This appears to be a performance regression. I have a non-standard compiler generating a large assembly file (60-70 MB). Some automated tools (cmake) will append the -g flag by default. With apple LLVM 10.0 (cc --version says Apple LLVM version 10.0.0 (clang-1000.10.44.4)) the following compiles fine: bash time cc -c -g -o file.o file.s real 0m24.527s user 0m20.760s sys 0m2.497s With apple LLVM 11.0.3 (cc --version says Apple clang version 11.0.3 (clang-1103.0.32.62)) and 12.0 (Apple clang version 12.0.0 (clang-1200.0.32.28)) the process hangs (the build process times out after 90 minutes in this case). The workaround is to remove the -g flag. Part of the problem is that the -g flag may be inserted by automated tools (cmake in particular). Tested on MacOS High Sierra and Catalina