Complex sentence: LLVM can provide the middle layers of a complete compiler system, taking intermediate form (IF) code from a compiler and outputting an optimized IF that can then be converted and linked into machine-dependent assembly code for a target platform.
Split into simpler sentences: LLVM can provide the middle layers of a complete compiler system, taking intermediate form (IF) code from a compiler and outputting an optimized IF. This new IF can then be converted and linked into machine-dependent assembly code for a target platform.