diff --git a/compile.c b/compile.c
index 3f894cbe69..826260d182 100644
--- a/compile.c
+++ b/compile.c
@@ -3820,6 +3820,24 @@ iseq_peephole_optimize(rb_iseq_t *iseq, LINK_ELEMENT *list, const int do_tailcal
             }
             ELEM_REMOVE(&iobj->link);
         }
+        if (IS_NEXT_INSN_ID(&iobj->link, toregexp)) {
+            INSN *next = (INSN *)iobj->link.next;
+            if (OPERAND_AT(next, 1) == INT2FIX(1)) {
+                VALUE src = OPERAND_AT(iobj, 0);
+                int opt = (int)FIX2LONG(OPERAND_AT(next, 0));
+                VALUE path = rb_iseq_path(iseq);
+                int line = iobj->insn_info.line_no;
+                VALUE errinfo = rb_errinfo();
+                VALUE re = rb_reg_compile(src, opt, RSTRING_PTR(path), line);
+                if (NIL_P(re)) {
+                    VALUE message = rb_attr_get(rb_errinfo(), idMesg);
+                    rb_set_errinfo(errinfo);
+                    COMPILE_ERROR(iseq, line, "%" PRIsVALUE, message);
+                }
+                RB_OBJ_WRITE(iseq, &OPERAND_AT(iobj, 0), re);
+                ELEM_REMOVE(iobj->link.next);
+            }
+        }
     }
 
     if (IS_INSN_ID(iobj, concatstrings)) {
@@ -4502,47 +4520,91 @@ all_string_result_p(const NODE *node)
     }
 }
 
-static int
-compile_dstr_fragments(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const node, int *cntp)
-{
-    const struct RNode_LIST *list = RNODE_DSTR(node)->nd_next;
-    VALUE lit = rb_node_dstr_string_val(node);
-    LINK_ELEMENT *first_lit = 0;
-    int cnt = 0;
+struct dstr_ctxt {
+    rb_iseq_t *const iseq;
+    LINK_ANCHOR *const ret;
+    VALUE lit;
+    const NODE *lit_node;
+    int cnt;
+    int dregx;
+};
 
-    debugp_param("nd_lit", lit);
-    if (!NIL_P(lit)) {
-        cnt++;
-        if (!RB_TYPE_P(lit, T_STRING)) {
-            COMPILE_ERROR(ERROR_ARGS "dstr: must be string: %s",
-                          rb_builtin_type_name(TYPE(lit)));
+static int
+append_dstr_fragment(struct dstr_ctxt *args, const NODE *const node, rb_parser_string_t *str)
+{
+    VALUE s = rb_str_new_mutable_parser_string(str);
+    if (args->dregx) {
+        VALUE error = rb_reg_check_preprocess(s);
+        if (!NIL_P(error)) {
+            COMPILE_ERROR(args->iseq, nd_line(node), "%" PRIsVALUE, error);
             return COMPILE_NG;
         }
+    }
+    if (NIL_P(args->lit)) {
+        args->lit = s;
+        args->lit_node = node;
+    }
+    else {
+        rb_str_buf_append(args->lit, s);
+    }
+    return COMPILE_OK;
+}
+
+static void
+flush_dstr_fragment(struct dstr_ctxt *args)
+{
+    if (!NIL_P(args->lit)) {
+        rb_iseq_t *iseq = args->iseq;
+        VALUE lit = args->lit;
+        args->lit = Qnil;
         lit = rb_fstring(lit);
-        ADD_INSN1(ret, node, putobject, lit);
-        RB_OBJ_WRITTEN(iseq, Qundef, lit);
-        if (RSTRING_LEN(lit) == 0) first_lit = LAST_ELEMENT(ret);
+        ADD_INSN1(args->ret, args->lit_node, putobject, lit);
+        RB_OBJ_WRITTEN(args->iseq, Qundef, lit);
+        args->cnt++;
+    }
+}
+
+static int
+compile_dstr_fragments_0(struct dstr_ctxt *args, const NODE *const node)
+{
+    const struct RNode_LIST *list = RNODE_DSTR(node)->nd_next;
+    rb_parser_string_t *str = RNODE_DSTR(node)->string;
+
+    if (str) {
+        CHECK(append_dstr_fragment(args, node, str));
     }
 
