Introduce an option to rematerialize derived pointers immediately
before their uses instead of after every statepoint. This can be
beneficial when pointer is live across many statepoints but has
few uses.
Initial implementation is simple and rematerializes derived pointer
before every use, even if there are several uses in the same block
or rematerialization instructions can be hoisted etc.
Transformation is considered profitable if we would insert less
instructions than we would insert after every live statepoint.
Depends on D138910, D138911
Reviewed By: anna, skatkov
Differential Revision: https://reviews.llvm.org/D138912
86ed0daae7