PR libstdc++/90634 reduce allocations in filesystem::path construction

	PR libstdc++/90634
	* include/experimental/bits/fs_path.h (path::path(path&&)): Only call
	_M_split_cmpts() for a path with multiple components.
	(path::_S_is_dir_sep()): Add missing 'static' keyword to function.
	* src/filesystem/path.cc (path::_M_split_cmpts()): Count number of
	components and reserve space in vector. Return early when there is
	only one component.
	* testsuite/27_io/filesystem/path/construct/90634.cc: New test.
	* testsuite/experimental/filesystem/path/construct/90634.cc: New test.

From-SVN: r271717

5 files changed, 215 insertions, 4 deletions

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 60a504b..31f7766 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,5 +1,15 @@
 2019-05-28  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/90634
+	* include/experimental/bits/fs_path.h (path::path(path&&)): Only call
+	_M_split_cmpts() for a path with multiple components.
+	(path::_S_is_dir_sep()): Add missing 'static' keyword to function.
+	* src/filesystem/path.cc (path::_M_split_cmpts()): Count number of
+	components and reserve space in vector. Return early when there is
+	only one component.
+	* testsuite/27_io/filesystem/path/construct/90634.cc: New test.
+	* testsuite/experimental/filesystem/path/construct/90634.cc: New test.
+
 	* testsuite/util/testsuite_fs.h (compare_paths): Use three-argument
 	form of std::equals for C++11 compatibility.
 
diff --git a/libstdc++-v3/include/experimental/bits/fs_path.h b/libstdc++-v3/include/experimental/bits/fs_path.h
index 588f068..9a68a27 100644
--- a/libstdc++-v3/include/experimental/bits/fs_path.h
+++ b/libstdc++-v3/include/experimental/bits/fs_path.h
@@ -195,7 +195,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     path(path&& __p) noexcept
     : _M_pathname(std::move(__p._M_pathname)), _M_type(__p._M_type)
     {
-      _M_split_cmpts();
+      if (_M_type == _Type::_Multi)
+	_M_split_cmpts();
       __p.clear();
     }
 
@@ -490,7 +491,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 	return _S_convert_loc(__s.data(), __s.data() + __s.size(), __loc);
       }
 
-    bool _S_is_dir_sep(value_type __ch)
+    static bool _S_is_dir_sep(value_type __ch)
     {
 #ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
       return __ch == L'/' || __ch == preferred_separator;
diff --git a/libstdc++-v3/src/filesystem/path.cc b/libstdc++-v3/src/filesystem/path.cc
index 92def10..dfc3bd5 100644
--- a/libstdc++-v3/src/filesystem/path.cc
+++ b/libstdc++-v3/src/filesystem/path.cc
@@ -340,6 +340,28 @@ path::_M_split_cmpts()
   if (_M_pathname.empty())
     return;
 
+  {
+    // Approximate count of components, to reserve space in _M_cmpts vector:
+    int count = 1;
+    bool saw_sep_last = _S_is_dir_sep(_M_pathname[0]);
+    bool saw_non_sep = !saw_sep_last;
+    for (value_type c : _M_pathname)
+      {
+       if (_S_is_dir_sep(c))
+         saw_sep_last = true;
+       else if (saw_sep_last)
+         {
+           ++count;
+           saw_sep_last = false;
+           saw_non_sep = true;
+         }
+      }
+    if (saw_non_sep && saw_sep_last)
+      ++count; // empty filename after trailing slash
+    if (count > 1)
+      _M_cmpts.reserve(count);
+  }
+
   size_t pos = 0;
   const size_t len = _M_pathname.size();
 
@@ -362,9 +384,13 @@ path::_M_split_cmpts()
 	      pos = 3;
 	      while (pos < len && !_S_is_dir_sep(_M_pathname[pos]))
 		++pos;
+	      if (pos == len)
+		{
+		  _M_type = _Type::_Root_name;
+		  return;
+		}
 	      _M_add_root_name(pos);
-	      if (pos < len) // also got root directory
-		_M_add_root_dir(pos);
+	      _M_add_root_dir(pos);
 	    }
 	  else
 	    {
@@ -373,6 +399,11 @@ path::_M_split_cmpts()
 	      _M_add_root_dir(0);
 	    }
 	}
+      else if (len == 1) // got root directory only
+	{
+	  _M_type = _Type::_Root_dir;
+	  return;
+	}
       else // got root directory
 	_M_add_root_dir(0);
       ++pos;
@@ -381,12 +412,28 @@ path::_M_split_cmpts()
   else if (len > 1 && _M_pathname[1] == L':')
     {
       // got disk designator
+      if (len == 2)
+	{
+	  _M_type = _Type::_Root_name;
+	  return;
+	}
       _M_add_root_name(2);
       if (len > 2 && _S_is_dir_sep(_M_pathname[2]))
 	_M_add_root_dir(2);
       pos = 2;
     }
 #endif
+  else
+    {
+      size_t n = 1;
+      for (; n < _M_pathname.size() && !_S_is_dir_sep(_M_pathname[n]); ++n)
+	{ }
+      if (n == _M_pathname.size())
+	{
+	  _M_type = _Type::_Filename;
+	  return;
+	}
+    }
 
