[SelectionDAG] Force cycle detection in AssignTopologicalOrder before aborting

DAG cycle detection is only enabled with ENABLE_EXPENSIVE_CHECKS.  However we
can run it just before we would crash in order to provide more informative
diagnostics.

Now in addition to the "Overran sorted position" message we also get the Node
printed if a cycle was detected.

Tested by building several configs: Debug+Assert, Debug+Assert+Check (this is
ENABLE_EXPENSIVE_CHECKS), Release+Assert and Release.  Also tried that the
AssignTopologicalOrder assert produces the expected results.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209977 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 3 insertions, 2 deletions

diff --git a/include/llvm/CodeGen/SelectionDAG.h b/include/llvm/CodeGen/SelectionDAG.h
index 66473554d0..c6d716a535 100644
--- a/include/llvm/CodeGen/SelectionDAG.h
+++ b/include/llvm/CodeGen/SelectionDAG.h
@@ -151,7 +151,7 @@ public:
 };
 
 class SelectionDAG;
-void checkForCycles(const SelectionDAG *DAG);
+void checkForCycles(const SelectionDAG *DAG, bool force = false);
 
 /// SelectionDAG class - This is used to represent a portion of an LLVM function
 /// in a low-level Data Dependence DAG representation suitable for instruction
diff --git a/include/llvm/CodeGen/SelectionDAGNodes.h b/include/llvm/CodeGen/SelectionDAGNodes.h
index f281a06970..09cac42841 100644
--- a/include/llvm/CodeGen/SelectionDAGNodes.h
+++ b/include/llvm/CodeGen/SelectionDAGNodes.h
@@ -49,7 +49,8 @@ template <typename T> struct DenseMapInfo;
 template <typename T> struct simplify_type;
 template <typename T> struct ilist_traits;
 
-void checkForCycles(const SDNode *N, const SelectionDAG *DAG = nullptr);
+void checkForCycles(const SDNode *N, const SelectionDAG *DAG = nullptr,
+                    bool force = false);
 
 /// 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