Keep def-use-manager and inst-to-block mapping alive

Part of #1328.

We kill these two analyses a lot, and they are expensive to kill. Below is a table of the optimizations that kill them, and the work that needs to be done. "X" means we need to get that optimization to not kill that analysis, "D" means that it is done.

Optimization | def-use | inst-to-block
------------ | ------------- | -------------
merge-return | X | X
private-to-local | | D
local-single-store | | D
adce | | D
local-single-block | | D
ccp | D | D
dead-branch | | D
reduce-load-size | D | D
dead-insert | D | D
merge-block | D | D
compact-ids | | D