<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Jan 4, 2016 at 12:36 PM, Benjamin Kramer via llvm-commits <span dir="ltr"><<a href="mailto:llvm-commits@lists.llvm.org" target="_blank">llvm-commits@lists.llvm.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="HOEnZb"><div class="h5">On Mon, Jan 4, 2016 at 9:26 PM, Xinliang David Li via llvm-commits<br>
<<a href="mailto:llvm-commits@lists.llvm.org">llvm-commits@lists.llvm.org</a>> wrote:<br>
> Author: davidxl<br>
> Date: Mon Jan  4 14:26:05 2016<br>
> New Revision: 256776<br>
><br>
> URL: <a href="http://llvm.org/viewvc/llvm-project?rev=256776&view=rev" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project?rev=256776&view=rev</a><br>
> Log:<br>
> [PGO]: reserve space for string to avoid excessive memory realloc/copy (non linear)<br>
><br>
> Modified:<br>
>     llvm/trunk/lib/ProfileData/InstrProf.cpp<br>
><br>
> Modified: llvm/trunk/lib/ProfileData/InstrProf.cpp<br>
> URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/ProfileData/InstrProf.cpp?rev=256776&r1=256775&r2=256776&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/ProfileData/InstrProf.cpp?rev=256776&r1=256775&r2=256776&view=diff</a><br>
> ==============================================================================<br>
> --- llvm/trunk/lib/ProfileData/InstrProf.cpp (original)<br>
> +++ llvm/trunk/lib/ProfileData/InstrProf.cpp Mon Jan  4 14:26:05 2016<br>
> @@ -168,6 +168,12 @@ int collectPGOFuncNameStrings(const std:<br>
>                                bool doCompression, std::string &Result) {<br>
>    uint8_t Header[16], *P = Header;<br>
>    std::string UncompressedNameStrings;<br>
> +  size_t UncompressedStringLen = 0;<br>
> +<br>
> +  for (auto NameStr : NameStrs)<br>
> +    UncompressedStringLen += (NameStr.length() + 1);<br>
> +<br>
> +  UncompressedNameStrings.reserve(UncompressedStringLen + 1);<br>
<br>
</div></div>This still does excessive copying, "auto NameStr" will create a copy<br>
of the string on every iteration.</blockquote><div><br></div><div>The patch was to solve the original problem of non-linear behavior -- but you are right using auto still causes overhead (where iterator based interface should be used).</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> Please just use join() from<br>
StringExtras.h instead of duplicating that code here.<br></blockquote><div><br></div><div>Great -- that is exactly the interface needed.</div><div><br></div><div>thanks,</div><div><br></div><div>David</div><div> <br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
- Ben<br>
<div class="HOEnZb"><div class="h5"><br>
><br>
>    for (auto NameStr : NameStrs) {<br>
>      UncompressedNameStrings += NameStr;<br>
><br>
><br>
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