ZJIT: Add new test and TODO

This was supposed to go in with ruby#16476 but I didn't realize I never pushed...

Author: tekknolagi

zjit/src/hir.rs

@@ -7905,6 +7905,8 @@ pub fn iseq_to_hir(iseq: *const rb_iseq_t) -> Result<Function, ParseError> {
                         let join_block = insn_idx_to_block.get(&insn_idx).copied().unwrap_or_else(|| fun.new_block(insn_idx));
                         let join_param = fun.push_insn(join_block, Insn::Param);
                         // Dedup by expected shape so objects with different classes but the same shape can share code
+                        // TODO(max): De-duplicate further by checking ivar offsets to allow
+                        // different shapes with the same ivar layout to share code
                         let mut seen_shapes = Vec::with_capacity(summary.buckets().len());
                         for &profiled_type in summary.buckets() {
                             // End of the buckets

zjit/src/hir/opt_tests.rs

@@ -7507,6 +7507,68 @@ mod hir_opt_tests {
         ");
     }
 
+    #[test]
+    fn test_optimize_getivar_polymorphic_with_subclass() {
+        set_call_threshold(3);
+        eval(r#"
+            class C
+              def initialize
+                @foo = 3
+              end
+
+              def foo = @foo + 1
+            end
+
+            class D < C
+              def initialize
+                super
+                @bar = 4
+              end
+            end
+
+            O1 = C.new
+            O2 = D.new
+            O1.foo
+            O2.foo
+        "#);
+        assert_snapshot!(hir_string_proc("C.instance_method(:foo)"), @"
+        fn foo@<compiled>:7:
+        bb1():
+          EntryPoint interpreter
+          v1:BasicObject = LoadSelf
+          Jump bb3(v1)
+        bb2():
+          EntryPoint JIT(0)
+          v4:BasicObject = LoadArg :self@0
+          Jump bb3(v4)
+        bb3(v6:BasicObject):
+          PatchPoint SingleRactorMode
+          v11:HeapBasicObject = GuardType v6, HeapBasicObject
+          v12:CShape = LoadField v11, :_shape_id@0x1000
+          v14:CShape[0x1001] = Const CShape(0x1001)
+          v15:CBool = IsBitEqual v12, v14
+          IfTrue v15, bb5()
+          v19:CShape[0x1002] = Const CShape(0x1002)
+          v20:CBool = IsBitEqual v12, v19
+          IfTrue v20, bb6()
+          v24:BasicObject = GetIvar v11, :@foo
+          Jump bb4(v24)
+        bb5():
+          v17:BasicObject = LoadField v11, :@foo@0x1003
+          Jump bb4(v17)
+        bb6():
+          v22:BasicObject = LoadField v11, :@foo@0x1003
+          Jump bb4(v22)
+        bb4(v13:BasicObject):
+          v27:Fixnum[1] = Const Value(1)
+          PatchPoint MethodRedefined(Integer@0x1008, +@0x1010, cme:0x1018)
+          v38:Fixnum = GuardType v13, Fixnum
+          v39:Fixnum = FixnumAdd v38, v27
+          CheckInterrupts
+          Return v39
+        ");
+    }
+
     #[test]
     fn test_dont_optimize_attr_accessor_polymorphic() {
         set_call_threshold(3);