Set max_iv_count (used for object shapes) based on inline caches

With this change, we're storing the iv name on an inline cache on
setinstancevariable instructions. This allows us to check the inline
cache to count instance variables set in initialize and give us an
estimate of iv capacity for an object.

For the purpose of estimating the number of instance variables required
for an object, we're assuming that all initialize methods will call
`super`.

This change allows us to estimate the number of instance variables
required without disassembling instruction sequences.

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

1 files changed, 1 insertions, 0 deletions

diff --git a/mjit_c.rb b/mjit_c.rb
index e4933c3458..39ca89a0ea 100644
--- a/mjit_c.rb
+++ b/mjit_c.rb
@@ -310,6 +310,7 @@ module RubyVM::MJIT
     @iseq_inline_iv_cache_entry ||= CType::Struct.new(
       "iseq_inline_iv_cache_entry", Primitive.cexpr!("SIZEOF(struct iseq_inline_iv_cache_entry)"),
       value: [CType::Immediate.parse("uintptr_t"), Primitive.cexpr!("OFFSETOF((*((struct iseq_inline_iv_cache_entry *)NULL)), value)")],
+      iv_set_name: [self.ID, Primitive.cexpr!("OFFSETOF((*((struct iseq_inline_iv_cache_entry *)NULL)), iv_set_name)")],
     )
   end