ZJIT: Make `hir::types::Class` not final and have it include metaclasses

Every class boots with a metaclass, and all metaclasses are subclasses
of Class, so `types::Class` has no business in `ExactBitsAndClass`.
In fact, we should never see an object whose RBasic::class is exactly
rb_cClass because classes get a metaclass on boot. So there is no
ClassExact type.

This fixes the side exits on getivar-module.rb that were introduced in
a8f3c34556bac709587ded4e0e4dad08932d5900 ("ZJIT: Add missing guard
on ivar access on T_{DATA,CLASS,MODULE}"). The `GuardType v, Class` checked
for exactly rb_cClass and never passed.

2 files changed, 8 insertions, 9 deletions

diff --git a/zjit/src/hir_type/gen_hir_type.rb b/zjit/src/hir_type/gen_hir_type.rb
index 37919425ce..aca8e574d6 100644
--- a/zjit/src/hir_type/gen_hir_type.rb
+++ b/zjit/src/hir_type/gen_hir_type.rb
@@ -89,7 +89,7 @@ def base_type name, c_name: nil
   [type, exact]
 end
 
-# Define a new type that cannot be subclassed.
+# Define a new type that has no subclasses and cannot be subclassed.
 # If c_name is given, mark the rb_cXYZ object as equivalent to this type.
 def final_type name, base: $object, c_name: nil
   if c_name
@@ -109,7 +109,9 @@ base_type "Range", c_name: "rb_cRange"
 base_type "Set", c_name: "rb_cSet"
 base_type "Regexp", c_name: "rb_cRegexp"
 module_class, _ = base_type "Module", c_name: "rb_cModule"
-class_ = final_type "Class", base: module_class, c_name: "rb_cClass"
+# Class cannot be subclassed by doing `class Sub < Class`,
+# but every metaclass is a subclass of `Class`. It's not final.
+module_class.subtype "Class"
 
 numeric, _ = base_type "Numeric", c_name: "rb_cNumeric"
 
diff --git a/zjit/src/hir_type/hir_type.inc.rs b/zjit/src/hir_type/hir_type.inc.rs
index f37cd57b31..46c45f17f3 100644
--- a/zjit/src/hir_type/hir_type.inc.rs
+++ b/zjit/src/hir_type/hir_type.inc.rs
@@ -9,7 +9,7 @@ mod bits {
   pub const BasicObjectSubclass: u64 = 1u64 << 3;
   pub const Bignum: u64 = 1u64 << 4;
   pub const BoolExact: u64 = FalseClass | TrueClass;
-  pub const BuiltinExact: u64 = ArrayExact | BasicObjectExact | Class | FalseClass | Float | HashExact | Integer | ModuleExact | NilClass | NumericExact | ObjectExact | RangeExact | RegexpExact | SetExact | StringExact | Symbol | TrueClass;
+  pub const BuiltinExact: u64 = ArrayExact | BasicObjectExact | FalseClass | Float | HashExact | Integer | ModuleExact | NilClass | NumericExact | ObjectExact | RangeExact | RegexpExact | SetExact | StringExact | Symbol | TrueClass;
   pub const CBool: u64 = 1u64 << 5;
   pub const CDouble: u64 = 1u64 << 6;
   pub const CInt: u64 = CSigned | CUnsigned;
@@ -231,7 +231,7 @@ pub mod types {
   pub const Truthy: Type = Type::from_bits(bits::Truthy);
   pub const TypedTData: Type = Type::from_bits(bits::TypedTData);
   pub const Undef: Type = Type::from_bits(bits::Undef);
-  pub const ExactBitsAndClass: [(u64, *const VALUE); 17] = [
+  pub const ExactBitsAndClass: [(u64, *const VALUE); 16] = [
     (bits::ObjectExact, &raw const crate::cruby::rb_cObject),
     (bits::BasicObjectExact, &raw const crate::cruby::rb_cBasicObject),
     (bits::StringExact, &raw const crate::cruby::rb_cString),
@@ -241,7 +241,6 @@ pub mod types {
     (bits::SetExact, &raw const crate::cruby::rb_cSet),
     (bits::RegexpExact, &raw const crate::cruby::rb_cRegexp),
     (bits::ModuleExact, &raw const crate::cruby::rb_cModule),
-    (bits::Class, &raw const crate::cruby::rb_cClass),
     (bits::NumericExact, &raw const crate::cruby::rb_cNumeric),
     (bits::Integer, &raw const crate::cruby::rb_cInteger),
     (bits::Float, &raw const crate::cruby::rb_cFloat),
@@ -250,9 +249,8 @@ pub mod types {
     (bits::TrueClass, &raw const crate::cruby::rb_cTrueClass),
     (bits::FalseClass, &raw const crate::cruby::rb_cFalseClass),
   ];
-  pub const SubclassBitsAndClass: [(u64, *const VALUE); 17] = [
+  pub const SubclassBitsAndClass: [(u64, *const VALUE); 16] = [
     (bits::ArraySubclass, &raw const crate::cruby::rb_cArray),
-    (bits::Class, &raw const crate::cruby::rb_cClass),
     (bits::FalseClass, &raw const crate::cruby::rb_cFalseClass),
     (bits::Integer, &raw const crate::cruby::rb_cInteger),
     (bits::HashSubclass, &raw const crate::cruby::rb_cHash),
@@ -269,9 +267,8 @@ pub mod types {
     (bits::ObjectSubclass, &raw const crate::cruby::rb_cObject),
     (bits::BasicObjectSubclass, &raw const crate::cruby::rb_cBasicObject),
   ];
-  pub const InexactBitsAndClass: [(u64, *const VALUE); 17] = [
+  pub const InexactBitsAndClass: [(u64, *const VALUE); 16] = [
     (bits::Array, &raw const crate::cruby::rb_cArray),
-    (bits::Class, &raw const crate::cruby::rb_cClass),
     (bits::FalseClass, &raw const crate::cruby::rb_cFalseClass),
     (bits::Integer, &raw const crate::cruby::rb_cInteger),
     (bits::Hash, &raw const crate::cruby::rb_cHash),