In the bit tracker, references to other bit values in which the register
is 0 are prohibited. This means that generating self-referential register
cells like { w:32 [0-15]:s[0-15] [16-31]:s[15] } is impossible. In order
to get a self-referential cell, it had to be stored into a map and then
reloaded from it. To avoid this step, add a function that will set the
register to a given value without going through the map.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@296025 91177308-0d34-0410-b5e6-96231b3b80d8
c5dd216734