[SelectionDAG] Use KnownBits struct in DAG's computeKnownBits and simplifyDemandedBits

This patch replaces the separate APInts for KnownZero/KnownOne with a single KnownBits struct. This is similar to what was done to ValueTracking's version recently.

This is largely a mechanical transformation from KnownZero to Known.Zero.

Differential Revision: https://reviews.llvm.org/D32569

llvm-svn: 301620
diff --git a/llvm/lib/Target/Sparc/SparcISelLowering.h b/llvm/lib/Target/Sparc/SparcISelLowering.h
index 90d0398..cc6386b 100644
--- a/llvm/lib/Target/Sparc/SparcISelLowering.h
+++ b/llvm/lib/Target/Sparc/SparcISelLowering.h
@@ -66,8 +66,7 @@
     /// in Mask are known to be either zero or one and return them in the
     /// KnownZero/KnownOne bitsets.
     void computeKnownBitsForTargetNode(const SDValue Op,
-                                       APInt &KnownZero,
-                                       APInt &KnownOne,
+                                       KnownBits &Known,
                                        const APInt &DemandedElts,
                                        const SelectionDAG &DAG,
                                        unsigned Depth = 0) const override;