Reorder (shl (add/sub (shl x, C0), y), C1) -> (add/sub (shl x, C0 + C1), (shl y, C1))

This is just expanding the existing pattern that exists for AND/XOR/OR
and gets a bit more parallelism in from the instruction sequence.

Alive2:
Add  - https://alive2.llvm.org/ce/z/dSmPkV
Sub1 - https://alive2.llvm.org/ce/z/6rpi5V
Sub2 - https://alive2.llvm.org/ce/z/UfYeUd

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D141875