From: bdemsky <bdemsky@uci.edu>
Date: Wed, 12 Jun 2019 22:30:30 +0000 (-0700)
Subject: partial edits
X-Git-Url: http://plrg.eecs.uci.edu/git/?p=c11tester.git;a=commitdiff_plain;h=15162a2ac08b0a6b06e5319a7424055f4d12e01c

partial edits
---

diff --git a/clockvector.cc b/clockvector.cc
index 54e8c4a1..c86995bc 100644
--- a/clockvector.cc
+++ b/clockvector.cc
@@ -16,7 +16,7 @@
  * same thread or the parent that created this thread)
  * @param act is an action with which to update the ClockVector
  */
-ClockVector::ClockVector(ClockVector *parent, ModelAction *act)
+ClockVector::ClockVector(ClockVector *parent, const ModelAction *act)
 {
 	ASSERT(act);
 	num_threads = int_to_id(act->get_tid()) + 1;
diff --git a/clockvector.h b/clockvector.h
index 430dc177..962e9ec4 100644
--- a/clockvector.h
+++ b/clockvector.h
@@ -11,7 +11,7 @@
 
 class ClockVector {
 public:
-	ClockVector(ClockVector *parent = NULL, ModelAction *act = NULL);
+	ClockVector(ClockVector *parent = NULL, const ModelAction *act = NULL);
 	~ClockVector();
 	bool merge(const ClockVector *cv);
 	bool synchronized_since(const ModelAction *act) const;
diff --git a/cyclegraph.cc b/cyclegraph.cc
index 36f64a43..a3e86cf0 100644
--- a/cyclegraph.cc
+++ b/cyclegraph.cc
@@ -2,13 +2,11 @@
 #include "action.h"
 #include "common.h"
 #include "threads-model.h"
+#include "clockvector.h"
 
 /** Initializes a CycleGraph object. */
 CycleGraph::CycleGraph() :
-	discovered(new HashTable<const CycleNode *, const CycleNode *, uintptr_t, 4, model_malloc, model_calloc, model_free>(16)),
-	queue(new ModelVector<const CycleNode *>()),
-	hasCycles(false),
-	oldCycles(false)
+	queue(new SnapVector<const CycleNode *>())
 {
 }
 
@@ -16,7 +14,6 @@ CycleGraph::CycleGraph() :
 CycleGraph::~CycleGraph()
 {
 	delete queue;
-	delete discovered;
 }
 
 /**
@@ -62,51 +59,55 @@ CycleNode * CycleGraph::getNode(const ModelAction *action)
  * @param tonode The edge points to this CycleNode
  * @return True, if new edge(s) are added; otherwise false
  */
-bool CycleGraph::addNodeEdge(CycleNode *fromnode, CycleNode *tonode)
+void CycleGraph::addNodeEdge(CycleNode *fromnode, CycleNode *tonode)
 {
-	if (fromnode->addEdge(tonode)) {
-		rollbackvector.push_back(fromnode);
-		if (!hasCycles)
-			hasCycles = checkReachable(tonode, fromnode);
-	} else
-		return false;/* No new edge */
+	//quick check whether edge is redundant
+	if (checkReachable(fromnode, tonode))
+		return;
+
+	CycleNode *edgeSrcNode = fromnode;
 
 	/*
-	 * If the fromnode has a rmwnode that is not the tonode, we should
-	 * follow its RMW chain to add an edge at the end, unless we encounter
-	 * tonode along the way
+	 * If the fromnode has a rmwnode, we should
+	 * follow its RMW chain to add an edge at the end.
 	 */
 	CycleNode *rmwnode = fromnode->getRMW();
 	if (rmwnode) {
-		while (rmwnode != tonode && rmwnode->getRMW())
+		while (rmwnode->getRMW())
 			rmwnode = rmwnode->getRMW();
+		edgeSrcNode = rmwnode;
+	}
 
-		if (rmwnode != tonode) {
-			if (rmwnode->addEdge(tonode)) {
-				if (!hasCycles)
-					hasCycles = checkReachable(tonode, rmwnode);
-
-				rollbackvector.push_back(rmwnode);
+	edgeSrcNode->addEdge(tonode);	//Add edge to edgeSrcNode
+
+	/* Propagate clock vector changes */
+	if (tonode->cv->merge(edgeSrcNode->cv)) {
+		queue->push_back(edgeSrcNode);
+		while(!queue->empty()) {
+			const CycleNode *node = queue->back();
+			unsigned int numedges = node->getNumEdges();
+			for(unsigned int i = 0;i < numedges;i++) {
+				CycleNode * enode = node->getEdge(i);
+				if (enode->cv->merge(node->cv))
+					queue->push_back(enode);
 			}
 		}
 	}
-	return true;
 }
 
