From: Jonathan Wakely <jwakely@redhat.com>
Date: Fri, 14 Jun 2019 18:11:17 +0000 (+0100)
Subject: Optimize filesystem::path::parent_path()
X-Git-Tag: releases/gcc-9.2.0~241
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=873557820764285a4b8da2d86333c26913449740;p=thirdparty%2Fgcc.git

Optimize filesystem::path::parent_path()

Parsing a complete string is more efficient than appending each
component one-by-one.

Backport from mainline
2019-05-29  Jonathan Wakely  <jwakely@redhat.com>

	* src/c++17/fs_path.cc (path::parent_path()): Create whole path at
	once instead of building it iteratively.

From-SVN: r272303
---

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 7b46e22eca02..d4cb3be5e299 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,11 @@
+2019-06-14  Jonathan Wakely  <jwakely@redhat.com>
+
+	Backport from mainline
+	2019-05-29  Jonathan Wakely  <jwakely@redhat.com>
+
+	* src/c++17/fs_path.cc (path::parent_path()): Create whole path at
+	once instead of building it iteratively.
+
 2019-06-14  Jonathan Wakely  <jwakely@redhat.com>
 
 	Backport from mainline
diff --git a/libstdc++-v3/src/c++17/fs_path.cc b/libstdc++-v3/src/c++17/fs_path.cc
index 8e01bf510d3e..c438ddc61fd8 100644
--- a/libstdc++-v3/src/c++17/fs_path.cc
+++ b/libstdc++-v3/src/c++17/fs_path.cc
@@ -1523,11 +1523,9 @@ path::parent_path() const
     __ret = *this;
   else if (_M_cmpts.size() >= 2)
     {
-      for (auto __it = _M_cmpts.begin(), __end = std::prev(_M_cmpts.end());
-	   __it != __end; ++__it)
-	{
-	  __ret /= *__it;
-	}
+      const auto parent = std::prev(_M_cmpts.end(), 2);
+      const auto len = parent->_M_pos + parent->_M_pathname.length();
+      __ret.assign(_M_pathname.substr(0, len));
     }
   return __ret;
 }