TestGCCompact: Fix test failure when LTO enabled

https://bugs.ruby-lang.org/issues/19248
ruby/ruby@273dca3
ruby/ruby@08ae7f6

Author: sorah

debian/patches/Fix-undefined-behavior-in-shape.c.patch

@@ -0,0 +1,49 @@
+From: Peter Zhu <[email protected]>
+Date: Thu, 5 Jan 2023 08:48:19 -0500
+Subject: Fix undefined behavior in shape.c
+
+Under strict aliasing, writing to the memory location of a different
+type is not allowed and will result in undefined behavior. This was
+happening in shape.c due to `rb_id_table_lookup` writing to the memory
+location of `VALUE *` that was casted from a `rb_shape_t **`.
+
+This was causing test failures when compiled with LTO.
+
+Fixes [Bug #19248]
+
+Co-Authored-By: Alan Wu <[email protected]>
+---
+ shape.c | 13 +++++++++++--
+ 1 file changed, 11 insertions(+), 2 deletions(-)
+
+diff --git a/shape.c b/shape.c
+index 7580003..f315012 100644
+--- a/shape.c
++++ b/shape.c
+@@ -150,7 +150,11 @@ get_next_shape_internal(rb_shape_t * shape, ID id, enum shape_type shape_type, b
+ 
+             // Lookup the shape in edges - if there's already an edge and a corresponding shape for it,
+             // we can return that. Otherwise, we'll need to get a new shape
+-            if (!rb_id_table_lookup(shape->edges, id, (VALUE *)&res)) {
++            VALUE lookup_result;
++            if (rb_id_table_lookup(shape->edges, id, &lookup_result)) {
++                res = (rb_shape_t *)lookup_result;
++            }
++            else {
+                 *variation_created = had_edges;
+ 
+                 rb_shape_t * new_shape = rb_shape_alloc(id, shape);
+@@ -462,7 +466,12 @@ rb_shape_traverse_from_new_root(rb_shape_t *initial_shape, rb_shape_t *dest_shap
+         if (!next_shape->edges) {
+             return NULL;
+         }
+-        if (!rb_id_table_lookup(next_shape->edges, dest_shape->edge_name, (VALUE *)&next_shape)) {
++
++        VALUE lookup_result;
++        if (rb_id_table_lookup(next_shape->edges, dest_shape->edge_name, &lookup_result)) {
++            next_shape = (rb_shape_t *)lookup_result;
++        }
++        else {
+             return NULL;
+         }
+         break;

debian/patches/series

@@ -8,3 +8,4 @@ TestProcess-disable-gems-to-disable-rubygems_integration.patch
 ruby_default_arch.m4-don-t-require-arhitectures-to-be-kno.patch
 extract-gems-sequential-Keep-using-RUNRUBY.patch
 test_dumb_terminal-ruby-command-is-not-always-available.patch
+Fix-undefined-behavior-in-shape.c.patch