eliminate cross-TU calls to rb_vm_empty_cc()

rb_vm_empty_cc(), rb_vm_empty_cc_for_super() and rb_vm_uncached_cc()
shouldn't be real function calls. rb_iseq_mark_and_move was calling
these as real functions in a loop.

iseq.c

@@ -433,8 +433,8 @@ rb_iseq_mark_and_move(const struct rb_gc_mark_ctx *ctx, rb_iseq_t *iseq, bool re
                 if (cds[i].ci) rb_gc_mark_and_move_ptr_ctx(ctx, &cds[i].ci);
 
                 const struct rb_callcache *cc = cds[i].cc;
-                if (!cc || cc == rb_vm_empty_cc() || cc == rb_vm_empty_cc_for_super() ||
-                    cc == rb_vm_uncached_cc()) {
+                if (!cc || cc == &rb_vm_empty_cc || cc == &rb_vm_empty_cc_for_super ||
+                    cc == &rb_vm_uncached_cc) {
                     // No need for marking, reference updating, or clearing
                     // We also want to avoid reassigning to improve CoW
                     continue;
@@ -450,7 +450,7 @@ rb_iseq_mark_and_move(const struct rb_gc_mark_ctx *ctx, rb_iseq_t *iseq, bool re
                     else {
                         // Either the CC or CME has been invalidated. Replace
                         // it with the empty CC so that it can be GC'd.
-                        cds[i].cc = rb_vm_empty_cc();
+                        cds[i].cc = &rb_vm_empty_cc;
                     }
                 }
             }

vm.c

@@ -771,7 +771,7 @@ rb_serial_t ruby_vm_constant_cache_invalidations = 0;
 rb_serial_t ruby_vm_constant_cache_misses = 0;
 rb_serial_t ruby_vm_global_cvar_state = 1;
 
-static const struct rb_callcache vm_empty_cc = {
+const struct rb_callcache rb_vm_empty_cc = {
     .flags = T_IMEMO | (imemo_callcache << FL_USHIFT) | VM_CALLCACHE_UNMARKABLE,
     .klass = Qundef,
     .cme_  = NULL,
@@ -784,7 +784,7 @@ static const struct rb_callcache vm_empty_cc = {
 /* Installed instead of a real cc at call sites of methods that opted out of
  * call caching: dispatch resolves the cme on every call rather than leaving a
  * cc behind on the receiver's class. */
-static const struct rb_callcache vm_uncached_cc = {
+const struct rb_callcache rb_vm_uncached_cc = {
     .flags = T_IMEMO | (imemo_callcache << FL_USHIFT) | VM_CALLCACHE_UNMARKABLE,
     .klass = Qundef,
     .cme_  = NULL,
@@ -794,7 +794,7 @@ static const struct rb_callcache vm_uncached_cc = {
     }
 };
 
-static const struct rb_callcache vm_empty_cc_for_super = {
+const struct rb_callcache rb_vm_empty_cc_for_super = {
     .flags = T_IMEMO | (imemo_callcache << FL_USHIFT) | VM_CALLCACHE_UNMARKABLE,
     .klass = Qundef,
     .cme_  = NULL,
@@ -5464,22 +5464,4 @@ vm_collect_usage_register(int reg, int isset)
 }
 #endif
 
-const struct rb_callcache *
-rb_vm_empty_cc(void)
-{
-    return &vm_empty_cc;
-}
-
-const struct rb_callcache *
-rb_vm_empty_cc_for_super(void)
-{
-    return &vm_empty_cc_for_super;
-}
-
-const struct rb_callcache *
-rb_vm_uncached_cc(void)
-{
-    return &vm_uncached_cc;
-}
-
 #include "vm_call_iseq_optimized.inc" /* required from vm_insnhelper.c */

vm_callinfo.h

@@ -324,11 +324,11 @@ enum vm_cc_type {
     cc_type_refinement,
 };
 
-extern const struct rb_callcache *rb_vm_empty_cc(void);
-extern const struct rb_callcache *rb_vm_empty_cc_for_super(void);
-extern const struct rb_callcache *rb_vm_uncached_cc(void);
+extern const struct rb_callcache rb_vm_empty_cc;
+extern const struct rb_callcache rb_vm_empty_cc_for_super;
+extern const struct rb_callcache rb_vm_uncached_cc;
 
-#define vm_cc_empty() rb_vm_empty_cc()
+#define vm_cc_empty() (&rb_vm_empty_cc)
 
 static inline VALUE
 cc_check_class(VALUE klass)

vm_eval.c

@@ -420,7 +420,7 @@ gccct_method_search_slowpath(rb_vm_t *vm, VALUE klass, unsigned int index, const
 
     vm_search_method_slowpath0(vm->self, &cd, klass);
 
