ZJIT: Profile nil? calls

This allows ZJIT to profile `nil?` calls and create type guards for
its receiver.

- Add `zjit_profile` to `opt_nil_p` insn
- Start profiling `opt_nil_p` calls
- Use `runtime_exact_ruby_class` instead of `exact_ruby_class` to determine
  the profiled receiver class

Author: st0012

insns.def

@@ -996,6 +996,7 @@ opt_nil_p
 (CALL_DATA cd)
 (VALUE recv)
 (VALUE val)
+// attr bool zjit_profile = true;
 {
     val = vm_opt_nil_p(GET_ISEQ(), cd, recv);
 

zjit/src/cruby_bindings.inc.rs

@@ -1547,7 +1547,7 @@ impl Function {
             } else {
                 let iseq_insn_idx = fun.frame_state(state).insn_idx;
                 let Some(recv_type) = fun.profiled_type_of_at(self_val, iseq_insn_idx) else { return Err(()) };
-                let Some(recv_class) = recv_type.exact_ruby_class() else { return Err(()) };
+                let Some(recv_class) = recv_type.runtime_exact_ruby_class() else { return Err(()) };
                 (recv_class, Some(recv_type.unspecialized()))
             };
 
@@ -6641,4 +6641,24 @@ mod opt_tests {
               Return v5
         "#]]);
     }
+
+    #[test]
+    fn test_guard_nil_for_nil_opt() {
+        eval("
+            def test(val)
+              val.nil?
+            end
+
+            test(nil)
+            test(nil)
+        ");
+        assert_optimized_method_hir("test", expect![[r#"
+            fn test:
+            bb0(v0:BasicObject, v1:BasicObject):
+              PatchPoint MethodRedefined(NilClass@0x1000, nil?@0x1008)
+              v7:NilClassExact = GuardType v1, NilClassExact
+              v8:TrueClassExact = CCall nil?@0x1010, v7
+              Return v8
+        "#]]);
+    }
 }

zjit/src/hir.rs

@@ -51,6 +51,7 @@ pub extern "C" fn rb_zjit_profile_insn(opcode: ruby_vminsn_type, ec: EcPtr) {
 /// Profile a YARV instruction
 fn profile_insn(profiler: &mut Profiler, opcode: ruby_vminsn_type) {
     match opcode {
+        YARVINSN_opt_nil_p => profile_operands(profiler, 1),
         YARVINSN_opt_plus  => profile_operands(profiler, 2),
         YARVINSN_opt_minus => profile_operands(profiler, 2),
         YARVINSN_opt_mult  => profile_operands(profiler, 2),