 /**
  * @brief Add an edge between a write and the RMW which reads from it
  *
  * Handles special case of a RMW action, where the ModelAction rmw reads from
- * the ModelAction/Promise from. The key differences are:
+ * the ModelAction from. The key differences are:
  *  -# No write can occur in between the @a rmw and @a from actions.
  *  -# Only one RMW action can read from a given write.
  *
- * @param from The edge comes from this ModelAction/Promise
+ * @param from The edge comes from this ModelAction
  * @param rmw The edge points to this ModelAction; this action must read from
- * the ModelAction/Promise from
+ * the ModelAction from
  */
-template <typename T>
-void CycleGraph::addRMWEdge(const T *from, const ModelAction *rmw)
+void CycleGraph::addRMWEdge(const ModelAction *from, const ModelAction *rmw)
 {
 	ASSERT(from);
 	ASSERT(rmw);
@@ -117,11 +118,7 @@ void CycleGraph::addRMWEdge(const T *from, const ModelAction *rmw)
 	/* We assume that this RMW has no RMW reading from it yet */
 	ASSERT(!rmwnode->getRMW());
 
-	/* Two RMW actions cannot read from the same write. */
-	if (fromnode->setRMW(rmwnode))
-		hasCycles = true;
-	else
-		rmwrollbackvector.push_back(fromnode);
+	fromnode->setRMW(rmwnode);
 
 	/* Transfer all outgoing edges from the from node to the rmw node */
 	/* This process should not add a cycle because either:
@@ -133,15 +130,12 @@ void CycleGraph::addRMWEdge(const T *from, const ModelAction *rmw)
 	for (unsigned int i = 0;i < fromnode->getNumEdges();i++) {
 		CycleNode *tonode = fromnode->getEdge(i);
 		if (tonode != rmwnode) {
-			if (rmwnode->addEdge(tonode))
-				rollbackvector.push_back(rmwnode);
+			rmwnode->addEdge(tonode);
 		}
 	}
 
 	addNodeEdge(fromnode, rmwnode);
 }
-/* Instantiate two forms of CycleGraph::addRMWEdge */
-template void CycleGraph::addRMWEdge(const ModelAction *from, const ModelAction *rmw);
 
 /**
  * @brief Adds an edge between objects
@@ -156,8 +150,8 @@ template void CycleGraph::addRMWEdge(const ModelAction *from, const ModelAction
  * @param from The edge comes from this object, of type U
  * @return True, if new edge(s) are added; otherwise false
  */
-template <typename T, typename U>
-bool CycleGraph::addEdge(const T *from, const U *to)
+
+void CycleGraph::addEdge(const ModelAction *from, const ModelAction *to)
 {
 	ASSERT(from);
 	ASSERT(to);
@@ -165,10 +159,8 @@ bool CycleGraph::addEdge(const T *from, const U *to)
 	CycleNode *fromnode = getNode(from);
 	CycleNode *tonode = getNode(to);
 
-	return addNodeEdge(fromnode, tonode);
+	addNodeEdge(fromnode, tonode);
 }
-/* Instantiate four forms of CycleGraph::addEdge */
-template bool CycleGraph::addEdge(const ModelAction *from, const ModelAction *to);
 
 #if SUPPORT_MOD_ORDER_DUMP
 
@@ -196,16 +188,13 @@ void CycleGraph::dot_print_node(FILE *file, const ModelAction *act)
 	print_node(file, getNode(act), 1);
 }
 
-template <typename T, typename U>
-void CycleGraph::dot_print_edge(FILE *file, const T *from, const U *to, const char *prop)
+void CycleGraph::dot_print_edge(FILE *file, const ModelAction *from, const ModelAction *to, const char *prop)
 {
 	CycleNode *fromnode = getNode(from);
 	CycleNode *tonode = getNode(to);
 
 	print_edge(file, fromnode, tonode, prop);
 }
-/* Instantiate two forms of CycleGraph::dot_print_edge */
-template void CycleGraph::dot_print_edge(FILE *file, const ModelAction *from, const ModelAction *to, const char *prop);
 
