ZJIT: Don't push frame for String#empty?

Author: jacob-shops

zjit/src/cruby_methods.rs

@@ -190,6 +190,7 @@ pub fn init() -> Annotations {
     annotate!(rb_mKernel, "itself", inline_kernel_itself);
     annotate!(rb_cString, "bytesize", types::Fixnum, no_gc, leaf);
     annotate!(rb_cString, "to_s", types::StringExact);
+    annotate!(rb_cString, "empty?", types::BoolExact, no_gc, leaf, elidable);
     annotate!(rb_cModule, "name", types::StringExact.union(types::NilClass), no_gc, leaf, elidable);
     annotate!(rb_cModule, "===", types::BoolExact, no_gc, leaf);
     annotate!(rb_cArray, "length", types::Fixnum, no_gc, leaf, elidable);

zjit/src/hir.rs

@@ -12994,4 +12994,32 @@ mod opt_tests {
           Return v27
         ");
     }
+
+    #[test]
+    fn test_string_empty() {
+        eval(r#"
+            def test(s)
+              s.empty?
+            end
+            test("asdf")
+        "#);
+        assert_snapshot!(hir_string("test"), @r"
+        fn test@<compiled>:3:
+        bb0():
+          EntryPoint interpreter
+          v1:BasicObject = LoadSelf
+          v2:BasicObject = GetLocal l0, SP@4
+          Jump bb2(v1, v2)
+        bb1(v5:BasicObject, v6:BasicObject):
+          EntryPoint JIT(0)
+          Jump bb2(v5, v6)
+        bb2(v8:BasicObject, v9:BasicObject):
+          PatchPoint MethodRedefined(String@0x1000, empty?@0x1008, cme:0x1010)
+          PatchPoint NoSingletonClass(String@0x1000)
+          v25:StringExact = GuardType v9, StringExact
+          v26:BoolExact = CCall empty?@0x1038, v25
+          CheckInterrupts
+          Return v26
+      ");
+  }
 }