Not only is it useless, it's wrong: it doesn't check the correct operands.
(See ARMTargetLowering::computeKnownBitsForTargetNode for the other implementation.)
Fixes https://bugs.llvm.org//show_bug.cgi?id=32379 .
Looks even better than Pirama's patch. Thanks!
sidenote: I know I added *one* of these... now I'm wondering if I added the correct or broken one and how there ended up being two!
The correctness fix was already merged; I'll submit the cleanup separately.