[llvm] [Coroutines] Only rematerialize when operands are available after the suspend (PR #209195)

[via llvm-commits]

yoni-lavi wrote:

Net cost in frame size is `(bytes for all values introduced by doing the rematerialize - bytes for rematerialized value)`, we could decide to rematerialize if this net cost is negative.

alignment demands make this calculation more complicated though.

https://github.com/llvm/llvm-project/pull/209195