Avoid a hash allocation when calling def f(kw: 1) with keyword splat

c20e819 made calling a method
that accepts specific keywords but not a keyword splat with a keyword
splat allocating a hash when it previously did not.

Instead of duplicating the hash and removing hash entries,
lookup in the provided hash without duplicating the hash, and
track to make sure all hash entries in the hash were looked up
(extra hash entries would be errors).

vm_args.c

@@ -398,7 +398,7 @@ args_setup_kw_parameters(rb_execution_context_t *const ec, const rb_iseq_t *cons
 
 static void
 args_setup_kw_parameters_from_kwsplat(rb_execution_context_t *const ec, const rb_iseq_t *const iseq,
-                         VALUE keyword_hash, VALUE *const locals)
+                         VALUE keyword_hash, VALUE *const locals, bool remove_hash_value)
 {
     const ID *acceptable_keywords = ISEQ_BODY(iseq)->param.keyword->table;
     const int req_key_num = ISEQ_BODY(iseq)->param.keyword->required_num;
@@ -407,13 +407,22 @@ args_setup_kw_parameters_from_kwsplat(rb_execution_context_t *const ec, const rb
     VALUE missing = 0;
     int i, di;
     int unspecified_bits = 0;
+    size_t keyword_size = RHASH_SIZE(keyword_hash);
     VALUE unspecified_bits_value = Qnil;
 
     for (i=0; i<req_key_num; i++) {
         VALUE key = ID2SYM(acceptable_keywords[i]);
-        VALUE deleted_value = rb_hash_delete_entry(keyword_hash, key);
-        if (!UNDEF_P(deleted_value)) {
-            locals[i] = deleted_value;
+        VALUE value;
+        if (remove_hash_value) {
+            value = rb_hash_delete_entry(keyword_hash, key);
+        }
+        else {
+            value = rb_hash_lookup2(keyword_hash, key, Qundef);
+        }
+
+        if (!UNDEF_P(value)) {
+            keyword_size--;
+            locals[i] = value;
         }
         else {
             if (!missing) missing = rb_ary_hidden_new(1);
@@ -425,9 +434,17 @@ args_setup_kw_parameters_from_kwsplat(rb_execution_context_t *const ec, const rb
 
     for (di=0; i<key_num; i++, di++) {
         VALUE key = ID2SYM(acceptable_keywords[i]);
-        VALUE deleted_value = rb_hash_delete_entry(keyword_hash, key);
-        if (!UNDEF_P(deleted_value)) {
-            locals[i] = deleted_value;
+        VALUE value;
+        if (remove_hash_value) {
+            value = rb_hash_delete_entry(keyword_hash, key);
+        }
+        else {
+            value = rb_hash_lookup2(keyword_hash, key, Qundef);
+        }
+
+        if (!UNDEF_P(value)) {
+            keyword_size--;
+            locals[i] = value;
         }
         else {
             if (UNDEF_P(default_values[di])) {
@@ -462,7 +479,16 @@ args_setup_kw_parameters_from_kwsplat(rb_execution_context_t *const ec, const rb
         locals[rest_hash_index] = keyword_hash;
     }
     else {
-        if (!RHASH_EMPTY_P(keyword_hash)) {
+        if (!remove_hash_value) {
+            if (keyword_size != 0) {
+                /* Recurse with duplicated keyword hash in remove mode.
+                 * This is simpler than writing code to check which entries in the hash do not match.
+                 * This will raise an exception, so the additional performance impact shouldn't be material.
+                 */
+                args_setup_kw_parameters_from_kwsplat(ec, iseq, rb_hash_dup(keyword_hash), locals, true);
+            }
+        }
+        else if (!RHASH_EMPTY_P(keyword_hash)) {
             argument_kw_error(ec, iseq, "unknown", rb_hash_keys(keyword_hash));
         }
     }
@@ -808,8 +834,12 @@ setup_parameters_complex(rb_execution_context_t * const ec, const rb_iseq_t * co
             args_setup_kw_parameters(ec, iseq, args->kw_argv, kw_arg->keyword_len, kw_arg->keywords, klocals);
         }
         else if (!NIL_P(keyword_hash)) {
-            keyword_hash = check_kwrestarg(keyword_hash, &kw_flag);
-            args_setup_kw_parameters_from_kwsplat(ec, iseq, keyword_hash, klocals);
+            bool remove_hash_value = false;
+            if (ISEQ_BODY(iseq)->param.flags.has_kwrest) {
+                keyword_hash = check_kwrestarg(keyword_hash, &kw_flag);
+                remove_hash_value = true;
+            }
+            args_setup_kw_parameters_from_kwsplat(ec, iseq, keyword_hash, klocals, remove_hash_value);
         }
         else {
             VM_ASSERT(args_argc(args) == 0);