[PATCH] Micro-optimization to avoid creating temporary path

[Jonathan Wakely]

Now that path::operator/=(basic_string_view<value_type>) works directly
from the string argument, instead of constructing a temporary path from
the string, it's potentially more efficient to do 'path(x) /= s' instead
of 'x / s'. This changes the only relevant place in the library.

        * src/filesystem/std-dir.cc (filesystem::_Dir::advance): Append
        string to lvalue to avoid creating temporary path.

Tested x86_64-linux, committed to trunk.


commit e48b1b71c76d12f999d9cf4a12239845281a26e4
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Tue Dec 18 15:39:12 2018 +0000

    Micro-optimization to avoid creating temporary path
    
    Now that path::operator/=(basic_string_view<value_type>) works directly
    from the string argument, instead of constructing a temporary path from
    the string, it's potentially more efficient to do 'path(x) /= s' instead
    of 'x / s'. This changes the only relevant place in the library.
    
            * src/filesystem/std-dir.cc (filesystem::_Dir::advance): Append
            string to lvalue to avoid creating temporary path.

diff --git a/libstdc++-v3/src/filesystem/std-dir.cc 
b/libstdc++-v3/src/filesystem/std-dir.cc
index 038f635a712..216182a2e56 100644
--- a/libstdc++-v3/src/filesystem/std-dir.cc
+++ b/libstdc++-v3/src/filesystem/std-dir.cc
@@ -61,7 +61,9 @@ struct fs::_Dir : _Dir_base
   {
     if (const auto entp = _Dir_base::advance(skip_permission_denied, ec))
       {
-       entry = fs::directory_entry{path / entp->d_name, get_file_type(*entp)};
+       auto name = path;
+       name /= entp->d_name;
+       entry = fs::directory_entry{name, get_file_type(*entp)};
        return true;
       }
     else if (!ec)