I am tweaking LLVM files and do a "make" in my build director to rebuild LLVM with the tweaked files, which is taking a while even though my changes were rather small (I understand that my one file will be affect other files). Do I have to use 'cmake --build .' to generate a new make file in the build directory or is it right to just call 'make'. And is it common for rebuilds to take a while?
I think, most time is spent re-linking the binaries, of which LLVM has many (opt, llc, etc.). One option to speed up the build is to enable LLVM_BUILD_LLVM_DYLIB and LLVM_LINK_LLVM_DYLIB and the other is to issue make opt instead of make, if you are mostly working with opt.
These options would make build system produce a single giant dynamic library (.so or .dll) containing all LLVM components (LLVMSupport, LLVMCodegen, etc), and make tools link to it. Linking to a dynamic library is much faster, because you don't need to re-link all the static code for each tool executable.