Merged r13471, r13504 into 3.15 branch.

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index 969e9f7c752bfa74a9248ceee51892d429a6d761..09ca04706d77fd81c3f62506fc8db09a79556bea 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -1791,7 +1791,8 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_RegExpInitializeObject) {
         JSRegExp::kIgnoreCaseFieldIndex, ignoreCase, SKIP_WRITE_BARRIER);
     regexp->InObjectPropertyAtPut(
         JSRegExp::kMultilineFieldIndex, multiline, SKIP_WRITE_BARRIER);
-    regexp->ResetLastIndex();
+    regexp->InObjectPropertyAtPut(
+        JSRegExp::kLastIndexFieldIndex, Smi::FromInt(0), SKIP_WRITE_BARRIER);
     return regexp;
   }
 
@@ -2904,8 +2905,7 @@ MUST_USE_RESULT static MaybeObject* StringReplaceAtomRegExpWithString(
 
   int matches = indices.length();
   if (matches == 0) {
-    pattern_regexp->ResetLastIndex();
-    return *subject;
+    return isolate->heap()->undefined_value();
   }
 
   // Detect integer overflow.
@@ -3006,8 +3006,7 @@ MUST_USE_RESULT static MaybeObject* StringReplaceRegExpWithString(
   int32_t* current_match = global_cache.FetchNext();
   if (current_match == NULL) {
     if (global_cache.HasException()) return Failure::Exception();
-    regexp->ResetLastIndex();
-    return *subject;
+    return isolate->heap()->undefined_value();
   }
 
   // Guessing the number of parts that the final result string is built
@@ -3105,8 +3104,7 @@ MUST_USE_RESULT static MaybeObject* StringReplaceRegExpWithEmptyString(
   int32_t* current_match = global_cache.FetchNext();
   if (current_match == NULL) {
     if (global_cache.HasException()) return Failure::Exception();
-    regexp->ResetLastIndex();
-    return *subject;
+    return isolate->heap()->undefined_value();
   }
 
   int start = current_match[0];