 void CycleGraph::dumpNodes(FILE *file) const
 {
@@ -240,34 +229,16 @@ void CycleGraph::dumpGraphToFile(const char *filename) const
  */
 bool CycleGraph::checkReachable(const CycleNode *from, const CycleNode *to) const
 {
-	discovered->reset();
-	queue->clear();
-	queue->push_back(from);
-	discovered->put(from, from);
-	while (!queue->empty()) {
-		const CycleNode *node = queue->back();
-		queue->pop_back();
-		if (node == to)
-			return true;
-		for (unsigned int i = 0;i < node->getNumEdges();i++) {
-			CycleNode *next = node->getEdge(i);
-			if (!discovered->contains(next)) {
-				discovered->put(next, next);
-				queue->push_back(next);
-			}
-		}
-	}
-	return false;
+	return to->cv->synchronized_since(from->action);
 }
 
 /**
- * Checks whether one ModelAction/Promise can reach another ModelAction/Promise
- * @param from The ModelAction or Promise from which to begin exploration
- * @param to The ModelAction or Promise to reach
+ * Checks whether one ModelAction can reach another ModelAction
+ * @param from The ModelAction from which to begin exploration
+ * @param to The ModelAction to reach
  * @return True, @a from can reach @a to; otherwise, false
  */
-template <typename T, typename U>
-bool CycleGraph::checkReachable(const T *from, const U *to) const
+bool CycleGraph::checkReachable(const ModelAction *from, const ModelAction *to) const
 {
 	CycleNode *fromnode = getNode_noCreate(from);
 	CycleNode *tonode = getNode_noCreate(to);
@@ -277,45 +248,6 @@ bool CycleGraph::checkReachable(const T *from, const U *to) const
 
 	return checkReachable(fromnode, tonode);
 }
-/* Instantiate four forms of CycleGraph::checkReachable */
-template bool CycleGraph::checkReachable(const ModelAction *from,
-																				 const ModelAction *to) const;
-
-/** @brief Begin a new sequence of graph additions which can be rolled back */
-void CycleGraph::startChanges()
-{
-	ASSERT(rollbackvector.empty());
-	ASSERT(rmwrollbackvector.empty());
-	ASSERT(oldCycles == hasCycles);
-}
-
-/** Commit changes to the cyclegraph. */
-void CycleGraph::commitChanges()
-{
-	rollbackvector.clear();
-	rmwrollbackvector.clear();
-	oldCycles = hasCycles;
-}
-
-/** Rollback changes to the previous commit. */
-void CycleGraph::rollbackChanges()
-{
-	for (unsigned int i = 0;i < rollbackvector.size();i++)
-		rollbackvector[i]->removeEdge();
-
-	for (unsigned int i = 0;i < rmwrollbackvector.size();i++)
-		rmwrollbackvector[i]->clearRMW();
-
-	hasCycles = oldCycles;
-	rollbackvector.clear();
-	rmwrollbackvector.clear();
-}
-
-/** @returns whether a CycleGraph contains cycles. */
-bool CycleGraph::checkForCycles() const
-{
-	return hasCycles;
-}
 
 /**
  * @brief Constructor for a CycleNode
@@ -323,7 +255,8 @@ bool CycleGraph::checkForCycles() const
  */
 CycleNode::CycleNode(const ModelAction *act) :
 	action(act),
-	hasRMW(NULL)
+	hasRMW(NULL),
+	cv(new ClockVector(NULL, act))
 {
 }
 
@@ -342,24 +275,6 @@ unsigned int CycleNode::getNumEdges() const
 	return edges.size();
 }
 
-/**
- * @brief Remove an element from a vector
- * @param v The vector
- * @param n The element to remove
- * @return True if the element was found; false otherwise
- */
-template <typename T>
-static bool vector_remove_node(SnapVector<T>& v, const T n)
-{
-	for (unsigned int i = 0;i < v.size();i++) {
-		if (v[i] == n) {
-			v.erase(v.begin() + i);
-			return true;
-		}
-	}
-	return false;
-}
-
 /**
  * @brief Remove a (forward) edge from this CycleNode
  * @return The CycleNode which was popped, if one exists; otherwise NULL
@@ -379,13 +294,12 @@ CycleNode * CycleNode::removeEdge()
  * @param node The node to which we add a directed edge
  * @return True if this edge is a new edge; false otherwise
  */
-bool CycleNode::addEdge(CycleNode *node)
+void CycleNode::addEdge(CycleNode *node)
 {
 	for (unsigned int i = 0;i < edges.size();i++)
 		if (edges[i] == node)
-			return false;
+			return;
 	edges.push_back(node);
-	return true;
 }
 
