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I am trying to build a clang static checker that will help me identify path(s) to a line in code where variables of type "struct in_addr" (on linux) are being modified in C/C++ progrmas. So I started to build a tool that will find lines where "struct in_addr" variable are being modified (and will then attempt to trace path to such places). For my first step I felt I only need to work with AST, I would work w/ paths as step 2.

I started with the "LoopConvert" example. I understand it and am making some progress, but I can't find how to only make the "LoopConvert" example in he cmake|build eco system. I had used

cmake -DCMAKE_BUILD_TYPE=Debug -G "Unix Makefiles"

when I started. I find that when I edit my example and rebuild (by typing "make" in the build directory) the build systems checks everything, seems to rebuilding quite a bit though nothing else has changed but 1 line in LoopConvert.cpp, and takes forever.

How can only rebuild the one tool I am working on? If I can shorten my edit-compile-test cycle I feel I can learn more quickly.

Gregory Hines
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  • I have since learned that using Ninja solves a lot of my problems. cmake -DCMAKE_BUILD_TYPE=Debug -G Ninja produces a ninja based build system that does NOT do excessive recompilations. Either Unix make is inadequate (unlikely?) or the way cmake produces Unix makefiles is suboptimum. Please use Ninja if you are having this issue. – Gregory Hines Jul 30 '20 at 15:28

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In a comment you say that switching to Ninja helped. I'll add my advice when using make.

First, as explained in an answer to Building clang taking forever, when invoking cmake, pass -DCMAKE_BUILD_TYPE=Release instead of -DCMAKE_BUILD_TYPE=Debug. The "debug" build type produces an enormous clang executable (2.2 GB) whereas "release" produces a more reasonable size (150 MB). The large size causes the linker to spend a long time and consume a lot of memory (of order 10 GB?), possibly leading to swapping (it did on my 16 GB VM).

Second, and this more directly addresses the excessive recompilation, what I do is save the original output of make VERBOSE=1 to a file, then copy the command lines that are actually relevant to what I am changing (compile, archive, link) into a little shell script that I run thereafter. This is of course fragile, but IMO the substantially increased speed is worth it during my edit-compile-debug inner loop.

I have not tried Ninja yet, but have no reason to doubt your claim that it works much better. Although, again, I think you want build type to be release for faster link time.

Scott McPeak
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