reduce the need to throw away generated code in YJIT.

1 files changed, 12 insertions, 4 deletions

diff --git a/class.c b/class.c
index 9988b080d9..d3cff5f5a9 100644
--- a/class.c
+++ b/class.c
@@ -1169,11 +1169,20 @@ module_in_super_chain(const VALUE klass, VALUE module)
     return false;
 }
 
+// For each ID key in the class constant table, we're going to clear the VM's
+// inline constant caches associated with it.
+static enum rb_id_table_iterator_result
+clear_constant_cache_i(ID id, VALUE value, void *data)
+{
+    rb_clear_constant_cache_for_id(id);
+    return ID_TABLE_CONTINUE;
+}
+
 static int
 do_include_modules_at(const VALUE klass, VALUE c, VALUE module, int search_super, bool check_cyclic)
 {
     VALUE p, iclass, origin_stack = 0;
-    int method_changed = 0, constant_changed = 0, add_subclass;
+    int method_changed = 0, add_subclass;
     long origin_len;
     VALUE klass_origin = RCLASS_ORIGIN(klass);
     VALUE original_klass = klass;
@@ -1266,13 +1275,12 @@ do_include_modules_at(const VALUE klass, VALUE c, VALUE module, int search_super
 	}
 
         tbl = RCLASS_CONST_TBL(module);
-	if (tbl && rb_id_table_size(tbl)) constant_changed = 1;
+	if (tbl && rb_id_table_size(tbl))
+        rb_id_table_foreach(tbl, clear_constant_cache_i, (void *) 0);
       skip:
 	module = RCLASS_SUPER(module);
     }
 
-    if (constant_changed) rb_clear_constant_cache();
-
     return method_changed;
 }