-    if (UNLIKELY(cd.cc == rb_vm_uncached_cc())) {
+    if (UNLIKELY(cd.cc == &rb_vm_uncached_cc)) {
         // Carries no cme, so it would only ever miss here. Don't evict a usable entry for it.
         return cd.cc;
     }
@@ -571,7 +571,7 @@ rb_call0(rb_execution_context_t *ec,
 
     const struct rb_callcache *cc = gccct_method_search(ec, recv, mid, &ci);
 
-    if (UNLIKELY(cc == rb_vm_uncached_cc())) {
+    if (UNLIKELY(cc == &rb_vm_uncached_cc)) {
         return vm_call0_uncached(ec, recv, mid, argc, argv, kw_splat, scope, self);
     }
 

vm_insnhelper.c

@@ -42,10 +42,6 @@ extern int rb_method_definition_eq(const rb_method_definition_t *d1, const rb_me
 extern VALUE rb_make_no_method_exception(VALUE exc, VALUE format, VALUE obj,
                                          int argc, const VALUE *argv, int priv);
 
-static const struct rb_callcache vm_empty_cc;
-static const struct rb_callcache vm_empty_cc_for_super;
-static const struct rb_callcache vm_uncached_cc;
-
 /* control stack frame */
 
 static rb_control_frame_t *vm_get_ruby_level_caller_cfp(const rb_execution_context_t *ec, const rb_control_frame_t *cfp);
@@ -2110,8 +2106,8 @@ vm_populate_cc(VALUE klass, const struct rb_callinfo * const ci, ID mid)
 
     if (cme == NULL) {
         // undef or not found: can't cache the information
-        VM_ASSERT(vm_cc_cme(&vm_empty_cc) == NULL);
-        return &vm_empty_cc;
+        VM_ASSERT(vm_cc_cme(&rb_vm_empty_cc) == NULL);
+        return &rb_vm_empty_cc;
     }
 
     if (UNLIKELY(cme->def->uncached && !(vm_ci_flag(ci) & VM_CALL_SUPER))) {
@@ -2119,7 +2115,7 @@ vm_populate_cc(VALUE klass, const struct rb_callinfo * const ci, ID mid)
         // is usually a metaclass, so the cost would scale with the number of
         // classes. invokesuper is excluded because vm_search_super_method needs a
         // cme in the cc it gets back.
-        return &vm_uncached_cc;
+        return &rb_vm_uncached_cc;
     }
 
     VALUE cc_tbl = RCLASS_WRITABLE_CC_TBL(klass);
@@ -2259,7 +2255,7 @@ vm_search_cc(const VALUE klass, const struct rb_callinfo * const ci)
 static bool
 vm_cc_resolved_p(const struct rb_callcache *cc)
 {
-    return cc != &vm_empty_cc && cc != &vm_uncached_cc;
+    return cc != &rb_vm_empty_cc && cc != &rb_vm_uncached_cc;
 }
 #endif
 
@@ -2326,7 +2322,7 @@ vm_search_method_slowpath0(VALUE cd_owner, struct rb_call_data *cd, VALUE klass)
     }
 
 #if USE_DEBUG_COUNTER
-    const struct rb_callcache *empty_cc = &vm_empty_cc;
+    const struct rb_callcache *empty_cc = &rb_vm_empty_cc;
     if (!old_cc || old_cc == empty_cc) {
         // empty
         RB_DEBUG_COUNTER_INC(mc_inline_miss_empty);
@@ -2386,7 +2382,7 @@ vm_search_method_fastpath(const struct rb_control_frame_struct *reg_cfp, struct
     if (vm_cc_hit_p(cc, cd, klass)) {
         return cc;
     }
-    if (UNLIKELY(cc == &vm_uncached_cc)) {
+    if (UNLIKELY(cc == &rb_vm_uncached_cc)) {
         return cc;
     }
 
@@ -2435,7 +2431,7 @@ rb_zjit_vm_search_method(VALUE cd_owner, struct rb_call_data *cd, VALUE recv)
     VALUE klass = CLASS_OF(recv);
     const struct rb_callcache *cc = cd->cc;
     if (!vm_cc_hit_p(cc, cd, klass)) {
-        if (UNLIKELY(cc == &vm_uncached_cc)) {
+        if (UNLIKELY(cc == &rb_vm_uncached_cc)) {
             return rb_callable_method_entry(klass, vm_ci_mid(cd->ci));
         }
         cc = vm_search_method_slowpath0(cd_owner, cd, klass);
@@ -5234,7 +5230,7 @@ vm_super_outside(void)
 static const struct rb_callcache *
 empty_cc_for_super(void)
 {
-    return &vm_empty_cc_for_super;
+    return &rb_vm_empty_cc_for_super;
 }
 
 static const struct rb_callcache *