A bit of fun on the side: Compiling with Clang

In the other bit of spare time I have considered looking at compiling FreeCAD using Clang. The end result is that only a few changes are needed to be made to the FreeCAD source so that it compiles with Clang.It doesn't seem to affect building using g++ either. I haven't measured the performance yet, but noticeably compiling takes less time.

I still need to collect these changes and post a patch for this and allow other people to test it out for themselves. I also have to find how I can debug FreeCAD after compiling with Clang - it appears to be incompatible with GNU's gdb.

Other Progress (slightly off-topic):

Workload seems to have increased once again at University. I spent a bit more time at the weekend on the Drawing Module: the majority of the work is looking at projecting faces onto the drawing plane. This is relatively similar to before but requires further work to sort edges into order, store these in a general format and then drawing using Qt's painter system. There's still work to do, but when I get that complete can hopefully share it.

What is Clang?

Clang is an alternative compiler that use LLVM to compile a variety of programming langaguesusing runtime optimisation methods. LLVM is used heavily in Mac OS X to improve graphics performance applications, but is also used in a handful of open source projects - in particular Open Source graphics drivers. LLVM provides the possibility to compile many different programming languages from Python, Fotran, OpenCL and importantly for this post c / c++.

Clang provides the infrastructure for compiling c++ and aims to offer a better alternative to gnu's gcc in terms of performance, better usability to developers and other advanced features such as static code checking. I won't say much more, but it seems a good alternative and therefore I decided to look at compiling FreeCAD using Clang.

What I did?

1. Install Clang
2. Change default compiler for make tool chain
3. Change some of the check inside CMakeList.txt file
4. (Ubuntu) Add a symlink for libgfortran for the linker to correctly work

Selecting the default compiler for your system (Ubuntu)

Most importantly install clang on your system. It seems that with Ubuntu installing clang introduces a an unwanted dependency of  gcc 4.6. Once installed, depending on your system you can inform Cmake explicitly to use clang or alternatively you can change the system wide default for make to use the clang compiler.The first option is obviously the most sensible, but I am not sure of the command.

The only help I have seen on setting the compiler is the following stackoverflow question:

In Ubuntu, it is straighforward to update the system wide compiler use for c++, simply run

sudo update-alternatives --config c++

This will bring up an interface to select the compiler you wish to use:

I need to post the patches to CMake, hopefully soon and these can be verified by other users. 

Following this, configure using cmake and then attempt to build using clang. You may notice that there is a linking error for lgfortran and then the build system fails. I think this is an issue with Ubuntu, but to solve this I had to create a symlink to gfortran library which isn't very convenient.

sudo ln -s /usr/lib/gcc/x86_64-linux-gnu/4.7/libgfortran.so libgfortran.so

Hopefully FreeCAD should happily compile very fast now at blinding speed!

----Update---

I have spent some time last week to look at some further details.

Compiling using Clang per project:

There is an advanced option within CMake to specify what compiler to use for c and c++ per project build. Fortunately KDevelop makes this rather easy: Open Project Configuration by right clicking on the project to open the following dialog:

Click 'Show Advanced Values' and then set the following variable:

• CMAKE_CXX_COMPILER  = /usr/bin/clang++ 
• CMAKE_C_COMPILER to /usr/bin/clang

Compiler flags can be conveniently set in CMAKE_CXX_FLAGS, where for both gnu compiler and clang -g is for full debug.

Specifying Variables in the command line

It can also be done in the command line - I found really straightforward Guide for setting Variables in Cmake from (http://www.llvm.org/docs/CMake.html#id8)

Variables are set quite easily - simply prepend -D before the variable name and assign the value like so

cmake -DVARIABLE=value

Alternatively, you can specify the type of the variable below:

cmake -DVARIABLE:TYPE=value

Debugging with Clang:

Unfortunatly there is currently a bug that is preventing gdb being used with clang, which is apparently fixed in the latest release. I tried to get this too compile but I encountered errors. Hopefully with the next release of LLVM and Clang 3.3, the issue will be resolved. 

Using KDevelop to develop FreeCAD

Some hard core people bring themselves to use just a text editor, whether its VIM, or a standard desktop editor from Kate, GEdit. These have their places but when you're learning programming or working with large project, it's much quicker to have syntax highlighting/checking and code hinting so that you don't have to trudge through programming documentation. The additional tools for compiling make life much easier too.

One option is to look at the DOXYGEN documentation for FreeCAD. It's seldom used because its both incomplete and it's difficult to navigate without knowing what you're explicitly looking for.

For c++ programming, there are two alternatives, either QtCreator or KDevelop atleast on Linux unless someone can name some viable alternatives. Admittedly QtCreator is very good and is feature complete, for some reason it is incompatible (at least momentarily) importing projects using CMake (a build system). This essentially means you cannot read the source project tree and get useful programming hints, which without I think makes learning FreeCAD much more difficult.

Once you've installed KDevelop, it's very easy to configure the compiler settings. It's in built debugger is extraordinary especially for a newbie to diagnose crashes and above all is built in. The syntax highlighting and code hinting is generally good too. My only dissatisfaction is that sometimes it gets into the habit of crashing, but it's not a problem since it can recover unsaved files.

Here's a quick guide to help you getting it up and running to make your own opinion!

Using KDevelop to develop FreeCAD:

 Firstly ensure that KDevelop is installed and you've got a copy of the FreeCAD source to work with. Load up KDevelop as follows:

Click on Import Project to import the FreeCAD sources.

A dialog will appear. Go to the root directory within the source and then browse for the CMake project file CMakeLists.txt and click 'next'

In the next section you can specify where the FreeCAD sources are built under Build Directory. You can also set the build type. I would always recommend using the Debug build type so that you can easily debug the program for any faults later. Selecting the Release option will provide extra compiler optimisations that will improve FreeCAD's performance, but only significantly in certain areas such as the Sketch Solver. The other two options I wouldn't recommend.

Click OK and KDevelop will start importing the whole project. Further compiler and project settings can be changed under Open Configuration.

If you click under Classes tool bar you can browse the whole source tree which including other library headers. The Flying pink bricks indicate public methods. Icons with Pad Locks are 'private' class members and icons with keys are 'protected methods'.

Open  up a source file (.cpp) and try out the code hinting by pressing CONTROL + SPACEBAR. This will bring up a list of methods below which the class provides. How easy is that?

It can even help suggest the variables, objects that can be passed as arguments into a method:

Make a few little changes and the proceed to click Build Selection. 

This should start configuring your project and it may hint problems. Otherwise normally it will show the build progress in the Build Window as below:

Remember to speed up the build by using multiple cores, append -j4 under the Additional Make Options found in Project->Open Configuration->Make. Compiling usually takes between 15-25 minutes on a good day. However sit back, grab a cup of tea or continuing programming.

Finally Running FreeCAD from Kdevelop

Before running you need to configure the launches. This can be found under Run-> Configure Launches. A new dialog will appear. Choosing the executable FreeCADMain is really straightforward

Now back in the main window you can hit Execute to run normally. Alternativly you can hit Debug to run the application through the GDB debugger. I'll describe how to use the debug tools later!

Hopefully that might help you get started to make tweaks and changes to FreeCAD!