Routines for liveness in SSA trees.
Copyright (C) 2003-2024 Free Software Foundation, Inc.
Contributed by Andrew MacLeod <amacleod@redhat.com>
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Used to create the variable mapping when we go out of SSA form.
Mapping from an ssa_name to a partition number is maintained, as well as
partition number back to ssa_name.
This data structure also supports "views", which work on a subset of all
partitions. This allows the coalescer to decide what partitions are
interesting to it, and only work with those partitions. Whenever the view
is changed, the partition numbers change, but none of the partition groupings
change. (ie, it is truly a view since it doesn't change anything)
The final component of the data structure is the basevar map. This provides
a list of all the different base variables which occur in a partition view,
and a unique index for each one. Routines are provided to quickly produce
the base variable of a partition.
Note that members of a partition MUST all have the same base variable.
