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<div id="smartTemplate4-template">I want to try in following way.
Would you please check if it is feasible for me?<br>
<br>
1. For each .h file, I generate one PCH file;<br>
<br>
2. When I generate a PCH file, I store its included .h files (with
full path information) in the PreprocessorOpt.Includes<br>
<br>
3. When I open a source code, say xxx.cpp file to parse, in the
PPCallback function for each #include in xxx.cpp, I check if there
is a corresponding PCH file. If no, I first generate the PCH file.
Then load the PCH file using ASTReader.<br>
<br>
4. When I load a PCH file, I use ASTReaderListener to check if
there are any #includes in the PCH's PreprocessorOpt.Includes. If
so, I load those PCHs first. This can be a nested invocation of
the ASTReaderListener. In this way, I hope the chained includes
can be implemented.<br>
<br>
5. After loading a PCH file, I use ASTReader's InitializeSema and
ASTContext.setExternalSource, so the preprocessor can find all the
identifiers defined in the PCH.<br>
<br>
Why I use one PCH for each .h file is because I can compare the
two files' time to verify if the source .h is changed. If changed,
I have to generate a new PCH for it. Do you know any information
stored in a PCH I can use for this purpose?<br>
<br>
Thank you so much!<br>
-Yao<br>
<br>
<br>
<br>
On Tue, Aug 13, 2013 at 6:08 PM, Eli Friedman
<a class="moz-txt-link-rfc2396E" href="mailto:eli.friedman@gmail.com"><eli.friedman@gmail.com></a> wrote:<br>
</div>
<br>
<blockquote
cite="mid:CAJdarcFNkiez6gLvkeZ5-NDT52nAFgA61S1GGiR6vkTpm-xtBA@mail.gmail.com"
type="cite">
<div dir="ltr">On Tue, Aug 13, 2013 at 6:19 AM, Yao SHEN <span
dir="ltr"><<a moz-do-not-send="true"
href="mailto:yaoshen@andrew.cmu.edu" target="_blank">yaoshen@andrew.cmu.edu</a>></span>
wrote:<br>
<div class="gmail_extra">
<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">Hello,<br>
<br>
This is Yao Shen. I got a problem recently and hope
someone here can help me.<br>
<br>
I am using llvm+clang to parse c/c++ codes. My objective
is to do some instrumentations towards these codes by
inserting instructions into the codes.<br>
<br>
The problem is: the codes are somewhat large. They usually
larger than 50M. And there are a lot of header files
shared by c/c++ files. All of these make the parsing
process very slowly (> 30 minutes).<br>
<br>
So I am think if I can use PCH. In the first step, I will
compile all of the header files into PCHs. And then when
parsing c/c++ files, I load corresponding PCH files in the
PPCallback using ASTReader. It works when the header file
is simple (not including other headers). However, if there
is a chained including, it cannot work.<br>
<br>
For example, if A.h includes B.h, and if I first convert
B.h into B.h.pch, and A.h into A.h.pch, then when parsing
main.c which includes A.h, the identifiers in B.h cannot
be recognized. And if the main.c include both A.h and B.h,
the parse will not pass successfully even if I use
#ifdef... in B.h to avoid redefinitions.<br>
<br>
Maybe I have to use chainedincludesSource. However, there
is few guides I can get. I don't know how to use it.<br>
<br>
Is there anyone who can help? Do you think using
PPCallback::InclusionDirective is a right way in this
situation?<br>
<br>
</blockquote>
<div><br>
</div>
<div>You might want to consider modifying your source code
to use modules; see <a moz-do-not-send="true"
href="http://clang.llvm.org/docs/Modules.html">http://clang.llvm.org/docs/Modules.html</a>
. Alternatively, instead of compiling individual headers
using PCH, you could precompile one big header which
includes all the commonly used headers in your project.</div>
<div><br>
</div>
<div>This is a hard problem; if it were easy, clang would do
it for you already. :)</div>
<div><br>
</div>
<div>-Eli</div>
</div>
</div>
</div>
</blockquote>
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