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    <div class="moz-cite-prefix">Hi Gabor!<br>
      <br>
      Yes, your guess is right. This work is XTU-related.<br>
      We didn't see any performance improvements, however. But Android's
      ASTs have the size reduction to 38Gb from 70Gb. I think it's a
      nice improvement.<br>
      <br>
      <br>
      21.10.2016 22:13, Gábor Horváth via cfe-dev пишет:<br>
    </div>
    <blockquote
cite="mid:CAPRL4a2p26KxiwVeY3f2JJhy6q5opczaWA2sRhKYX8wmG6XGFg@mail.gmail.com"
      type="cite">
      <div dir="ltr">Hi!<br>
        <div>
          <div class="gmail_extra"><br>
            <div class="gmail_quote">On 20 October 2016 at 18:12, Mehdi
              Amini via cfe-dev <span dir="ltr"><<a
                  moz-do-not-send="true"
                  href="mailto:cfe-dev@lists.llvm.org" target="_blank">cfe-dev@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"><span
                  class=""><br>
                  > On Oct 20, 2016, at 2:23 AM, Ilya Palachev via
                  cfe-dev <<a moz-do-not-send="true"
                    href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>>
                  wrote:<br>
                  ><br>
                  > Hi,<br>
                  ><br>
                  > It seems that compressing AST files with simple
                  "gzip --fast" makes them 30-40% smaller.<br>
                  > So the questions are:<br>
                  > 1. Is current AST serialization format really
                  non-compressed (only abbreviations in bit stream
                  format)?<br>
                  > 2. Is it worthwhile to compress AST by default
                  (with -emit-ast)?<br>
                  > 3. Will this break things like PCH?<br>
                  > 4. What's the current trade-off between PCH
                  compile time and disk usage? If AST compression makes
                  compilation a bit slower, but reduces the disk usage
                  significantly, will this be appropriate for users or
                  not?<br>
                  <br>
                </span>Is there a need for this disk usage? If the main
                use of AST files is C++ modules / PCH, what is a typical
                size for a module cache directory?<br>
                (Compression is expensive)<br>
              </blockquote>
              <div><br>
                <br>
              </div>
              <div>In some cases compression can actually improve the
                peformance, because in some cases the bottleneck is the
                I/O, and less data read from the disk and a fast
                decompression can be beneficial to the overall
                performance. <br>
                <br>
              </div>
              <div>In case someone wants to do a whole project analysis
                on merged ASTs, this compression can be a very
                significant saving. Dumping all of LLVM and Clang TUs to
                the disk occupies about 45 GB of disk space at the
                moment.<br>
              </div>
              <div><br>
                 </div>
              <blockquote class="gmail_quote" style="margin:0 0 0
                .8ex;border-left:1px #ccc solid;padding-left:1ex">
                <br>
                —<br>
                Mehdi<br>
                <div class="HOEnZb">
                  <div class="h5"><br>
                    <br>
                    ><br>
                    > LLVM already has a support for compression
                    (functions compress/uncompress in
                    include/llvm/Support/<wbr>Compression.h).<br>
                    ><br>
                    > Best regards,<br>
                    > Ilya Palachev<br>
                    > ______________________________<wbr>_________________<br>
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