Sounds awesome to me! When can you submit a patch? :-)
On Thu, Jun 14, 2012 at 4:36 AM, Daniel Pfeifer <dan...@pfeifer-mail.de>wrote: > Hi, > > In a private mailing with Dave Abrahams and Brad King I wrote a > proposal of how I imagine PCH support should be implemented. Brad > asked me to send it to this list for further discussion. > Please note that even though I use present tense in the proposal, > nothing descibed below is implemented yet. > We have a similar implementation for PCH [1], but the interface > differs to this proposal. > > [1] > https://github.com/ryppl/ryppl/blob/develop/cmake/Modules/RypplPrecompileHeader.cmake > > cheers, Daniel > > > > CMakeLists.txt changes > ---------------------- > There are new target properties PRECOMPILE_HEADER and > PRECOMPILE_HEADER_<config>. These properties may be set to a list of > header files: > > set_property(TARGET target APPEND PROPERTY PRECOMPILE_HEADER > <boost/spirit/karma.hpp> > "my/precompiled/header.h" > ) > > > changes to source files > ----------------------- > None. All source files should be written as if there was no PCH > support. That means that each file should include all the headers it > requires. Nothing more, nothing less. > > That especially means that source files should *NOT* include an > "all.h", "precompile.h", or "stdafx.h" file. Nothing breaks if they > do, but it may impact compile times if precompiled headers are not > supported. > > > file(s) to precompile > --------------------- > Special header files that contain all the system headers may be > created and added to the PRECOMPILE_HEADER property. However, the > system headers may also be added directly to PRECOMPILE_HEADER. > > If custom files are created, it is important to note that a special > PCH_SUPPORTED guard is *NOT* required. > > > What is done behind the scenes > ------------------------------ > CMake creates the actual header file that is going to be precompiled > during the config step inside the current binary directory. The > complete filename encodes the target name and the configuration (eg. > "${CMAKE_CURRENT_BINARY_DIR}/${target}_${config}_pch.hpp") and > contains one #include directive for each element in the > PRECOMPILE_HEADER/PRECOMPILE_HEADER_<config> list. If the element is > wrapped in angle brackets, it is included unmodified, otherwise the > *absolute path* is used in double quotes. The generated header file > for the above example may look like this: > > /* generated by CMake 2.8.x */ > #include <boost/spirit/karma.hpp> > #include "/home/daniel/workspace/foo/my/precompiled/header.h" > > > This header file is compiled before all object files of the target; ie > the object files depend on the compiled header. > > > MSVC specific > ------------- > MSVC requires a source file to compile the header. This source file is > generated by CMake alongside the header file and may be called > <target>_pch.cpp, for example. It contains just one line: an #include > directive that includes the configured header file. > > The precompiled header (pch_binary) is created by compiling the source > file (pch_source) with "/Yc\"${pch_header}\" /Fp\"${pch_binary}\"". > > For the MSVC IDE, pch_binary might be "$(IntDir)/${target}.pch". > > All other source files are compiled with "/Yu\"${pch_header}\" > /FI\"${pch_header}\" /Fp\"${pch_binary}\"". > > /Yc = create pch > /Yu = use pch > /FI = force include > /Fp = name pch binary > > > GCC specific > ------------ > In GCC the pch_binary is created by compiling the header file directly > (no extra source file is required). The pch_binary must be > "${pch_header}.pch", there is no way to change that. Here, it pays off > again that we generate the actual pch_header in the binary directory. > > The compile flags to compile the header are "-x c++-header" and the > output file must be set with "-o ${pch_binary}" > > All the other source files are compiled with "-include ${pch_header}" > (force include), it may also be a good idea to pass "-Winvalid-pch". > -- > > Powered by www.kitware.com > > Visit other Kitware open-source projects at > http://www.kitware.com/opensource/opensource.html > > Please keep messages on-topic and check the CMake FAQ at: > http://www.cmake.org/Wiki/CMake_FAQ > > Follow this link to subscribe/unsubscribe: > http://public.kitware.com/cgi-bin/mailman/listinfo/cmake-developers >
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