[incfs] Optimize path::join for appending

Append path strings to the first argument if it's an rvalue

Bug: 183435580
Test: atest libincfs-test service.incremental_test
Change-Id: I52c4a1f0e4ad3547aeccac96a3393323e3be9adb

1 files changed, 15 insertions, 5 deletions

diff --git a/services/incremental/path.h b/services/incremental/path.h
index 3e5fd21b6535..e12e1d027055 100644
--- a/services/incremental/path.h
+++ b/services/incremental/path.h
@@ -89,15 +89,25 @@ std::optional<bool> isEmptyDir(std::string_view dir);
 bool startsWith(std::string_view path, std::string_view prefix);
 
 template <class... Paths>
-std::string join(std::string_view first, std::string_view second, Paths&&... paths) {
-    std::string result;
+std::string join(std::string&& first, std::string_view second, Paths&&... paths) {
+    std::string& result = first;
     {
         using std::size;
         result.reserve(first.size() + second.size() + 1 + (sizeof...(paths) + ... + size(paths)));
     }
-    result.assign(first);
-    (details::append_next_path(result, second), ..., details::append_next_path(result, paths));
-    return result;
+    (details::append_next_path(result, second), ...,
+     details::append_next_path(result, std::forward<Paths>(paths)));
+    return std::move(result);
+}
+
+template <class... Paths>
+std::string join(std::string_view first, std::string_view second, Paths&&... paths) {
+    return path::join(std::string(), first, second, std::forward<Paths>(paths)...);
+}
+
+template <class... Paths>
+std::string join(const char* first, std::string_view second, Paths&&... paths) {
+    return path::join(std::string_view(first), second, std::forward<Paths>(paths)...);
 }
 
 } // namespace android::incremental::path