   size_t back = pos;
   while (pos < len)
diff --git a/libstdc++-v3/testsuite/27_io/filesystem/path/construct/90634.cc b/libstdc++-v3/testsuite/27_io/filesystem/path/construct/90634.cc
new file mode 100644
index 0000000..03ec2b1
--- /dev/null
+++ b/libstdc++-v3/testsuite/27_io/filesystem/path/construct/90634.cc
@@ -0,0 +1,78 @@
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++17" }
+// { dg-do run { target c++17 } }
+
+#include <filesystem>
+#include <cstdlib>
+#include <testsuite_hooks.h>
+
+std::size_t bytes_allocated = 0;
+
+void* operator new(std::size_t n)
+{
+  bytes_allocated += n;
+  return std::malloc(n);
+}
+
+void operator delete(void* p) noexcept { std::free(p); }
+#if __cpp_sized_deallocation
+void operator delete(void* p, std::size_t) noexcept { std::free(p); }
+#endif
+
+void
+test01()
+{
+#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+  std::wstring s0;
+  std::wstring s1 = L"/";
+  std::wstring s2 = L"///";
+  std::wstring s3 = L"file";
+  std::wstring s4 = L"C:";
+  std::wstring s5 = L"\\";
+#else
+  std::string s0;
+  std::string s1 = "/";
+  std::string s2 = "///";
+  std::string s3 = "file";
+  std::string s4 = "C:";
+  std::string s5 = "\\";
+#endif
+
+  using std::filesystem::path;
+
+  bytes_allocated = 0;
+  path p0 = std::move(s0);
+  VERIFY( bytes_allocated == 0 );
+  path p1 = std::move(s1);
+  VERIFY( bytes_allocated == 0 );
+  path p2 = std::move(s2);
+  VERIFY( bytes_allocated == 0 );
+  path p3 = std::move(s3);
+  VERIFY( bytes_allocated == 0 );
+  path p4 = std::move(s4);
+  VERIFY( bytes_allocated == 0 );
+  path p5 = std::move(s5);
+  VERIFY( bytes_allocated == 0 );
+}
+
+int
+main()
+{
+  test01();
+}
diff --git a/libstdc++-v3/testsuite/experimental/filesystem/path/construct/90634.cc b/libstdc++-v3/testsuite/experimental/filesystem/path/construct/90634.cc
new file mode 100644
index 0000000..6dce1df
--- /dev/null
+++ b/libstdc++-v3/testsuite/experimental/filesystem/path/construct/90634.cc
@@ -0,0 +1,75 @@
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-DUSE_FILESYSTEM_TS -lstdc++fs" }
+// { dg-do run { target c++11 } }
+// { dg-require-filesystem-ts "" }
+
+#include <experimental/filesystem>
+#include <cstdlib>
+#include <testsuite_hooks.h>
+
+std::size_t bytes_allocated = 0;
+
+void* operator new(std::size_t n)
+{
+  bytes_allocated += n;
+  return std::malloc(n);
+}
+
+void operator delete(void* p) noexcept { std::free(p); }
+#if __cpp_sized_deallocation
+void operator delete(void* p, std::size_t) noexcept { std::free(p); }
+#endif
+
+void
+test01()
+{
+#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
+  std::wstring s0;
+  std::wstring s1 = L"/";
+  std::wstring s2 = L"file";
+  std::wstring s3 = L"C:";
+  std::wstring s4 = L"\\";
+#else
+  std::string s0;
+  std::string s1 = "/";
+  std::string s2 = "file";
+  std::string s3 = "C:";
+  std::string s4 = "\\";
+#endif
+
+  using std::experimental::filesystem::path;
+
+  bytes_allocated = 0;
+  path p0 = std::move(s0);
+  VERIFY( bytes_allocated == 0 );
+  path p1 = std::move(s1);
+  VERIFY( bytes_allocated == 0 );
+  path p2 = std::move(s2);
+  VERIFY( bytes_allocated == 0 );
+  path p3 = std::move(s3);
+  VERIFY( bytes_allocated == 0 );
+  path p4 = std::move(s4);
+  VERIFY( bytes_allocated == 0 );
+}
+
+int
+main()
+{
+  test01();
+}