     while (list) {
         const NODE *const head = list->nd_head;
         if (nd_type_p(head, NODE_STR)) {
-            lit = rb_node_str_string_val(head);
-            ADD_INSN1(ret, head, putobject, lit);
-            RB_OBJ_WRITTEN(iseq, Qundef, lit);
-            lit = Qnil;
+            CHECK(append_dstr_fragment(args, node, RNODE_STR(head)->string));
+        }
+        else if (nd_type_p(head, NODE_DSTR)) {
+            CHECK(compile_dstr_fragments_0(args, head));
         }
         else {
-            CHECK(COMPILE(ret, "each string", head));
+            flush_dstr_fragment(args);
+            rb_iseq_t *iseq = args->iseq;
+            CHECK(COMPILE(args->ret, "each string", head));
+            args->cnt++;
         }
-        cnt++;
         list = (struct RNode_LIST *)list->nd_next;
     }
-    if (NIL_P(lit) && first_lit) {
-        ELEM_REMOVE(first_lit);
-        --cnt;
-    }
-    *cntp = cnt;
+    return COMPILE_OK;
+}
+
+static int
+compile_dstr_fragments(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const node, int *cntp, int dregx)
+{
+    struct dstr_ctxt args = {
+        .iseq = iseq, .ret = ret,
+        .lit = Qnil, .lit_node = NULL,
+        .cnt = 0, .dregx = dregx,
+    };
+    CHECK(compile_dstr_fragments_0(&args, node));
+    flush_dstr_fragment(&args);
+
+    *cntp = args.cnt;
 
     return COMPILE_OK;
 }
@@ -4571,7 +4633,7 @@ compile_dstr(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const node)
         RB_OBJ_WRITTEN(iseq, Qundef, lit);
     }
     else {
-        CHECK(compile_dstr_fragments(iseq, ret, node, &cnt));
+        CHECK(compile_dstr_fragments(iseq, ret, node, &cnt, FALSE));
         ADD_INSN1(ret, node, concatstrings, INT2FIX(cnt));
     }
     return COMPILE_OK;
@@ -4593,7 +4655,7 @@ compile_dregx(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const node, i
         return COMPILE_OK;
     }
 
-    CHECK(compile_dstr_fragments(iseq, ret, node, &cnt));
+    CHECK(compile_dstr_fragments(iseq, ret, node, &cnt, TRUE));
     ADD_INSN2(ret, node, toregexp, INT2FIX(cflag), INT2FIX(cnt));
 
     if (popped) {
diff --git a/parse.y b/parse.y
index 12fac7d50e..c8629c779b 100644
--- a/parse.y
+++ b/parse.y
@@ -1480,9 +1480,6 @@ static rb_ast_id_table_t *local_tbl(struct parser_params*);
 
 static VALUE reg_compile(struct parser_params*, rb_parser_string_t*, int);
 static void reg_fragment_setenc(struct parser_params*, rb_parser_string_t*, int);
-int rb_parser_reg_fragment_check(struct parser_params*, rb_parser_string_t*, int, rb_parser_reg_fragment_error_func);
-static void reg_fragment_error(struct parser_params *, VALUE);
-#define reg_fragment_check(p, str, option) rb_parser_reg_fragment_check(p, str, option, reg_fragment_error)
 
 static int literal_concat0(struct parser_params *p, rb_parser_string_t *head, rb_parser_string_t *tail);
 static NODE *heredoc_dedent(struct parser_params*,NODE*);
@@ -13161,12 +13158,26 @@ symbol_append(struct parser_params *p, NODE *symbols, NODE *symbol)
     return list_append(p, symbols, symbol);
 }
 
+static void
+dregex_fragment_setenc(struct parser_params *p, rb_node_dregx_t *const dreg, int options)
+{
+    if (dreg->string) {
+        reg_fragment_setenc(p, dreg->string, options);
+    }
+    for (struct RNode_LIST *list = dreg->nd_next; list; list = RNODE_LIST(list->nd_next)) {
+        NODE *frag = list->nd_head;
+        if (nd_type_p(frag, NODE_STR)) {
+            reg_fragment_setenc(p, RNODE_STR(frag)->string, options);
+        }
+        else if (nd_type_p(frag, NODE_DSTR)) {
+            dregex_fragment_setenc(p, RNODE_DSTR(frag), options);
+        }
+    }
+}
+
 static NODE *
 new_regexp(struct parser_params *p, NODE *node, int options, const YYLTYPE *loc)
 {
-    struct RNode_LIST *list;
-    NODE *prev;
-
     if (!node) {
         /* Check string is valid regex */
         rb_parser_string_t *str = STRING_NEW0();
@@ -13190,37 +13201,8 @@ new_regexp(struct parser_params *p, NODE *node, int options, const YYLTYPE *loc)
         nd_set_loc(node, loc);
         rb_node_dregx_t *const dreg = RNODE_DREGX(node);
         dreg->as.nd_cflag = options & RE_OPTION_MASK;
-        if (!dreg->nd_next) {
-            /* Check string is valid regex */
-            reg_compile(p, dreg->string, options);
-        }
-        else if (dreg->string) {
-            reg_fragment_check(p, dreg->string, options);
-        }
-        prev = node;
-        for (list = dreg->nd_next; list; list = RNODE_LIST(list->nd_next)) {
-            NODE *frag = list->nd_head;
-            enum node_type type = nd_type(frag);
-            if (type == NODE_STR || (type == NODE_DSTR && !RNODE_DSTR(frag)->nd_next)) {
-                rb_parser_string_t *tail = RNODE_STR(frag)->string;
-                if (reg_fragment_check(p, tail, options) && prev && RNODE_DREGX(prev)->string) {
-                    rb_parser_string_t *lit = prev == node ? dreg->string : RNODE_STR(RNODE_LIST(prev)->nd_head)->string;
-                    if (!literal_concat0(p, lit, tail)) {
-                        return NEW_NIL(loc); /* dummy node on error */
-                    }
-                    rb_parser_str_resize(p, tail, 0);
-                    RNODE_LIST(prev)->nd_next = list->nd_next;
-                    rb_discard_node(p, list->nd_head);
-                    rb_discard_node(p, (NODE *)list);
-                    list = RNODE_LIST(prev);
-                }
-                else {
-                    prev = (NODE *)list;
-                }
-            }
-            else {
-                prev = 0;
-            }
+        if (dreg->nd_next) {
+            dregex_fragment_setenc(p, dreg, options);
         }
         if (options & RE_OPTION_ONCE) {
             node = NEW_ONCE(node, loc);
@@ -15363,13 +15345,7 @@ rb_reg_fragment_setenc(struct parser_params* p, rb_parser_string_t *str, int opt
         rb_parser_enc_associate(p, str, rb_ascii8bit_encoding());
     }
     else if (rb_is_usascii_enc(p->enc)) {
-        if (!rb_parser_is_ascii_string(p, str)) {
-            /* raise in re.c */
-            rb_parser_enc_associate(p, str, rb_usascii_encoding());
-        }
-        else {
-            rb_parser_enc_associate(p, str, rb_ascii8bit_encoding());
-        }
+        rb_parser_enc_associate(p, str, rb_ascii8bit_encoding());
     }
     return 0;
 
