Polly is considered one of the "primary sub-projects of LLVM."
That said, it's generally not seen as part of the main stack, which would be LLVM, Clang, compiler-rt, and maybe lld, libc++, and libc++abi. (The latter three being fully optional replacements where most people use the standard system components instead).
That said, it's generally not seen as part of the main stack, which would be LLVM, Clang, compiler-rt, and maybe lld, libc++, and libc++abi. (The latter three being fully optional replacements where most people use the standard system components instead).