 /** @returns the RMW CycleNode that reads from the current CycleNode */
diff --git a/cyclegraph.h b/cyclegraph.h
index fefe3440..624ce885 100644
--- a/cyclegraph.h
+++ b/cyclegraph.h
@@ -23,58 +23,33 @@ class CycleGraph {
 public:
 	CycleGraph();
 	~CycleGraph();
+	void addEdge(const ModelAction *from, const ModelAction *to);
+	void addRMWEdge(const ModelAction *from, const ModelAction *rmw);
+	bool checkReachable(const ModelAction *from, const ModelAction *to) const;
 
-	template <typename T, typename U>
-	bool addEdge(const T *from, const U *to);
-
-	template <typename T>
-	void addRMWEdge(const T *from, const ModelAction *rmw);
-
-	bool checkForCycles() const;
-
-	template <typename T, typename U>
-	bool checkReachable(const T *from, const U *to) const;
-
-	void startChanges();
-	void commitChanges();
-	void rollbackChanges();
 #if SUPPORT_MOD_ORDER_DUMP
 	void dumpNodes(FILE *file) const;
 	void dumpGraphToFile(const char *filename) const;
-
 	void dot_print_node(FILE *file, const ModelAction *act);
-	template <typename T, typename U>
-	void dot_print_edge(FILE *file, const T *from, const U *to, const char *prop);
+	void dot_print_edge(FILE *file, const ModelAction *from, const ModelAction *to, const char *prop);
 #endif
-	CycleNode * getNode_noCreate(const ModelAction *act) const;
 
+	CycleNode * getNode_noCreate(const ModelAction *act) const;
 	SNAPSHOTALLOC
 private:
-	bool addNodeEdge(CycleNode *fromnode, CycleNode *tonode);
+	void addNodeEdge(CycleNode *fromnode, CycleNode *tonode);
 	void putNode(const ModelAction *act, CycleNode *node);
 	CycleNode * getNode(const ModelAction *act);
-	bool mergeNodes(CycleNode *node1, CycleNode *node2);
-
-	HashTable<const CycleNode *, const CycleNode *, uintptr_t, 4, model_malloc, model_calloc, model_free> *discovered;
-	ModelVector<const CycleNode *> * queue;
-
 
 	/** @brief A table for mapping ModelActions to CycleNodes */
 	HashTable<const ModelAction *, CycleNode *, uintptr_t, 4> actionToNode;
+	SnapVector<const CycleNode *> * queue;
 
 #if SUPPORT_MOD_ORDER_DUMP
 	SnapVector<CycleNode *> nodeList;
 #endif
 
 	bool checkReachable(const CycleNode *from, const CycleNode *to) const;
-
-	/** @brief A flag: true if this graph contains cycles */
-	bool hasCycles;
-	/** @brief The previous value of CycleGraph::hasCycles, for rollback */
-	bool oldCycles;
-
-	SnapVector<CycleNode *> rollbackvector;
-	SnapVector<CycleNode *> rmwrollbackvector;
 };
 
 /**
@@ -83,11 +58,10 @@ private:
 class CycleNode {
 public:
 	CycleNode(const ModelAction *act);
-	bool addEdge(CycleNode *node);
+	void addEdge(CycleNode *node);
 	CycleNode * getEdge(unsigned int i) const;
 	unsigned int getNumEdges() const;
 	CycleNode * removeEdge();
-
 	bool setRMW(CycleNode *);
 	CycleNode * getRMW() const;
 	void clearRMW() { hasRMW = NULL; }
@@ -104,6 +78,10 @@ private:
 	/** Pointer to a RMW node that reads from this node, or NULL, if none
 	 * exists */
 	CycleNode *hasRMW;
+
+	/** ClockVector for this Node. */
+	ClockVector *cv;
+	friend class CycleGraph;
 };
 
 #endif	/* __CYCLEGRAPH_H__ */
diff --git a/execution.cc b/execution.cc
index e253ab0f..b62f6944 100644
--- a/execution.cc
+++ b/execution.cc
@@ -28,7 +28,6 @@ struct model_snapshot_members {
 		used_sequence_numbers(0),
 		bugs(),
 		bad_synchronization(false),
-		bad_sc_read(false),
 		asserted(false)
 	{ }
 
