[NFC] Fixing dependency to C++17

[NFC] fixing merge conflicts

[NFC] Fixing conflict issue

[NFC] mergin temp branch and main

[NFC] fixing NITs

[NFC] Decoupling the unrolling logic
Decoupling the unrolling logic into three different functions. The shouldPragmaUnroll() covers the 1st and 2nd priorities of the previous code, the shouldFullUnroll() covers the 3rd, and the shouldPartialUnroll() covers the 5th. The output of each function, Optional<unsigned>, could be a value for UP.Count, which means unrolling factor has been set, or None, which means decision hasn't been made yet and should try the next priority.

[NFC] Decoupling the unrolling logic into three different functions. The shouldPragmaUnroll() covers the 1st and 2nd priorities of the previous code, the shouldFullUnroll() covers the 3rd, and the shouldPartialUnroll() covers the 5th. The output of each function, Optional<unsigned>, could be a value for UP.Count, which means unrolling factor has been set, or None, which means decision hasn't been made yet and should try the next priority.

[WIP][NFC] Changing bool, as the return arg of unrolling logics, to optional<unsigned>

[WIP][NFC] Cleaning the params of functions --draft

[WIP][NFC]Seperating setting UP.count from other side parameters

[WIP][NFC] factor out unrolling decision logic

"Adding ShouldContinue as the return value of unrolling logic"

In D105173#2861546, @dmgreen wrote:

The latest revision appears to be missing most of the changes. You may want to squash several commits together in git, and make sure the commit message properly explains the reasoning behind the patch.

Do you intend this to go into LLVM, or are you still experimenting at this point? It may be best to make sure what you come up with will have practical use before making a lot of changes in llvm itself. My understanding is that this code is (overly) complex but it is the order it is for deliberate reasons. All the existing tests have to keep passing, if they are not already.

I would consider runtime unrolling to be the most interesting part of machine learning loop unroll factors, at least on many cpu's.

[WIP][NFC] Adding enum for unrolling option and adding MyDebug for priting

Solving the problems mentioned in the review

Adding NFC tag

Squashing all commits

[WIP] Reformatting using clang-reformat