[llvm] Convert as many LivePhysRegs uses to LiveRegUnits (PR #83905)

[via llvm-commits]

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@@ -1036,15 +1036,27 @@ false:
 define void @stack_realign2(i32 %a, i32 %b, ptr %ptr1, ptr %ptr2, ptr %ptr3, ptr %ptr4, ptr %ptr5, ptr %ptr6) {
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ostannard wrote:

The comment above this function (which github won't let me comment on) is now out of date, it looks like we are now applying shrink-wrapping to this function. If this an expected result of this change?

https://github.com/llvm/llvm-project/pull/83905