YJIT: Compile splat calls to iseqs with rest params

Test interactions with optional parameters.

bootstraptest/test_yjit.rb

@@ -1,3 +1,37 @@
+# test splat filling required and feeding rest
+assert_equal '[0, 1, 2, [3, 4]]', %q{
+  public def lead_rest(a, b, *rest)
+    [self, a, b, rest]
+  end
+
+  def call(args) = 0.lead_rest(*args)
+
+  call([1, 2, 3, 4])
+}
+
+# test missing opts are nil initialized
+assert_equal '[[0, 1, nil, 3], [0, 1, nil, 3], [0, 1, nil, 3, []], [0, 1, nil, 3, []]]', %q{
+  public def lead_opts(a, b=binding.local_variable_get(:c), c=3)
+    [self, a, b, c]
+  end
+
+  public def opts_rest(a=raise, b=binding.local_variable_get(:c), c=3, *rest)
+    [self, a, b, c, rest]
+  end
+
+  def call(args)
+    [
+      0.lead_opts(1),
+      0.lead_opts(*args),
+
+      0.opts_rest(1),
+      0.opts_rest(*args),
+    ]
+  end
+
+  call([1])
+}
+
 # test filled optionals with unspecified keyword param
 assert_equal 'ok', %q{
   def opt_rest_opt_kw(_=1, *, k: :ok) = k

yjit/src/codegen.rs

@@ -5665,7 +5665,6 @@ fn gen_send_iseq(
     exit_if_has_kwrest(asm, iseq)?;
     exit_if_splat_and_ruby2_keywords(asm, jit, flags)?;
     exit_if_has_rest_and_captured(asm, iseq_has_rest, captured_opnd)?;
-    exit_if_has_rest_and_splat(asm, iseq_has_rest, flags)?;
     exit_if_has_rest_and_supplying_kws(asm, iseq_has_rest, iseq, supplying_kws)?;
     exit_if_supplying_kw_and_has_no_kw(asm, supplying_kws, iseq)?;
     exit_if_supplying_kws_and_accept_no_kwargs(asm, supplying_kws, iseq)?;
@@ -6426,11 +6425,6 @@ fn exit_if_has_rest_and_captured(asm: &mut Assembler, iseq_has_rest: bool, captu
     exit_if(asm, iseq_has_rest && captured_opnd.is_some(), Counter::send_iseq_has_rest_and_captured)
 }
 
-#[must_use]
-fn exit_if_has_rest_and_splat( asm: &mut Assembler, iseq_has_rest: bool, flags: u32) -> Option<()> {
-    exit_if(asm, iseq_has_rest && flags & VM_CALL_ARGS_SPLAT != 0, Counter::send_iseq_has_rest_and_splat)
-}
-
 #[must_use]
 fn exit_if_has_rest_and_supplying_kws(asm: &mut Assembler, iseq_has_rest: bool, iseq: *const rb_iseq_t, supplying_kws: bool) -> Option<()> {
     exit_if(