Reducing C/C++ code

Once in a while I run into internal compiler errors. To provide a nice minimal test case with the bug report I still use DustMite. It was actually written for D code but works good enough for C++ as well and is easier to setup than more sophisticated tools like C-Reduce. Just get the LDC compiler and compile DustMite with ldc2 -O3 -release -g dustmite.d splitter.d.

Then put all your test sources in one folder. Sometimes it makes sense to get a preprocessed version of your code first (-E or /EP option).

Create a test script outside this folder with the test commandline that reproduces the error:

cl -c -O1 test.c 2>&1 | "C:\Program Files\Git\usr\bin\grep.exe" -q "internal error"

Here I’m using the grep utility Git for Windows provides.

Now we can let DustMite work its magic: dustmite --split "*.{c,cpp,h,hpp}:d" test ..\make.bat. Make sure to run it from a proper environment, like the Native Tools Command Prompt for msvc.

It will take a while but when it’s all done you should have a reduced test case. Some post-processing may still be necessary as DustMite only uses a simple splitter and can’t do advanced transformations that would require knowledge about C++.