@@ -15385,30 +15361,6 @@ reg_fragment_setenc(struct parser_params* p, rb_parser_string_t *str, int option
     if (c) reg_fragment_enc_error(p, str, c);
 }
 
-static void
-reg_fragment_error(struct parser_params* p, VALUE err)
-{
-    compile_error(p, "%"PRIsVALUE, err);
-}
-
-#ifndef RIPPER
-int
-rb_parser_reg_fragment_check(struct parser_params* p, rb_parser_string_t *str, int options, rb_parser_reg_fragment_error_func error)
-{
-    VALUE err, str2;
-    reg_fragment_setenc(p, str, options);
-    /* TODO */
-    str2 = rb_str_new_parser_string(str);
-    err = rb_reg_check_preprocess(str2);
-    if (err != Qnil) {
-        err = rb_obj_as_string(err);
-        error(p, err);
-        return 0;
-    }
-    return 1;
-}
-#endif
-
 #ifndef UNIVERSAL_PARSER
 typedef struct {
     struct parser_params* parser;
@@ -15507,7 +15459,7 @@ reg_compile(struct parser_params* p, rb_parser_string_t *str, int options)
     if (NIL_P(re)) {
         VALUE m = rb_attr_get(rb_errinfo(), idMesg);
         rb_set_errinfo(err);
-        reg_fragment_error(p, m);
+        compile_error(p, "%"PRIsVALUE, m);
         return Qnil;
     }
     return re;
diff --git a/test/.excludes-parsey/TestM17N.rb b/test/.excludes-parsey/TestM17N.rb
deleted file mode 100644
index 7f8c44d02a..0000000000
--- a/test/.excludes-parsey/TestM17N.rb
+++ /dev/null
@@ -1 +0,0 @@
-exclude(:test_regexp_usascii, "https://bugs.ruby-lang.org/issues/20504")
diff --git a/test/.excludes-parsey/TestMixedUnicodeEscape.rb b/test/.excludes-parsey/TestMixedUnicodeEscape.rb
deleted file mode 100644
index 7bf964ebf1..0000000000
--- a/test/.excludes-parsey/TestMixedUnicodeEscape.rb
+++ /dev/null
@@ -1 +0,0 @@
-exclude(:test_basic, "https://bugs.ruby-lang.org/issues/20504")
diff --git a/test/.excludes-parsey/TestRubyLiteral.rb b/test/.excludes-parsey/TestRubyLiteral.rb
deleted file mode 100644
index 853f23a3b9..0000000000
--- a/test/.excludes-parsey/TestRubyLiteral.rb
+++ /dev/null
@@ -1 +0,0 @@
-exclude(:test_dregexp, "https://bugs.ruby-lang.org/issues/20504")
diff --git a/test/ripper/test_ripper.rb b/test/ripper/test_ripper.rb
index 5ca79e136f..070023b536 100644
--- a/test/ripper/test_ripper.rb
+++ b/test/ripper/test_ripper.rb
@@ -164,7 +164,6 @@ end
     assert_equal([[1, 8], :on_tstring_end, "\"", state(:EXPR_END)], lex.shift)
     assert_equal([[1, 9], :on_embexpr_end, "}", state(:EXPR_END)], lex.shift)
     assert_equal([[1, 10], :on_regexp_end, "/", state(:EXPR_BEG)], lex.shift)
-    assert_equal([[1, 11], :compile_error, "", state(:EXPR_END), "invalid multibyte character: /\\xCD/"], lex.shift)
     assert_empty(lex)
   end