@@ -43,16 +42,13 @@ struct model_snapshot_members {
 	SnapVector<bug_message *> bugs;
 	/** @brief Incorrectly-ordered synchronization was made */
 	bool bad_synchronization;
-	bool bad_sc_read;
 	bool asserted;
 
 	SNAPSHOTALLOC
 };
 
 /** @brief Constructor */
-ModelExecution::ModelExecution(ModelChecker *m,
-															 Scheduler *scheduler,
-															 NodeStack *node_stack) :
+ModelExecution::ModelExecution(ModelChecker *m, Scheduler *scheduler, NodeStack *node_stack) :
 	model(m),
 	params(NULL),
 	scheduler(scheduler),
@@ -190,13 +186,6 @@ void ModelExecution::set_bad_synchronization()
 	priv->bad_synchronization = true;
 }
 
-/** @brief Alert the model-checker that an incorrectly-ordered
- * synchronization was made */
-void ModelExecution::set_bad_sc_read()
-{
-	priv->bad_sc_read = true;
-}
-
 bool ModelExecution::assert_bug(const char *msg)
 {
 	priv->bugs.push_back(new bug_message(msg));
@@ -283,7 +272,7 @@ bool ModelExecution::is_complete_execution() const
  * @param rf_set is the set of model actions we can possibly read from
  * @return True if processing this read updates the mo_graph.
  */
-bool ModelExecution::process_read(ModelAction *curr, ModelVector<ModelAction *> * rf_set)
+bool ModelExecution::process_read(ModelAction *curr, SnapVector<ModelAction *> * rf_set)
 {
 	while(true) {
 
@@ -294,7 +283,7 @@ bool ModelExecution::process_read(ModelAction *curr, ModelVector<ModelAction *>
 		ASSERT(rf);
 
 		mo_graph->startChanges();
-		bool updated = r_modification_order(curr, rf);
+		r_modification_order(curr, rf);
 		if (!is_infeasible()) {
 			read_from(curr, rf);
 			mo_graph->commitChanges();
@@ -696,7 +685,7 @@ ModelAction * ModelExecution::check_current_action(ModelAction *curr)
 	if (!second_part_of_rmw)
 		add_action_to_lists(curr);
 
-	ModelVector<ModelAction *> * rf_set = NULL;
+	SnapVector<ModelAction *> * rf_set = NULL;
 	/* Build may_read_from set for newly-created actions */
 	if (newly_explored && curr->is_read())
 		rf_set = build_may_read_from(curr);
@@ -745,8 +734,6 @@ void ModelExecution::print_infeasibility(const char *prefix) const
 		ptr += sprintf(ptr, "[mo cycle]");
 	if (priv->bad_synchronization)
 		ptr += sprintf(ptr, "[bad sw ordering]");
-	if (priv->bad_sc_read)
-		ptr += sprintf(ptr, "[bad sc read]");
 	if (ptr != buf)
 		model_print("%s: %s", prefix ? prefix : "Infeasible", buf);
 }
@@ -760,8 +747,7 @@ void ModelExecution::print_infeasibility(const char *prefix) const
 bool ModelExecution::is_infeasible() const
 {
 	return mo_graph->checkForCycles() ||
-				 priv->bad_synchronization ||
-				 priv->bad_sc_read;
+				 priv->bad_synchronization;
 }
 
 /** Close out a RMWR by converting previous RMWR into a RMW or READ. */
@@ -791,12 +777,11 @@ ModelAction * ModelExecution::process_rmw(ModelAction *act) {
  * @param rf The ModelAction or Promise that curr reads from. Must be a write.
  * @return True if modification order edges were added; false otherwise
  */
-template <typename rf_type>
-bool ModelExecution::r_modification_order(ModelAction *curr, const rf_type *rf)
+
+bool ModelExecution::r_modification_order(ModelAction *curr, const ModelAction *rf, SnapVector<ModelAction *> * priorset)
 {
 	SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
 	unsigned int i;
-	bool added = false;
 	ASSERT(curr->is_read());
 
