From e54c0be60f5aa32ce06f4366a3c55db45c41093c Mon Sep 17 00:00:00 2001
From: Yi-Yo Chiang <yochiang@google.com>
Date: Wed, 2 Aug 2023 15:18:35 +0800
Subject: [PATCH] libfstab: Optimize out C++ object copy

* Edit / truncate string objects in-place, don't copy a temporary string
  object just for storing intermeidate results.
* Replace copy construct semantics with move semantics.
* Use range-based std::vector::insert() to move whole range.

Bug: 293695109
Test: CtsFsMgrTestCases
Change-Id: I5437303ba9900dbad3276a981413cba138f17157
---
 fs_mgr/libfstab/boot_config.cpp | 10 +++++-----
 fs_mgr/libfstab/fstab.cpp       |  8 ++++----
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/fs_mgr/libfstab/boot_config.cpp b/fs_mgr/libfstab/boot_config.cpp
index ae537b5d2..b21495ecd 100644
--- a/fs_mgr/libfstab/boot_config.cpp
+++ b/fs_mgr/libfstab/boot_config.cpp
@@ -122,10 +122,8 @@ void ImportKernelCmdlineFromString(const std::string& cmdline,
             if ((found = cmdline.find(quote, found + 1)) == cmdline.npos) break;
             ++found;
         }
-        std::string piece;
-        auto source = cmdline.substr(base, found - base);
-        std::remove_copy(source.begin(), source.end(),
-                         std::back_insert_iterator<std::string>(piece), quote);
+        std::string piece = cmdline.substr(base, found - base);
+        piece.erase(std::remove(piece.begin(), piece.end(), quote), piece.end());
         auto equal_sign = piece.find('=');
         if (equal_sign == piece.npos) {
             if (!piece.empty()) {
@@ -133,7 +131,9 @@ void ImportKernelCmdlineFromString(const std::string& cmdline,
                 fn(std::move(piece), "");
             }
         } else {
-            fn(piece.substr(0, equal_sign), piece.substr(equal_sign + 1));
+            std::string value = piece.substr(equal_sign + 1);
+            piece.resize(equal_sign);
+            fn(std::move(piece), std::move(value));
         }
         if (found == cmdline.npos) break;
         base = found + 1;
diff --git a/fs_mgr/libfstab/fstab.cpp b/fs_mgr/libfstab/fstab.cpp
index 21b002434..32460b17b 100644
--- a/fs_mgr/libfstab/fstab.cpp
+++ b/fs_mgr/libfstab/fstab.cpp
@@ -831,9 +831,8 @@ bool ReadDefaultFstab(Fstab* fstab) {
     Fstab default_fstab;
     const std::string default_fstab_path = GetFstabPath();
     if (!default_fstab_path.empty() && ReadFstabFromFile(default_fstab_path, &default_fstab)) {
-        for (auto&& entry : default_fstab) {
-            fstab->emplace_back(std::move(entry));
-        }
+        fstab->insert(fstab->end(), std::make_move_iterator(default_fstab.begin()),
+                      std::make_move_iterator(default_fstab.end()));
     } else {
         LINFO << __FUNCTION__ << "(): failed to find device default fstab";
     }
@@ -879,7 +878,8 @@ std::set<std::string> GetBootDevices() {
     const std::string dt_file_name = GetAndroidDtDir() + "boot_devices";
     if (GetKernelCmdline("androidboot.boot_devices", &value) || ReadDtFile(dt_file_name, &value)) {
         auto boot_devices_list = Split(value, ",");
-        return {boot_devices_list.begin(), boot_devices_list.end()};
+        return {std::make_move_iterator(boot_devices_list.begin()),
+                std::make_move_iterator(boot_devices_list.end())};
     }
 
     ImportKernelCmdline([&](std::string key, std::string value) {