Default build type: Release or Debug?

[menon-karthik]

Problem

If I'm not mistaken, the default build type is now Debug and used to be Release. I don't know if/when this actually changed. But we should probably make this easier for the user to see and/or change. For a user who does not know this, they could be accidentally using a debug build, which (from a rigorous study with N=1) could be close to 100x slower.

Solution

• Include details in the documentation on how to switch between Release and Debug builds (and why)
• Print a message in CMakeLists clarifying what the current build is

Additional context

I tested this on an M4 Mac, building from source. I would like to hear from others if the default build type is different for different ways of building. @mrp089 @ktbolt since you built on different systems (for the SimTK binaries maybe?), do you know if it is always debug?

Code of Conduct

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[ktbolt]

@menon-karthik On MacOS Ventura M2 I don't see that BUILD_TYPE is even set. Why do you think the BUILD_TYPE is Debug ?

[menon-karthik]

@ktbolt It prints debug messages from solve/debug.h only in DEBUG mode, and it is printing those messages for me by default (without the build type being specified, as you said). Also, I specified a Release build with -DCMAKE_BUILD_TYPE=Release and the debug messages stopped getting printed and the simulation ran 100x faster.

That's why I posted this issue; I was curious to see if it's platform-dependent when it isn't explicitly specified.

I think it's a good idea to specify Release as the default. What do you think?

[menon-karthik]

@ktbolt Also, going down this rabbit-hole made me think it is platform-dependent, but I might be wrong: https://stackoverflow.com/questions/24460486/cmake-build-type-is-not-being-used-in-cmakelists-txt

[ktbolt]

@menon-karthik I have to use cmake -DCMAKE_BUILD_TYPE:STRING=RELEASE to see the c++ -O3 option so it seems that by default the build uses -O0 (no optimization). Oops.

The other solvers set CMAKE_BUILD_TYPE to RelWithDebInfo which uses the c++ -O2 option.

[menon-karthik]

Update: The documentation does specify the build type using cmake -DCMAKE_BUILD_TYPE=Release ... I guess I wan't looking at the documentation myself :)

@ktbolt should this be left as-is or do you want to still specify the default build type in CMakeLists?

[ktbolt]

@menon-karthik I was also not aware of needing to use -DCMAKE_BUILD_TYPE=Release when building the installers. This is a good find !

We should make the default CMAKE_BUILD_TYPE something reasonable like RelWithDebInfo. All the other solvers do this. This will use an O2 optimization which is typically fine.

However, Eigen may be able to run faster with O3 optimization which is used when the CMAKE_BUILD_TYPE is Release but I've seen that this level of optimization can sometimes cause problems and can potentially produce slower executions times. This may also be platform dependent, need to test this.