[MIR] Support save/restore points with independent sets of registers (#119358)

This patch adds the MIR parsing and serialization support for save and
restore points with subsets of callee saved registers. That is, it
syntactically allows a function to contain two or more distinct
sub-regions in which distinct subsets of registers are spilled/filled as
callee save. This is useful if e.g. one of the CSRs isn't modified in
one of the sub-regions, but is in the other(s).

Support for actually using this capability in code generation is still
forthcoming. This patch is the next logical step for multiple
save/restore points support.

All points are now stored in DenseMap from MBB to vector of
CalleeSavedInfo.

Shrink-Wrap points split Part 4.
RFC:
https://discourse.llvm.org/t/shrink-wrap-save-restore-points-splitting/83581

Part 1: https://github.com/llvm/llvm-project/pull/117862 (landed)
Part 2: https://github.com/llvm/llvm-project/pull/119355 (landed)
Part 3: https://github.com/llvm/llvm-project/pull/119357 (landed)
Part 5: https://github.com/llvm/llvm-project/pull/119359 (likely to be
further split)

0 files changed, 0 insertions, 0 deletions