Index: include/llvm/CodeGen/SelectionDAG.h
===================================================================
--- include/llvm/CodeGen/SelectionDAG.h
+++ include/llvm/CodeGen/SelectionDAG.h
@@ -388,7 +388,11 @@
     Node->OperandList = nullptr;
   }
   void CreateTopologicalOrder(std::vector<SDNode*>& Order);
+
 public:
+  // Maximum depth for DAG recursion, used by computeKnownBits etc.
+  static constexpr unsigned MaxRecursionDepth = 6;
+
   explicit SelectionDAG(const TargetMachine &TM, CodeGenOpt::Level);
   SelectionDAG(const SelectionDAG &) = delete;
   SelectionDAG &operator=(const SelectionDAG &) = delete;
Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -806,7 +806,7 @@
     return 0;
 
   // Don't recurse exponentially.
-  if (Depth > 6)
+  if (Depth > SelectionDAG::MaxRecursionDepth)
     return 0;
 
   switch (Op.getOpcode()) {
@@ -913,7 +913,8 @@
   if (Op.getOpcode() == ISD::FNEG)
     return Op.getOperand(0);
 
-  assert(Depth <= 6 && "GetNegatedExpression doesn't match isNegatibleForFree");
+  assert(Depth <= SelectionDAG::MaxRecursionDepth &&
+         "GetNegatedExpression doesn't match isNegatibleForFree");
   const TargetOptions &Options = DAG.getTarget().Options;
   const SDNodeFlags Flags = Op->getFlags();
 
Index: lib/CodeGen/SelectionDAG/SelectionDAG.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2422,7 +2422,7 @@
     return Known;
   }
 
-  if (Depth >= 6)
+  if (Depth >= MaxRecursionDepth)
     return Known;  // Limit search depth.
 
   KnownBits Known2;
@@ -3412,7 +3412,7 @@
     return Val.getNumSignBits();
   }
 
-  if (Depth >= 6)
+  if (Depth >= MaxRecursionDepth)
     return 1;  // Limit search depth.
 
   if (!DemandedElts)
@@ -3973,7 +3973,7 @@
   if (getTarget().Options.NoNaNsFPMath || Op->getFlags().hasNoNaNs())
     return true;
 
-  if (Depth >= 6)
+  if (Depth >= MaxRecursionDepth)
     return false; // Limit search depth.
 
   // TODO: Handle vectors.
Index: lib/CodeGen/SelectionDAG/TargetLowering.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -585,7 +585,7 @@
     SDValue Op, const APInt &DemandedBits, const APInt &DemandedElts,
     SelectionDAG &DAG, unsigned Depth) const {
   // Limit search depth.
-  if (Depth >= 6)
+  if (Depth >= SelectionDAG::MaxRecursionDepth)
     return SDValue();
 
   // Ignore UNDEFs.
@@ -798,7 +798,8 @@
   } else if (OriginalDemandedBits == 0 || OriginalDemandedElts == 0) {
     // Not demanding any bits/elts from Op.
     return TLO.CombineTo(Op, TLO.DAG.getUNDEF(VT));
-  } else if (Depth >= 6) { // Limit search depth.
+  } else if (Depth >= SelectionDAG::MaxRecursionDepth) {
+    // Limit search depth.
     return false;
   }
 
@@ -2107,7 +2108,7 @@
   }
 
   // Limit search depth.
-  if (Depth >= 6)
+  if (Depth >= SelectionDAG::MaxRecursionDepth)
     return false;
 
   SDLoc DL(Op);
Index: lib/Target/AArch64/AArch64ISelDAGToDAG.cpp
===================================================================
--- lib/Target/AArch64/AArch64ISelDAGToDAG.cpp
+++ lib/Target/AArch64/AArch64ISelDAGToDAG.cpp
@@ -2053,7 +2053,7 @@
 }
 
 static void getUsefulBits(SDValue Op, APInt &UsefulBits, unsigned Depth) {
-  if (Depth >= 6)
+  if (Depth >= SelectionDAG::MaxRecursionDepth)
     return;
   // Initialize UsefulBits
   if (!Depth) {