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C-Reduce is a tool that takes a large C or C++ program that has a property of interest (such as triggering a compiler bug) and automatically produces a much smaller C/C++ program that has the same property. It is intended for use by people who discover and report bugs in compilers and other tools that process C/C++ code.

NOTE: C-Reduce happens to do a pretty good job reducing the size of programs in languages other than C/C++, such as JavaScript and Rust. If you need to reduce programs in some other language, please give it a try.

Documentation and other information can be found at the C-Reduce web page




  1. When set to use more than one core, C-Reduce can cause space in /tmp to be leaked. This happens because sometimes C-Reduce will kill a compiler invocation when a result that is computed in parallel makes it clear that that compiler invocation is no longer useful. If the compiler leaves files in /tmp when it is killed, C-Reduce has no way to discover and remove the files. You will need to do this manually from time to time if temporary file space is limited. The leakage is typically pretty slow. If you need to avoid this problem altogether, you can run C-Reduce on a single core (using --n 1) in which case C-Reduce will never kill a running compiler instance. Alternatively, a command line option such as -pipe (supported by GCC) may suppress the creation of temporary files altogether. Another possibility is to set the TMPDIR environment variable to something like /tmp/creduce-stuff before invoking C-Reduce -- assuming that the tools you are invoking respect this variable.

  2. Each invocation of the interestingness test is performed in a fresh temporary directory containing a copy of the file that is being reduced. If your interestingness test requires access to other files, you should either copy them into the current working directory or else refer to them using an absolute path.