I've spent the past few hours looking through documentation for how to build rustc with a patched LLVM without success. Currently, the best I'm at is:

submodules = false
fast-submodules = false

And then build with:

./x.py build --stage 1 src/llvm src/libstd

But even that doesn't rebuild anything unless I rm -Rf build. Which completely loses incremental compilation results.

Is there any way to make this development workflow better? Rebuilding from scratch at every change is… painful.