Internalize strings in-place

src/runtime/runtime-regexp.cc

Index: src/runtime/runtime-regexp.cc
diff --git a/src/runtime/runtime-regexp.cc b/src/runtime/runtime-regexp.cc
index 9a489ecff875464e7e6cb80dab09d3c935f2bd56..4fd2e37aa71958dd6e9612db40fe960ff00a9bf8 100644
--- a/src/runtime/runtime-regexp.cc
+++ b/src/runtime/runtime-regexp.cc
@@ -431,6 +431,9 @@ MUST_USE_RESULT static Object* StringReplaceGlobalAtomRegExpWithString(
   } else {
     result_len = static_cast<int>(result_len_64);
   }
+  if (result_len == 0) {
+    return isolate->heap()->empty_string();
+  }
 
   int subject_pos = 0;
   int result_pos = 0;