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, 1 insertions, 4 deletions

diff --git a/yjit_codegen.c b/yjit_codegen.c
index 4b53b737a0..aef5c0790d 100644
--- a/yjit_codegen.c
+++ b/yjit_codegen.c
@@ -4438,8 +4438,6 @@ gen_leave(jitstate_t *jit, ctx_t *ctx, codeblock_t *cb)
     return YJIT_END_BLOCK;
 }
 
-RUBY_EXTERN rb_serial_t ruby_vm_global_constant_state;
-
 static codegen_status_t
 gen_getglobal(jitstate_t *jit, ctx_t *ctx, codeblock_t *cb)
 {
@@ -4707,8 +4705,7 @@ gen_opt_getinlinecache(jitstate_t *jit, ctx_t *ctx, codeblock_t *cb)
 
     // See vm_ic_hit_p(). The same conditions are checked in yjit_constant_ic_update().
     struct iseq_inline_constant_cache_entry *ice = ic->entry;
-    if (!ice || // cache not filled
-        GET_IC_SERIAL(ice) != ruby_vm_global_constant_state /* cache out of date */) {
+    if (!ice) {
         // In these cases, leave a block that unconditionally side exits
         // for the interpreter to invalidate.
         return YJIT_CANT_COMPILE;