From 917c02246fbb5ccc182cdadfff5539687d88170c Mon Sep 17 00:00:00 2001
From: Daniel Colson <danieljamescolson@gmail.com>
Date: Mon, 16 Jun 2025 22:16:29 -0400
Subject: [PATCH] ZJIT: SideExit on optional args

We haven't implemented optional args yet, so `SideExit` for now.
Prior to this commit `def test(a=true) a` would compile to:

```
fn test:
bb0(v0:BasicObject, v1:BasicObject):
  v3:TrueClassExact = Const Value(true)
  Return v3
```

But that is only correct for the case where the caller does not pass in
the optional arg. We probably need a guard on the PC similar to what
YJIT has.
---
 zjit/src/hir.rs | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/zjit/src/hir.rs b/zjit/src/hir.rs
index c67f25451a9afd..6ce30102a17b9b 100644
--- a/zjit/src/hir.rs
+++ b/zjit/src/hir.rs
@@ -2127,6 +2127,13 @@ pub fn iseq_to_hir(iseq: *const rb_iseq_t) -> Result<Function, ParseError> {
             let exit_state = state.clone();
             profiles.profile_stack(&exit_state);
 
+            // TODO: Remove this and implement optional arguments
+            if unsafe { get_iseq_flags_has_opt(iseq) } {
+                let exit_id = fun.push_insn(block, Insn::Snapshot { state: exit_state });
+                fun.push_insn(block, Insn::SideExit { state: exit_id });
+                break;  // End the block
+            }
+
             // try_into() call below is unfortunate. Maybe pick i32 instead of usize for opcodes.
             let opcode: u32 = unsafe { rb_iseq_opcode_at_pc(iseq, pc) }
                 .try_into()
@@ -3476,6 +3483,18 @@ mod tests {
         "#]]);
     }
 
+    #[test]
+    fn test_cant_compile_optional_arg() {
+        eval("
+            def test(a=nil) = a
+        ");
+        assert_method_hir("test",  expect![[r#"
+            fn test:
+            bb0(v0:BasicObject, v1:BasicObject):
+              SideExit
+        "#]]);
+    }
+
     #[test]
     fn test_cant_compile_splat() {
         eval("