Implement equality for CI comparison when CC searching

When we're searching for CCs, compare the argc and flags for CI rather
than comparing pointers.  This means we don't need to store a reference
to the CI, and it also naturally "de-duplicates" CC objects.

We can observe the effect with the following code:

```ruby
require "objspace"

hash = {}

p ObjectSpace.memsize_of(Hash)

eval ("a".."zzz").map { |key|
  "hash.merge(:#{key} => 1)"
}.join("; ")

p ObjectSpace.memsize_of(Hash)
```

On master:

```
$ ruby -v test.rb
ruby 3.4.0dev (2024-04-15T16:21:41Z master d019b3baec) [arm64-darwin23]
test.rb:3: warning: assigned but unused variable - hash
3424
527736
```

On this branch:

```
$ make runruby
compiling vm.c
linking miniruby
builtin_binary.inc updated
compiling builtin.c
linking static-library libruby.3.4-static.a
ln -sf ../../rbconfig.rb .ext/arm64-darwin23/rbconfig.rb
linking ruby
ld: warning: ignoring duplicate libraries: '-ldl', '-lobjc', '-lpthread'
RUBY_ON_BUG='gdb -x ./.gdbinit -p' ./miniruby -I./lib -I. -I.ext/common  ./tool/runruby.rb --extout=.ext  -- --disable-gems  ./test.rb
2240
2368
```

Co-authored-by: John Hawthorn <[email protected]>

1 files changed, 16 insertions, 8 deletions

diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index 84ef212053..108201295b 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -2023,7 +2023,8 @@ vm_ccs_push(VALUE klass, struct rb_class_cc_entries *ccs, const struct rb_callin
     VM_ASSERT(ccs->len < ccs->capa);
 
     const int pos = ccs->len++;
-    RB_OBJ_WRITE(klass, &ccs->entries[pos].ci, ci);
+    ccs->entries[pos].argc = vm_ci_argc(ci);
+    ccs->entries[pos].flag = vm_ci_flag(ci);
     RB_OBJ_WRITE(klass, &ccs->entries[pos].cc, cc);
 
     if (RB_DEBUG_COUNTER_SETMAX(ccs_maxlen, ccs->len)) {
@@ -2038,7 +2039,9 @@ rb_vm_ccs_dump(struct rb_class_cc_entries *ccs)
 {
     ruby_debug_printf("ccs:%p (%d,%d)\n", (void *)ccs, ccs->len, ccs->capa);
     for (int i=0; i<ccs->len; i++) {
-        vm_ci_dump(ccs->entries[i].ci);
+        ruby_debug_printf("CCS CI ID:flag:%x argc:%u\n",
+                ccs->entries[i].flag,
+                ccs->entries[i].argc);
         rp(ccs->entries[i].cc);
     }
 }
@@ -2050,11 +2053,8 @@ vm_ccs_verify(struct rb_class_cc_entries *ccs, ID mid, VALUE klass)
     VM_ASSERT(ccs->len <= ccs->capa);
 
     for (int i=0; i<ccs->len; i++) {
-        const struct rb_callinfo  *ci = ccs->entries[i].ci;
         const struct rb_callcache *cc = ccs->entries[i].cc;
 
-        VM_ASSERT(vm_ci_p(ci));
-        VM_ASSERT(vm_ci_mid(ci) == mid);
         VM_ASSERT(IMEMO_TYPE_P(cc, imemo_callcache));
         VM_ASSERT(vm_cc_class_check(cc, klass));
         VM_ASSERT(vm_cc_check_cme(cc, ccs->cme));
@@ -2076,6 +2076,8 @@ vm_search_cc(const VALUE klass, const struct rb_callinfo * const ci)
     VALUE ccs_data;
 
     if (cc_tbl) {
+        // CCS data is keyed on method id, so we don't need the method id
+        // for doing comparisons in the `for` loop below.
         if (rb_id_table_lookup(cc_tbl, mid, &ccs_data)) {
             ccs = (struct rb_class_cc_entries *)ccs_data;
             const int ccs_len = ccs->len;
@@ -2088,14 +2090,20 @@ vm_search_cc(const VALUE klass, const struct rb_callinfo * const ci)
             else {
                 VM_ASSERT(vm_ccs_verify(ccs, mid, klass));
 
+                // We already know the method id is correct because we had
+                // to look up the ccs_data by method id.  All we need to
+                // compare is argc and flag
+                unsigned int argc = vm_ci_argc(ci);
+                unsigned int flag = vm_ci_flag(ci);
+
                 for (int i=0; i<ccs_len; i++) {
-                    const struct rb_callinfo  *ccs_ci = ccs->entries[i].ci;
+                    unsigned int ccs_ci_argc = ccs->entries[i].argc;
+                    unsigned int ccs_ci_flag = ccs->entries[i].flag;
                     const struct rb_callcache *ccs_cc = ccs->entries[i].cc;
 
-                    VM_ASSERT(vm_ci_p(ccs_ci));
                     VM_ASSERT(IMEMO_TYPE_P(ccs_cc, imemo_callcache));
 
-                    if (ccs_ci == ci) { // TODO: equality
+                    if (ccs_ci_argc == argc && ccs_ci_flag == flag) {
                         RB_DEBUG_COUNTER_INC(cc_found_in_ccs);
 
                         VM_ASSERT(vm_cc_cme(ccs_cc)->called_id == mid);