RegExpMacroAssembler::CheckStackGuardState should update input string pointer

src/x64/regexp-macro-assembler-x64.cc

Index: src/x64/regexp-macro-assembler-x64.cc
diff --git a/src/x64/regexp-macro-assembler-x64.cc b/src/x64/regexp-macro-assembler-x64.cc
index 55fabc00364491618fc1c594e59ee99566b35a5f..1e0cd6a38c0a7b607c442dcdb475a3583991b898 100644
--- a/src/x64/regexp-macro-assembler-x64.cc
+++ b/src/x64/regexp-macro-assembler-x64.cc
@@ -1248,6 +1248,11 @@ int RegExpMacroAssemblerX64::CheckStackGuardState(Address* return_address,
     frame_entry<const String*>(re_frame, kInputString) = *subject;
     frame_entry<const byte*>(re_frame, kInputStart) = new_address;
     frame_entry<const byte*>(re_frame, kInputEnd) = new_address + byte_length;
+  } else if (frame_entry<const String*>(re_frame, kInputString) != *subject) {
+    // Subject string might have been a ConsString that underwent
+    // short-circuiting during GC. That will not change start_address but
+    // will change pointer inside the subject handle.
+    frame_entry<const String*>(re_frame, kInputString) = *subject;
   }
 
   return 0;