Using GCC to find unreachable functions ("dead code")

Question

I was looking for a way of finding statically unreachable functions in a (very) big C++ project. I had tried using doxygen and other static analysis tools suggested here but it seemed that the project is too complicated for them to handle. Finally i decided that using GCC tools (g++, gprof, gcov, etc.) is the safest option, although I couldn't figure out how to do it.

I think the g++ optimizations eliminate statically unreachable functions but I'm not sure how to get the names of the functions it eliminates.

Do you have any suggestions?

Answer 1

Dead code optimization is typically done by the linker - the compiler doesn't have the overview. However, the compiler might have eliminated unused static functions (as they have internal linkage).

Therefore, you shouldn't be looking at GCC options, but at ld options. It seems you want --print-gc-sections. However, note that you probably want GCC to put each function in its own section, -ffunction-sections. By default GCC will put all functions in the same section, and ld isn't smart enough to eliminate unused functions - it can only eliminate unused sections.