GISel's CSE mechanism lazily inserts instructions into the CSE List
to improve on efficiency as well as efficacy of CSE
(for allowing partially built instructions to be fully built).
There's unfortunately a mutual recursion via
`handleRecordedInsts -> handleRecordedInst -> insertNode-> handleRecordedInsts`.
So this change simply records that we're already draining this list so we can just bail out on the recursion.
No changes to codegen are expected as we're still draining/handling the temporary
list via pop_back and we should get the same sequence of instructions
whether we call pop_back in a loop at the top level or recursive.
https://reviews.llvm.org/D145006
reviewed by: dsanders
00e55531df