[llvm] Reland "[llvm][AArch64] Copy all operands when expanding BLR_BTI bundle (#78267)" (PR #78719)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

> Oh, I see, that makes more sense.
> 
> Is there some reason we can't just change the definition of BLR_BTI so it takes the same operands as BLR? Defining it to take different operands, then rewriting them to the form we want, seems like it's more complicated than necessary.

FWIW, 18.x gets branched on Tuesday, and I’d love to have this issue fixed there (not necessarily in the first RC, but at least by the first stable release). Does changing the definition of BLR_BTI make it less backportable (especially if the fix lands after the branch), rather than applying this fix first and looking into changing the definition later?

https://github.com/llvm/llvm-project/pull/78719