Transition shape when object's capacity changes

This commit adds a `capacity` field to shapes, and adds shape
transitions whenever an object's capacity changes. Objects which are
allocated out of a bigger size pool will also make a transition from the
root shape to the shape with the correct capacity for their size pool
when they are allocated.

This commit will allow us to remove numiv from objects completely, and
will also mean we can guarantee that if two objects share shapes, their
IVs are in the same positions (an embedded and extended object cannot
share shapes). This will enable us to implement ivar sets in YJIT using
object shapes.

Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/test/-ext-/string/test_cstr.rb b/test/-ext-/string/test_cstr.rb
index d909781700..efc64119dc 100644
--- a/test/-ext-/string/test_cstr.rb
+++ b/test/-ext-/string/test_cstr.rb
@@ -43,7 +43,11 @@ class Test_StringCStr < Test::Unit::TestCase
   end
 
   def test_rb_str_new_frozen_embed
-    str = Bug::String.cstr_noembed("rbconfig.rb")
+    # "rbconfi" is the smallest "maximum embeddable string".  VWA adds
+    # a capacity field, which removes one pointer capacity for embedded objects,
+    # so if VWA is enabled, but there is only one size pool, then the
+    # maximum embeddable capacity on 32 bit machines is 8 bytes.
+    str = Bug::String.cstr_noembed("rbconfi")
     str = Bug::String.rb_str_new_frozen(str)
     assert_equal true, Bug::String.cstr_embedded?(str)
   end