Hi, Am Freitag, 11. August 2023, 22:14:13 CEST schrieb Marc Mutz via Development: > All my -unity-build-batch-size 100'000 patches except for one are now > merged: https://codereview.qt-project.org/q/topic:unity-build > > I'm currently testing without the unmerged one, because it won't apply > to 6.5, anyway, and the goal is to have unity-builds from 6.5 onwards. > Maybe a few more TUs will have to be excluded, but you should be able to > see the pattern. So far it looks like it's not needed. > > Compile with -unity-build -unity-build-batch-size 100000 and add all TUs > that create problems with a small comment as to what's breaking to > NO_UNITY_BUILD_SOURCES.
Just a quick note/question given 100000 seems to be used to denote "all the sources!": CMake actually supports "0" as value for that purpose of "all!", had that been considered in the design, to be consistent with CMake's approach? >From https://cmake.org/cmake/help/latest/prop_tgt/UNITY_BUILD_BATCH_SIZE.html --- 8< --- Although strongly discouraged, the batch size may be set to a value of 0 to combine all the sources for the target into a single unity file, regardless of how many sources are involved. This runs the risk of creating an excessively large unity source file and negatively impacting the build performance, so a value of 0 is not generally recommended. --- 8< --- Curiousity: While at it, I am curious what purpose unity builds of Qt are supposed to serve, i.e. in which cases would exclusive use of unity builds be recommended to be used? Are there some docs/notes somewhere, when to use and when not? Personally had been very impressed by the speed up when I first learned about the concept decades ago (KDE's --enable-final flag with unsermake IIRC) and the compiler at that time having more options to optimize the generated code. But with LTO these days, by what I understood, that advantage/purpose is gone. And while I made some own project recently work with cmake unity builds for curiousity (thus knew about that special value "0" for batch sizes :) ) I am still wondering when actually unity builds make sense to be used, especially in parallel with supporting non-unity builds. So, for which use cases are Qt's unity builds done? Whom will the docs recommend to use that build option? Cheers Friedrich -- Development mailing list Development@qt-project.org https://lists.qt-project.org/listinfo/development
