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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>
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<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>
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