<div dir="rtl"><div dir="ltr">Are you talking about the local (static) function make_absolute, not the llvm::sys::fs::make_absolute ?</div><div dir="ltr"><br></div><div dir="ltr">Anyhow, StringRef p() is not constructed from the Twine current_directory but from the SmallVector &path which is the relative path to being made absolute, .This StringRef(SmallVector) construction should be zero-cost. </div><div dir="ltr"><br></div><div dir="ltr">The Twine current_directory is constructed only later, if use_current_directory. It may still be possible to optimize this code path but first check how much the use_current_directory=true is code path used vs the use_current_directory=false code path.</div><div dir="ltr"><br></div><div dir="ltr"><br></div></div><div class="gmail_extra"><br><div class="gmail_quote"><div dir="ltr">2016-04-19 0:55 GMT+03:00 <Alexander G. Riccio> via llvm-dev <span dir="ltr"><<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>></span>:</div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><font face="monospace, monospace">llvm::sys::fs::make_absolute</font> converts its first parameter (<font face="monospace, monospace">const Twine ¤t_directory</font>) to <font face="monospace, monospace">StringRef p(path.data(), path.size())</font>, and then passes that <font face="monospace, monospace">StringRef</font> to several functions (<font face="monospace, monospace">path::has_root_directory</font>, <font face="monospace, monospace">path::has_root_name</font>, and <font face="monospace, monospace">path::append</font>) that accept <font face="monospace, monospace">Twines</font> as parameters. Since <font face="monospace, monospace">llvm::StringRef</font> can implicitly convert to an <font face="monospace, monospace">llvm::Twine</font>, <font face="monospace, monospace">p</font> converts to a bunch of <font face="monospace, monospace">Twine</font> temporaries.<div><br></div><div>In a few places, namely <font face="monospace, monospace">path::has_root_directory</font> & <font face="monospace, monospace">path::has_root_name</font>, that temporary <font face="monospace, monospace">Twine</font> is again converted to a <font face="monospace, monospace">StringRef</font>:</div><div><br></div><div><div><font face="monospace, monospace">bool has_root_directory(const Twine &path) {</font></div><div><font face="monospace, monospace"> SmallString<128> path_storage;</font></div><div><font face="monospace, monospace"> StringRef p = path.toStringRef(path_storage);</font></div><div><font face="monospace, monospace"><br></font></div><div><font face="monospace, monospace"> return !root_directory(p).empty();</font></div><div><font face="monospace, monospace">}</font></div><div><br></div><div>Is there some reason for this? If not, I'll write a patch to delay the <font face="monospace, monospace">StringRef p(path.data(), path.size())</font> construction until it's actually needed (calls to <font face="monospace, monospace">path::root_name(p)</font> & <font face="monospace, monospace">path::relative_path(p)</font>).</div><div><br clear="all"><div><div><div dir="ltr"><div><div dir="ltr"><span style="font-size:12.8px">Sincerely,</span><br style="font-size:12.8px"><span style="font-size:12.8px">Alexander Riccio</span><br style="font-size:12.8px"><span style="font-size:12.8px">--</span><br style="font-size:12.8px"><span style="font-size:12.8px">"Change the world or go home."</span><div style="font-size:12.8px"><a href="http://about.me/ariccio" target="_blank">about.me/ariccio</a></div><div style="font-size:12.8px"><a href="http://about.me/ariccio" target="_blank"><br></a></div><div style="font-size:12.8px">If left to my own devices, I will build more.</div><div style="font-size:12.8px">⁂</div></div></div></div></div></div>
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