When XDEBUG is enabled, check for SelectionDAG cycles at some key

points.  This will help us find future problems like the one
described in PR6019.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94019 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/SelectionDAG.h

@@ -63,6 +63,10 @@ enum CombineLevel {
   NoIllegalOperations // Combine may only create legal operations and types.
 };
 
+class SelectionDAG;
+void checkForCycles(const SDNode *N);
+void checkForCycles(const SelectionDAG *DAG);
+
 /// SelectionDAG class - This is used to represent a portion of an LLVM function
 /// in a low-level Data Dependence DAG representation suitable for instruction
 /// selection.  This DAG is constructed as the first step of instruction
@@ -204,7 +208,12 @@ public:
   const SDValue &setRoot(SDValue N) {
     assert((!N.getNode() || N.getValueType() == MVT::Other) &&
            "DAG root value is not a chain!");
-    return Root = N;
+    if (N.getNode())
+      checkForCycles(N.getNode());
+    Root = N;
+    if (N.getNode())
+      checkForCycles(this);
+    return Root;
   }
 
   /// Combine - This iterates over the nodes in the SelectionDAG, folding

include/llvm/CodeGen/SelectionDAGNodes.h

@@ -44,6 +44,8 @@ template <typename T> struct DenseMapInfo;
 template <typename T> struct simplify_type;
 template <typename T> struct ilist_traits;
 
+void checkForCycles(const SDNode *N);
+  
 /// SDVTList - This represents a list of ValueType's that has been intern'd by
 /// a SelectionDAG.  Instances of this simple value class are returned by
 /// SelectionDAG::getVTList(...).
@@ -1363,6 +1365,7 @@ protected:
       OperandList[i].setUser(this);
       OperandList[i].setInitial(Ops[i]);
     }
+    checkForCycles(this);
   }
 
   /// This constructor adds no operands itself; operands can be
@@ -1379,6 +1382,7 @@ protected:
     Ops[0].setInitial(Op0);
     NumOperands = 1;
     OperandList = Ops;
+    checkForCycles(this);
   }
 
   /// InitOperands - Initialize the operands list of this with 2 operands.
@@ -1389,6 +1393,7 @@ protected:
     Ops[1].setInitial(Op1);
     NumOperands = 2;
     OperandList = Ops;
+    checkForCycles(this);
   }
 
   /// InitOperands - Initialize the operands list of this with 3 operands.
@@ -1402,6 +1407,7 @@ protected:
     Ops[2].setInitial(Op2);
     NumOperands = 3;
     OperandList = Ops;
+    checkForCycles(this);
   }
 
   /// InitOperands - Initialize the operands list of this with 4 operands.
@@ -1417,6 +1423,7 @@ protected:
     Ops[3].setInitial(Op3);
     NumOperands = 4;
     OperandList = Ops;
+    checkForCycles(this);
   }
 
   /// InitOperands - Initialize the operands list of this with N operands.
@@ -1427,6 +1434,7 @@ protected:
     }
     NumOperands = N;
     OperandList = Ops;
+    checkForCycles(this);
   }
 
   /// DropOperands - Release the operands and set this node to have