What does the clang -cc1 option do?

Question

I\'m a newbie in clang. I have read a paper about source to source transformation from cuda to opencl using clang compiler fr

Answer 1

The usual compiler consists of so-called compiler driver, which knows how to execute compiler itself, assembler, linker, etc. and compiler itself which just takes the source code (sometimes already preprocessed) and emit assembler/object code.

Clang implements all these components in the single binary, the difference is just the cmdline. Here clang -cc1 invokes the compiler itself with its internal/undocumented set of options, etc.