[llvm] [CodeGen] Preserve LiveStack analysis in StackSlotColoring pass (PR #94967)

[Vikash Gupta via llvm-commits]

vg0204 wrote:

This implementation is not as straightforward as it seems, as my current solution does not cover lot of corner cases. Also, I found that eventhough not stack slot re-usage may occur but stack slot coloring effectively re-assigns stack slots, which is currently like any change not updated in live stack. As a result, for example if a piece of code has 100 Stack slots objects all of which are just being re-assigned to new SS index supposedly (with no SS index sharing possible), this has to be propagated in LS results, which I feel is equivalent to creating entire new LS. Besides if there occur stack slot share, those all need to collected (could be any number), join their live ranges as well map them to newly assigned stack slot index, as it is very possible that all stack slots being shared themselves might get SS index re-assigned.

https://github.com/llvm/llvm-project/pull/94967