I should have clarified before: I meant LLVM compilation speed, no the speed of the code generated by LLVM :)

I've edited my original comment to include the clarification.

Ah, Polly actually slows compilation speed. [0]

[0] http://polly.llvm.org/docs/Performance.html#compile-time-imp...

Polly is not part of LLVM, really.

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).