** Work In Progress **
Transparency about my course work: When you are reading the document below if you by any chance get into the feeling that I am trying to take advantage of the open source community for my course work, please come back and read this again. Initially my thought was to keep all the course work specific code in a separate private branch, which I would not push to this repository. The reason for that was, that branch had some materials that are totally irrelevant in public like my progress report, etc. But with this private branch approach, it looks like it is hard to convince open source contributors that I am not trying to get the grades from their work. So I have decided to make the branch public here and the branch is called course-specific. I will be merging course-specific branch to master whenever there is something relevant to master committed to that branch but in the other direction I will only cherry-pick my changes from master to course-specific.
What is this all about?
This is a very humble attempt to implement a compiler in Python. Prof. Michael Franz (http://www.ics.uci.edu/~franz/) offers a graduate level course at University of California, Irvine, on Advanced Compiler Construction (http://www.ics.uci.edu/~franz/Site/w12cs241.html). This compiler is being written as part of the course work. Although I have a very limited knowledge about compiler construction, I believe that this compiler implements some of the most basic components that are expected of any reasonable compiler today.
While implementing this compiler I stumbled upon certain interesting concepts in compiler construction. I could not find simple and quickly understandable materials for many of them. In most cases it boiled down to reading the original papers that introduced the idea, toiling for days to understand how the concepts introduced in the paper worked before actually sitting down to implement that concept. I hope that I can be of some help to others who are trying to do the same. So while implementing these algorithms I have spent good amount of time to make the code as readable as possible And what more, it is written in Python! What is more readable than Python anyway!?
I would really like to make this a repository of algorithms that are used in writing compilers today. So if you would like to use these algorithms or think you can improve them further, fork it away! And if you want to push those changes back to this repository, I will be happy to merge the pull requests!
What is the status? Is this compiler complete?
The compiler compiles the code to x86_64 binary. But the compiler in place is only a very basic version. There is so much more to do. If you are interested in contributing, please contact one of the authors.
Which programming languages is this compiler written for?
As it is required for the course, at the moment this compiler is planned to compile only PL241. I am not sure about the copyrights of the Professor's material to put the language spec here. So the document that contains the spec for the language is available from the Professor's website at http://www.ics.uci.edu/~franz/Site/2012WinterCS241/2012CS241Project.pdf
In the future I would like to make this a compiler collection for major languages.
What are the target architectures to which this compiler generates binaries?
Only x86_64 is planned at the moment. Most ideally I would like to see how this runs on RISC architectures like ARM.
What additional libraries are required to run this compiler?
Since the register allocator is implemeted using an off-the-shelf SAT solver (which is hard coded to be glucose at the moment, you will have to download the source code from glucose's website: http://www.lri.fr/~simon/?page=glucose and compile the source. The binary should be available on your system path and with the exact name glucose_static.
Other than this and the standard Python 2.7 installation, you will not want any additional libraries. Deliberate care has been taken not to use any other third-party libraries. However, since argparse is used for command line parsing, Python 2.6 or earlier doesn't work. But argparse component can be very easily replaced with the older optparse library code which is at the end of each file in the bootstrap() function.
This code has not been tested on Python 3.x.
How to compile the code?
The source program can be compiled by running the following command:
$ pl241c.py [options] <source-file-name>
The options available at the moment are:
usage: pl241c.py [-h] [-a] [--cfg] [--interferencevcg] [--optimized] [--optimizedvcg] [-p] [-r] [--regassigned] [-s] [--ssavcg] [-t] [--virtualreg] [--virtualregvcg] File Names [File Names ...] Compiler arguments. positional arguments: File Names name of the input files. optional arguments: -h, --help show this help message and exit -a, --dumpall Dump all the intermediate files and graphsgenerated. --cfg Generate the Visualization Compiler Graph output of the Control Flow Graph. --interferencevcg Generate the Visualization Compiler Graph of the interference graph. --optimized Generates the ouput of the optimizer. --optimizedvcg Generate the Visualization Compiler Graph output of the optimized SSA. -p, --parsetreevcg Generate the Visualization Compiler Graph output of the parse tree. -r, --ir Generate the Intermediate Representation. --regassigned Generate the instructions with registers and phi functions resolved. -s, --ssa Generate the Static Single Assignment. --ssavcg Generate the Visualization Compiler Graph output of the SSA form. -t, --dom Generate the Dominator Tree VCG output. --virtualreg Allocate registers in the virtual space of infinite registers. --virtualregvcg Generate the Visualization Compiler Graph for the virtual registers allocated and liveness computed for the subgraphs.
For convenience, 3 test programs are supplied along with the source of which two of them intentionally include syntax errors. firsttest.pl241 is expected to generate binary.
What are the things that this compiler does?
The the source program is parsed and translated to an Intermediate Representation (IR) and then transformed again to Static Single Assignment (SSA) form. A few very simple yet powerful optimizations: Common Sub-expression Elimination, Copy Propagation and Constant Folding are implemented. A register allocator is implemented using an off-the-shelf SAT solver called GLUCOSE. Then the program is deconstructed out of SSA form and x86_64 machine code is generated from those instructions.
What algorithms are implemented?
- The parser is a home-brewn solution. It doesn't use lex and yacc, however it does make use of regular expressions.
- "A Fast Algorithm for Finding Dominators in a Flowgraph" by T. Lengauer and R. E. Tarjan
- "Efficiently Computing Static Single Assignment Form and the Control Dependence Graph" by R. Cytron, J. Ferrante, B. K. Rosen, M. N. Wegman and F. K. Zadeck
As mentioned in the previous sections it will be nice to see at least the following implemented
- Parsing major programming languages
- Generating binaries for ARM
- Various optimization algorithms
- Instruction scheduling
- Various types of register allocation algorithms
If you are interested in contributing, send the pull requests!