Introduce a specialize instruction for Array#pack

Instructions for this code:

```ruby
  # frozen_string_literal: true

[a].pack("C")
```

Before this commit:

```
== disasm: #<ISeq:<main>@test.rb:1 (1,0)-(3,13)>
0000 putself                                                          (   3)[Li]
0001 opt_send_without_block                 <calldata!mid:a, argc:0, FCALL|VCALL|ARGS_SIMPLE>
0003 newarray                               1
0005 putobject                              "C"
0007 opt_send_without_block                 <calldata!mid:pack, argc:1, ARGS_SIMPLE>
0009 leave
```

After this commit:

```
== disasm: #<ISeq:<main>@test.rb:1 (1,0)-(3,13)>
0000 putself                                                          (   3)[Li]
0001 opt_send_without_block                 <calldata!mid:a, argc:0, FCALL|VCALL|ARGS_SIMPLE>
0003 putobject                              "C"
0005 opt_newarray_send                      2, :pack
0008 leave
```

Co-authored-by: Maxime Chevalier-Boisvert <[email protected]>
Co-authored-by: Aaron Patterson <[email protected]>

3 files changed, 42 insertions, 1 deletions

diff --git a/yjit/src/codegen.rs b/yjit/src/codegen.rs
index 072d96f1b0..747fa1769d 100644
--- a/yjit/src/codegen.rs
+++ b/yjit/src/codegen.rs
@@ -4235,11 +4235,50 @@ fn gen_opt_newarray_send(
         gen_opt_newarray_max(jit, asm, _ocb)
     } else if method == ID!(hash) {
         gen_opt_newarray_hash(jit, asm, _ocb)
+    } else if method == ID!(pack) {
+        gen_opt_newarray_pack(jit, asm, _ocb)
     } else {
         None
     }
 }
 
+fn gen_opt_newarray_pack(
+    jit: &mut JITState,
+    asm: &mut Assembler,
+    _ocb: &mut OutlinedCb,
+) -> Option<CodegenStatus> {
+    // num == 4 ( for this code )
+    let num = jit.get_arg(0).as_u32();
+
+    // Save the PC and SP because we may call #pack
+    jit_prepare_non_leaf_call(jit, asm);
+
+    extern "C" {
+        fn rb_vm_opt_newarray_pack(ec: EcPtr, num: u32, elts: *const VALUE, fmt: VALUE) -> VALUE;
+    }
+
+    let values_opnd = asm.ctx.sp_opnd(-(num as i32));
+    let values_ptr = asm.lea(values_opnd);
+
+    let fmt_string = asm.ctx.sp_opnd(-1);
+
+    let val_opnd = asm.ccall(
+        rb_vm_opt_newarray_pack as *const u8,
+        vec![
+            EC,
+            (num - 1).into(),
+            values_ptr,
+            fmt_string
+        ],
+    );
+
+    asm.stack_pop(num.as_usize());
+    let stack_ret = asm.stack_push(Type::CString);
+    asm.mov(stack_ret, val_opnd);
+
+    Some(KeepCompiling)
+}
+
 fn gen_opt_newarray_hash(
     jit: &mut JITState,
     asm: &mut Assembler,
diff --git a/yjit/src/cruby.rs b/yjit/src/cruby.rs
index 68c0304b06..53586cb4f4 100644
--- a/yjit/src/cruby.rs
+++ b/yjit/src/cruby.rs
@@ -802,6 +802,7 @@ pub(crate) mod ids {
         name: min                content: b"min"
         name: max                content: b"max"
         name: hash               content: b"hash"
+        name: pack               content: b"pack"
         name: respond_to_missing content: b"respond_to_missing?"
         name: to_ary             content: b"to_ary"
         name: eq                 content: b"=="
diff --git a/yjit/src/cruby_bindings.inc.rs b/yjit/src/cruby_bindings.inc.rs
index a03c2d0f00..d53e630a4a 100644
--- a/yjit/src/cruby_bindings.inc.rs
+++ b/yjit/src/cruby_bindings.inc.rs
@@ -342,7 +342,8 @@ pub const BOP_AND: ruby_basic_operators = 28;
 pub const BOP_OR: ruby_basic_operators = 29;
 pub const BOP_CMP: ruby_basic_operators = 30;
 pub const BOP_DEFAULT: ruby_basic_operators = 31;
-pub const BOP_LAST_: ruby_basic_operators = 32;
+pub const BOP_PACK: ruby_basic_operators = 32;
+pub const BOP_LAST_: ruby_basic_operators = 33;
 pub type ruby_basic_operators = u32;
 pub type rb_serial_t = ::std::os::raw::c_ulonglong;
 pub const imemo_env: imemo_type = 0;