From 50bc8c61368f84171842c1ead710a5bab6e603bd Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Thu, 5 Mar 2026 09:07:19 +0900
Subject: [PATCH] vm.c: replace constant cache generation counter with direct
 invalidation

Remove the per-entry generation field and per-state generation
counter. Invalidation now clears entries directly, removing one
comparison from every OP_GETCONST hot path.

Co-authored-by: Claude <noreply@anthropic.com>
---
 include/mruby.h |  7 +++++--
 src/variable.c  | 18 +++++++++++++++---
 src/vm.c        |  3 +--
 3 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/include/mruby.h b/include/mruby.h
index a6382e62f..ca879344b 100644
--- a/include/mruby.h
+++ b/include/mruby.h
@@ -256,7 +256,6 @@ mrb_static_assert_powerof2(MRB_CONST_CACHE_SIZE);
 struct mrb_const_cache_entry {
   const struct mrb_irep *irep;
   mrb_sym sym;
-  uint32_t generation;
   mrb_value value;
 };
 #endif
@@ -316,7 +315,6 @@ struct mrb_state {
 #endif
 
 #ifndef MRB_NO_CONST_CACHE
-  uint32_t const_generation;
   struct mrb_const_cache_entry const_cache[MRB_CONST_CACHE_SIZE];
 #endif
 
@@ -1307,6 +1305,11 @@ MRB_API void mrb_method_cache_clear(mrb_state *mrb);
 #else
 #define mrb_method_cache_clear(mrb) ((void)0)
 #endif
+#ifndef MRB_NO_CONST_CACHE
+void mrb_const_cache_clear(mrb_state *mrb);
+#else
+#define mrb_const_cache_clear(mrb) ((void)0)
+#endif
 
 /**
  * Check if mrb_open() failed
diff --git a/src/variable.c b/src/variable.c
index 3fe20ed36..92c56f76b 100644
--- a/src/variable.c
+++ b/src/variable.c
@@ -1423,6 +1423,18 @@ mrb_vm_const_get(mrb_state *mrb, mrb_sym sym)
  * Raises:
  *   E_TYPE_ERROR: If `mod` is not a class or module.
  */
+#ifndef MRB_NO_CONST_CACHE
+void
+mrb_const_cache_clear(mrb_state *mrb)
+{
+  struct mrb_const_cache_entry *cc = mrb->const_cache;
+
+  for (int i=0; i<MRB_CONST_CACHE_SIZE; cc++,i++) {
+    cc->irep = NULL;
+  }
+}
+#endif
+
 MRB_API void
 mrb_const_set(mrb_state *mrb, mrb_value mod, mrb_sym sym, mrb_value v)
 {
@@ -1432,7 +1444,7 @@ mrb_const_set(mrb_state *mrb, mrb_value mod, mrb_sym sym, mrb_value v)
   }
   mrb_obj_iv_set(mrb, mrb_obj_ptr(mod), sym, v);
 #ifndef MRB_NO_CONST_CACHE
-  mrb->const_generation++;
+  mrb_const_cache_clear(mrb);
 #endif
 
   if (!mrb->bootstrapping) {
@@ -1461,7 +1473,7 @@ mrb_const_remove(mrb_state *mrb, mrb_value mod, mrb_sym sym)
   mod_const_check(mrb, mod);
   mrb_iv_remove(mrb, mod, sym);
 #ifndef MRB_NO_CONST_CACHE
-  mrb->const_generation++;
+  mrb_const_cache_clear(mrb);
 #endif
 }
 
@@ -1481,7 +1493,7 @@ mrb_define_const_id(mrb_state *mrb, struct RClass *mod, mrb_sym name, mrb_value
 {
   mrb_obj_iv_set(mrb, (struct RObject*)mod, name, v);
 #ifndef MRB_NO_CONST_CACHE
-  mrb->const_generation++;
+  mrb_const_cache_clear(mrb);
 #endif
 }
 
diff --git a/src/vm.c b/src/vm.c
index 01da5ac2d..f4983d033 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -2032,7 +2032,7 @@ RETRY_TRY_BLOCK:
       mrb_sym sym = irep->syms[b];
       uint32_t h = mrb_int_hash_func(mrb, ((intptr_t)irep) ^ sym) & (MRB_CONST_CACHE_SIZE-1);
       struct mrb_const_cache_entry *cc = &mrb->const_cache[h];
-      if (cc->irep == irep && cc->sym == sym && cc->generation == mrb->const_generation) {
+      if (cc->irep == irep && cc->sym == sym) {
         regs[a] = cc->value;
         NEXT;
       }
@@ -2044,7 +2044,6 @@ RETRY_TRY_BLOCK:
 #ifndef MRB_NO_CONST_CACHE
         cc->irep = irep;
         cc->sym = sym;
-        cc->generation = mrb->const_generation;
         cc->value = v;
 #endif
       }