From 09d8e06b335d7647fa5e0385980ba3f1a67a592b Mon Sep 17 00:00:00 2001
From: Aaron Patterson <tenderlove@ruby-lang.org>
Date: Mon, 26 Aug 2019 11:31:52 -0700
Subject: [PATCH] Try only updating hash value references

I'm afraid the keys to this hash are just integers, and those integers
may look like VALUE pointers when they are not.  Since we don't mark the
keys to this hash, it's probably safe to say that none of them have
moved, so we shouldn't try to update the references either.
---
 gc.c | 37 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/gc.c b/gc.c
index f7b770b4c3..4d8ced7611 100644
--- a/gc.c
+++ b/gc.c
@@ -7769,6 +7769,41 @@ hash_foreach_replace(st_data_t key, st_data_t value, st_data_t argp, int error)
     return ST_CONTINUE;
 }
 
+static int
+hash_replace_ref_value(st_data_t *key, st_data_t *value, st_data_t argp, int existing)
+{
+    rb_objspace_t *objspace = (rb_objspace_t *)argp;
+
+    if (gc_object_moved_p(objspace, (VALUE)*value)) {
+        *value = rb_gc_location((VALUE)*value);
+    }
+
+    return ST_CONTINUE;
+}
+
+static int
+hash_foreach_replace_value(st_data_t key, st_data_t value, st_data_t argp, int error)
+{
+    rb_objspace_t *objspace;
+
+    objspace = (rb_objspace_t *)argp;
+
+    if (gc_object_moved_p(objspace, (VALUE)value)) {
+        return ST_REPLACE;
+    }
+    return ST_CONTINUE;
+}
+
+static void
+gc_update_tbl_refs(rb_objspace_t * objspace, st_table *tbl)
+{
+    if (!tbl || tbl->num_entries == 0) return;
+
+    if (st_foreach_with_replace(tbl, hash_foreach_replace_value, hash_replace_ref_value, (st_data_t)objspace)) {
+        rb_raise(rb_eRuntimeError, "hash modified during iteration");
+    }
+}
+
 static void
 gc_update_table_refs(rb_objspace_t * objspace, st_table *tbl)
 {
@@ -8020,7 +8055,7 @@ gc_update_object_references(rb_objspace_t *objspace, VALUE obj)
         }
         if (!RCLASS_EXT(obj)) break;
         if (RCLASS_IV_TBL(obj)) {
-            gc_update_table_refs(objspace, RCLASS_IV_TBL(obj));
+            gc_update_tbl_refs(objspace, RCLASS_IV_TBL(obj));
         }
         update_class_ext(objspace, RCLASS_EXT(obj));
         update_const_tbl(objspace, RCLASS_CONST_TBL(obj));