YJIT: Reject keywords hash in -1 arity cfunc splat support

`test_keyword.rb` caught this issue. Just need to run with `threshold=1`

bootstraptest/test_yjit.rb

@@ -4658,3 +4658,19 @@ assert_equal '[[1, 2, 3], [0, 2, 3], [1, 2, 3], [2, 2, 3], [], [], [{}]]', %q{
 
   test_cfunc_vargs_splat(Foo.new, Array, Hash.ruby2_keywords_hash({}))
 }
+
+# Class#new (arity=-1), splat, and ruby2_keywords
+assert_equal '[0, {1=>1}]', %q{
+  class KwInit
+    attr_reader :init_args
+    def initialize(x = 0, **kw)
+      @init_args = [x, kw]
+    end
+  end
+
+  def test(klass, args)
+    klass.new(*args).init_args
+  end
+
+  test(KwInit, [Hash.ruby2_keywords_hash({1 => 1})])
+}

yjit.c

@@ -903,13 +903,22 @@ rb_yjit_splat_varg_checks(VALUE *sp, VALUE splat_array, rb_control_frame_t *cfp)
     // Would we overflow if we put the contents of the array onto the stack?
     if (sp + len > (VALUE *)(cfp - 2)) return Qfalse;
 
+    // Reject keywords hash since that requires duping it sometimes
+    if (len > 0) {
+        VALUE last_hash = RARRAY_AREF(splat_array, len - 1);
+        if (RB_TYPE_P(last_hash, T_HASH) &&
+                FL_TEST_RAW(last_hash, RHASH_PASS_AS_KEYWORDS)) {
+            return Qfalse;
+        }
+    }
+
     return Qtrue;
 }
 
 // Push array elements to the stack for a C method that has a variable number
 // of parameters. Returns the number of arguments the splat array contributes.
 int
-rb_yjit_splat_varg_cfunc(VALUE *stack_splat_array, bool sole_splat)
+rb_yjit_splat_varg_cfunc(VALUE *stack_splat_array)
 {
     VALUE splat_array = *stack_splat_array;
     int len;
@@ -918,17 +927,6 @@ rb_yjit_splat_varg_cfunc(VALUE *stack_splat_array, bool sole_splat)
     RUBY_ASSERT(RB_TYPE_P(splat_array, T_ARRAY));
     len = (int)RARRAY_LEN(splat_array);
 
-    // If this is a splat call without any keyword arguments, exclude the
-    // ruby2_keywords hash if it's empty
-    if (sole_splat && len > 0) {
-        VALUE last_hash = RARRAY_AREF(splat_array, len - 1);
-        if (RB_TYPE_P(last_hash, T_HASH) &&
-                FL_TEST_RAW(last_hash, RHASH_PASS_AS_KEYWORDS) &&
-                RHASH_EMPTY_P(last_hash)) {
-            len--;
-        }
-    }
-
     // Push the contents of the array onto the stack
     MEMCPY(stack_splat_array, RARRAY_CONST_PTR(splat_array), VALUE, len);
 

yjit/src/codegen.rs

@@ -6324,9 +6324,8 @@ fn gen_send_cfunc(
     // Push a dynamic number of items from the splat array to the stack when calling a vargs method
     let dynamic_splat_size = if variable_splat {
         asm_comment!(asm, "variable length splat");
-        let just_splat = usize::from(!kw_splat && kw_arg.is_null()).into();
         let stack_splat_array = asm.lea(asm.stack_opnd(0));
-        Some(asm.ccall(rb_yjit_splat_varg_cfunc as _, vec![stack_splat_array, just_splat]))
+        Some(asm.ccall(rb_yjit_splat_varg_cfunc as _, vec![stack_splat_array]))
     } else {
         None
     };

yjit/src/cruby_bindings.inc.rs

@@ -1199,10 +1199,7 @@ extern "C" {
         splat_array: VALUE,
         cfp: *mut rb_control_frame_t,
     ) -> VALUE;
-    pub fn rb_yjit_splat_varg_cfunc(
+    pub fn rb_yjit_splat_varg_cfunc(stack_splat_array: *mut VALUE) -> ::std::os::raw::c_int;
-        stack_splat_array: *mut VALUE,
-        sole_splat: bool,
-    ) -> ::std::os::raw::c_int;
     pub fn rb_yjit_dump_iseq_loc(iseq: *const rb_iseq_t, insn_idx: u32);
     pub fn rb_yjit_iseq_inspect(iseq: *const rb_iseq_t) -> *mut ::std::os::raw::c_char;
     pub fn rb_FL_TEST(obj: VALUE, flags: VALUE) -> VALUE;