YJIT: Handle splat+rest for args pass greater than required (#7468)

For example:

```ruby
def my_func(x, y, *rest)
    p [x, y, rest]
end

my_func(1, 2, 3, *[4, 5])
```

6 files changed, 54 insertions, 8 deletions

diff --git a/array.c b/array.c
index 5e09d89322..c34895a67b 100644
--- a/array.c
+++ b/array.c
@@ -1802,6 +1802,12 @@ rb_ary_unshift_m(int argc, VALUE *argv, VALUE ary)
     return ary;
 }
 
+/* non-static for yjit */
+VALUE
+rb_yjit_rb_ary_unshift_m(int argc, VALUE *argv, VALUE ary) {
+    return rb_ary_unshift_m(argc, argv, ary);
+}
+
 VALUE
 rb_ary_unshift(VALUE ary, VALUE item)
 {
diff --git a/yjit.c b/yjit.c
index d608ad32fa..f5037e6217 100644
--- a/yjit.c
+++ b/yjit.c
@@ -848,6 +848,9 @@ rb_yarv_ary_entry_internal(VALUE ary, long offset)
 }
 
 VALUE
+rb_yjit_rb_ary_unshift_m(int argc, VALUE *argv, VALUE ary);
+
+VALUE
 rb_yarv_fix_mod_fix(VALUE recv, VALUE obj)
 {
     return rb_fix_mod_fix(recv, obj);
diff --git a/yjit/bindgen/src/main.rs b/yjit/bindgen/src/main.rs
index 481c403714..71bf1df3e8 100644
--- a/yjit/bindgen/src/main.rs
+++ b/yjit/bindgen/src/main.rs
@@ -136,6 +136,7 @@ fn main() {
         .allowlist_function("rb_ary_resurrect")
         .allowlist_function("rb_ary_clear")
         .allowlist_function("rb_ary_dup")
+        .allowlist_function("rb_yjit_rb_ary_unshift_m")
 
         // From internal/array.h
         .allowlist_function("rb_ec_ary_new_from_values")
diff --git a/yjit/src/codegen.rs b/yjit/src/codegen.rs
index 64f2d6e654..74201154e4 100644
--- a/yjit/src/codegen.rs
+++ b/yjit/src/codegen.rs
@@ -1170,7 +1170,7 @@ fn gen_newarray(
     let values_ptr = if n == 0 {
         Opnd::UImm(0)
     } else {
-        asm.comment("load pointer to array elts");
+        asm.comment("load pointer to array elements");
         let offset_magnitude = (SIZEOF_VALUE as u32) * n;
         let values_opnd = ctx.sp_opnd(-(offset_magnitude as isize));
         asm.lea(values_opnd)
@@ -5321,9 +5321,13 @@ fn gen_send_iseq(
     // foo(1, 2, *[3, 4])
     // In this case, we can just dup the splat array as the rest array.
     // No need to move things around between the array and stack.
-    if iseq_has_rest && flags & VM_CALL_ARGS_SPLAT != 0 && argc - 1 != required_num {
-        gen_counter_incr!(asm, send_iseq_has_rest_and_splat_not_equal);
-        return CantCompile;
+
+    let non_rest_arg_count = argc - 1;
+    if iseq_has_rest && flags & VM_CALL_ARGS_SPLAT != 0 && non_rest_arg_count != required_num {
+        if non_rest_arg_count < required_num {
+            gen_counter_incr!(asm, send_iseq_has_rest_and_splat_fewer);
+            return CantCompile;
+        }
     }
 
     // This struct represents the metadata about the caller-specified
@@ -5792,9 +5796,36 @@ fn gen_send_iseq(
                 rb_ary_dup as *const u8,
                 vec![array],
             );
-            let stack_ret = ctx.stack_push(Type::TArray);
-            asm.mov(stack_ret, array);
+            if non_rest_arg_count > required_num {
+                // If we have more arguments than required, we need to prepend
+                // the items from the stack onto the array.
+                let diff = (non_rest_arg_count - required_num) as u32;
+
+                // diff is >0 so no need to worry about null pointer
+                asm.comment("load pointer to array elements");
+                let offset_magnitude = SIZEOF_VALUE as u32 * diff;
+                let values_opnd = ctx.sp_opnd(-(offset_magnitude as isize));
+                let values_ptr = asm.lea(values_opnd);
 
+                asm.comment("prepend stack values to rest array");
+                let array = asm.ccall(
+                    rb_yjit_rb_ary_unshift_m as *const u8,
+                    vec![Opnd::UImm(diff as u64), values_ptr, array],
+                );
+                ctx.stack_pop(diff as usize);
+
+                // We now should have the required arguments
+                // and an array of all the rest arguments
+                argc = required_num + 1;
+                let stack_ret = ctx.stack_push(Type::TArray);
+                asm.mov(stack_ret, array);
+            } else {
+                // We exit on less than right now, this is only handling
+                // the case where they are equal
+                assert!(non_rest_arg_count == required_num);
+                let stack_ret = ctx.stack_push(Type::TArray);
+                asm.mov(stack_ret, array);
+            }
         } else {
             assert!(argc >= required_num);
             let n = (argc - required_num) as u32;
@@ -5803,7 +5834,7 @@ fn gen_send_iseq(
             let values_ptr = if n == 0 {
                 Opnd::UImm(0)
             } else {
-                asm.comment("load pointer to array elts");
+                asm.comment("load pointer to array elements");
                 let offset_magnitude = SIZEOF_VALUE as u32 * n;
                 let values_opnd = ctx.sp_opnd(-(offset_magnitude as isize));
                 asm.lea(values_opnd)
diff --git a/yjit/src/cruby_bindings.inc.rs b/yjit/src/cruby_bindings.inc.rs
index 21a6d09e84..a683c5a1e4 100644
--- a/yjit/src/cruby_bindings.inc.rs
+++ b/yjit/src/cruby_bindings.inc.rs
@@ -1297,6 +1297,11 @@ extern "C" {
     pub fn rb_yarv_str_eql_internal(str1: VALUE, str2: VALUE) -> VALUE;
     pub fn rb_str_neq_internal(str1: VALUE, str2: VALUE) -> VALUE;
     pub fn rb_yarv_ary_entry_internal(ary: VALUE, offset: ::std::os::raw::c_long) -> VALUE;
+    pub fn rb_yjit_rb_ary_unshift_m(
+        argc: ::std::os::raw::c_int,
+        argv: *mut VALUE,
+        ary: VALUE,
+    ) -> VALUE;
     pub fn rb_yarv_fix_mod_fix(recv: VALUE, obj: VALUE) -> VALUE;
     pub fn rb_yjit_dump_iseq_loc(iseq: *const rb_iseq_t, insn_idx: u32);
     pub fn rb_FL_TEST(obj: VALUE, flags: VALUE) -> VALUE;
diff --git a/yjit/src/stats.rs b/yjit/src/stats.rs
index 4a13997f74..014030bf64 100644
--- a/yjit/src/stats.rs
+++ b/yjit/src/stats.rs
@@ -253,7 +253,7 @@ make_counters! {
     send_send_getter,
     send_send_builtin,
     send_iseq_has_rest_and_captured,
-    send_iseq_has_rest_and_splat_not_equal,
+    send_iseq_has_rest_and_splat_fewer,
     send_iseq_has_rest_and_send,
     send_iseq_has_rest_and_block,
     send_iseq_has_rest_and_kw,