From 8fb9cfe141ea0ad6e8ec695273b2b8f901ea24c0 Mon Sep 17 00:00:00 2001
From: Adam Nemet <anemet@apple.com>
Date: Sat, 31 May 2014 16:23:20 +0000
Subject: [PATCH] [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
---
 include/llvm/CodeGen/SelectionDAG.h       |  2 +-
 include/llvm/CodeGen/SelectionDAGNodes.h  |  3 ++-
 lib/CodeGen/SelectionDAG/SelectionDAG.cpp | 27 +++++++++++++++--------
 3 files changed, 21 insertions(+), 11 deletions(-)

diff --git a/include/llvm/CodeGen/SelectionDAG.h b/include/llvm/CodeGen/SelectionDAG.h
index 66473554d03..c6d716a5355 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 f281a069706..09cac428418 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
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 0f1d9758348..b701add2de3 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -6002,6 +6002,8 @@ unsigned SelectionDAG::AssignTopologicalOrder() {
       SDNode *S = ++I;
       dbgs() << "Overran sorted position:\n";
       S->dumprFull(this); dbgs() << "\n";
+      dbgs() << "Checking if this is due to cycles\n";
+      checkForCycles(this, true);
 #endif
       llvm_unreachable(nullptr);
     }
@@ -6587,7 +6589,7 @@ bool ShuffleVectorSDNode::isSplatMask(const int *Mask, EVT VT) {
   return true;
 }
 
-#ifdef XDEBUG
+#ifndef NDEBUG
 static void checkForCyclesHelper(const SDNode *N,
                                  SmallPtrSet<const SDNode*, 32> &Visited,
                                  SmallPtrSet<const SDNode*, 32> &Checked,
@@ -6614,15 +6616,22 @@ static void checkForCyclesHelper(const SDNode *N,
 #endif
 
 void llvm::checkForCycles(const llvm::SDNode *N,
-                          const llvm::SelectionDAG *DAG) {
+                          const llvm::SelectionDAG *DAG,
+                          bool force) {
+#ifndef NDEBUG
+  bool check = force;
 #ifdef XDEBUG
-  assert(N && "Checking nonexistent SDNode");
-  SmallPtrSet<const SDNode*, 32> visited;
-  SmallPtrSet<const SDNode*, 32> checked;
-  checkForCyclesHelper(N, visited, checked, DAG);
-#endif
+  check = true;
+#endif  // XDEBUG
+  if (check) {
+    assert(N && "Checking nonexistent SDNode");
+    SmallPtrSet<const SDNode*, 32> visited;
+    SmallPtrSet<const SDNode*, 32> checked;
+    checkForCyclesHelper(N, visited, checked, DAG);
+  }
+#endif  // !NDEBUG
 }
 
-void llvm::checkForCycles(const llvm::SelectionDAG *DAG) {
-  checkForCycles(DAG->getRoot().getNode(), DAG);
+void llvm::checkForCycles(const llvm::SelectionDAG *DAG, bool force) {
+  checkForCycles(DAG->getRoot().getNode(), DAG, force);
 }
-- 
2.34.1