[christina_b]

Regular LTO for large sized projects (think Chromium sized), in my experience is by far the biggest bottleneck in the build process. It's partially the reason so much is being invested into development and improving parallel linking as well as techniques like ThinLTO that all aim at reducing the link times since often, LTO linking takes around 60-70% of all build time combined despite the heavy use of C++ code (although with no exceptions or RTTI).

Unless you have build servers capable of rebuilding all Qt, WebKit etc. and performing an LTO link (which pulls in all build artifacts in form of bitcode archives/objects) in a reasonable amount of time (big reason buildlabs exist - it takes a long time), LTO is not likely to be suitable, it's an extremely expensive optimization that essentially defers all real compilation until the link step at which the linker calls back into libLLVM/libLTO and have them do all the heavy lifting.

At the very least you need a workstation grade machine to be able to do that kind of stuff on regular basis, you really can't expect everyone to have that. And there's a reason libLLVM.so is usually dynamically linked, it cuts a massive amount of time spent on builds, which is especially useful while developing and it's a middle ground between building all LLVM and Clang libraries as shared objects and having to wait for static linking of various LLVM modules into every LLVM toolchain binary (which tends to result in the toolchain being much much bigger). The build cache with shared libLLVM.so for Clang/LLVM/LLD builds is around 6-7GB (Asserts/Test builds). Statically linking LLVM modules blows that up to 20GB. God forbid you actually do a full debug build with full debug information with that.

That's a terrible argument against dynamic linking. That's not to say static linking is bad, in fact, recently it's been making a comeback for exactly that reason - LTO and next-generation optimizers. But saying LTO makes static linking viable for everyone including consumers is somewhat far fetched.

[jcelerier]

> At the very least you need a workstation grade machine to be able to do that kind of stuff on regular basis, you really can't expect everyone to have that. And there's a reason libLLVM.so is usually dynamically linked, it cuts a massive amount of time spent on builds, which is especially useful while developing

I of course do not argue doing LTO while developing, it seemed clear for me that the context of the whole thing is about what's released to users.