From 43472a30014924f77790d9d05593546d19043fb5 Mon Sep 17 00:00:00 2001
From: Shannon Skipper <shannonskipper@gmail.com>
Date: Thu, 5 Jun 2025 16:37:01 -0700
Subject: [PATCH] ZJIT: Panic unimplemented for OOB basic block args (#13533)

---
 zjit/src/codegen.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/zjit/src/codegen.rs b/zjit/src/codegen.rs
index 221f5fc3f9..dd9d41183d 100644
--- a/zjit/src/codegen.rs
+++ b/zjit/src/codegen.rs
@@ -713,6 +713,12 @@ fn gen_save_sp(asm: &mut Assembler, stack_size: usize) {
 fn param_reg(idx: usize) -> Reg {
     // To simplify the implementation, allocate a fixed register for each basic block argument for now.
     // TODO: Allow allocating arbitrary registers for basic block arguments
+    if idx >= ALLOC_REGS.len() {
+        unimplemented!(
+            "register spilling not yet implemented, too many basic block arguments ({}/{})",
+            idx + 1, ALLOC_REGS.len()
+        );
+    }
     ALLOC_REGS[idx]
 }