Slight replace-in-string optimization

* lisp/subr.el (replace-in-string): Optimize to return the
original string if nothing was replaced (bug#43598).

1 files changed, 7 insertions, 4 deletions

diff --git a/lisp/subr.el b/lisp/subr.el
index dd797021f1c..357eae0f505 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -4442,10 +4442,13 @@ Unless optional argument INPLACE is non-nil, return a new string."
         (push (substring instring start pos) result))
       (push tostring result)
       (setq start (+ pos (length fromstring))))
-    ;; Get any remaining bit.
-    (unless (= start (length instring))
-      (push (substring instring start) result))
-    (apply #'concat (nreverse result))))
+    (if (null result)
+        ;; No replacements were done, so just return the original string.
+        instring
+      ;; Get any remaining bit.
+      (unless (= start (length instring))
+        (push (substring instring start) result))
+      (apply #'concat (nreverse result)))))
 
 (defun replace-regexp-in-string (regexp rep string &optional
 					fixedcase literal subexp start)