 	/* Last SC fence in the current thread */
@@ -838,20 +823,26 @@ bool ModelExecution::r_modification_order(ModelAction *curr, const rf_type *rf)
 				/* C++, Section 29.3 statement 5 */
 				if (curr->is_seqcst() && last_sc_fence_thread_local &&
 						*act < *last_sc_fence_thread_local) {
-					added = mo_graph->addEdge(act, rf) || added;
+				  if (mo_graph->checkReachable(rf, act))
+				    return false;
+				  priorset->add(act);
 					break;
 				}
 				/* C++, Section 29.3 statement 4 */
 				else if (act->is_seqcst() && last_sc_fence_local &&
 								 *act < *last_sc_fence_local) {
-					added = mo_graph->addEdge(act, rf) || added;
-					break;
+				  if (mo_graph->checkReachable(rf, act))
+				    return false;
+				  priorset->add(act);
+				  break;
 				}
 				/* C++, Section 29.3 statement 6 */
 				else if (last_sc_fence_thread_before &&
 								 *act < *last_sc_fence_thread_before) {
-					added = mo_graph->addEdge(act, rf) || added;
-					break;
+				  if (mo_graph->checkReachable(rf, act))
+				    return false;
+				  priorset->add(act);
+				  break;
 				}
 			}
 
@@ -861,18 +852,22 @@ bool ModelExecution::r_modification_order(ModelAction *curr, const rf_type *rf)
 			 */
 			if (act->happens_before(curr)) {
 				if (act->is_write()) {
-					added = mo_graph->addEdge(act, rf) || added;
+				  if (mo_graph->checkReachable(rf, act))
+				    return false;
+				  priorset->add(act);
 				} else {
 					const ModelAction *prevrf = act->get_reads_from();
-					if (!prevrf->equals(rf))
-						added = mo_graph->addEdge(prevrf, rf) || added;
+					if (!prevrf->equals(rf)) {
+					  if (mo_graph->checkReachable(rf, prevrf))
+					    return false;
+					  priorset->add(prevrf);
+					}
 				}
 				break;
 			}
 		}
 	}
-
-	return added;
+	return true;
 }
 
 /**
@@ -899,11 +894,10 @@ bool ModelExecution::r_modification_order(ModelAction *curr, const rf_type *rf)
  * value. If NULL, then don't record any future values.
  * @return True if modification order edges were added; false otherwise
  */
-bool ModelExecution::w_modification_order(ModelAction *curr)
+void ModelExecution::w_modification_order(ModelAction *curr)
 {
 	SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
 	unsigned int i;
-	bool added = false;
 	ASSERT(curr->is_write());
 
 	if (curr->is_seqcst()) {
@@ -911,7 +905,7 @@ bool ModelExecution::w_modification_order(ModelAction *curr)
 		         so we are initialized. */
 		ModelAction *last_seq_cst = get_last_seq_cst_write(curr);
 		if (last_seq_cst != NULL) {
-			added = mo_graph->addEdge(last_seq_cst, curr) || added;
+			mo_graph->addEdge(last_seq_cst, curr);
 		}
 	}
 
@@ -954,7 +948,7 @@ bool ModelExecution::w_modification_order(ModelAction *curr)
 			/* C++, Section 29.3 statement 7 */
 			if (last_sc_fence_thread_before && act->is_write() &&
 					*act < *last_sc_fence_thread_before) {
-				added = mo_graph->addEdge(act, curr) || added;
+				mo_graph->addEdge(act, curr);
 				break;
 			}
 
@@ -970,10 +964,10 @@ bool ModelExecution::w_modification_order(ModelAction *curr)
 				 *   readfrom(act) --mo--> act
 				 */
 				if (act->is_write())
-					added = mo_graph->addEdge(act, curr) || added;
+					mo_graph->addEdge(act, curr);
 				else if (act->is_read()) {
 					//if previous read accessed a null, just keep going
-					added = mo_graph->addEdge(act->get_reads_from(), curr) || added;
+					mo_graph->addEdge(act->get_reads_from(), curr);
 				}
 				break;
 			} else if (act->is_read() && !act->could_synchronize_with(curr) &&
@@ -994,8 +988,6 @@ bool ModelExecution::w_modification_order(ModelAction *curr)
 			}
 		}
 	}
-
-	return added;
 }
 
 /**
@@ -1327,7 +1319,7 @@ bool valequals(uint64_t val1, uint64_t val2, int size) {
  * @param curr is the current ModelAction that we are exploring; it must be a
  * 'read' operation.
  */
-ModelVector<ModelAction *> *  ModelExecution::build_may_read_from(ModelAction *curr)
+SnapVector<ModelAction *> *  ModelExecution::build_may_read_from(ModelAction *curr)
 {
 	SnapVector<action_list_t> *thrd_lists = obj_thrd_map.get(curr->get_location());
 	unsigned int i;
@@ -1338,7 +1330,8 @@ ModelVector<ModelAction *> *  ModelExecution::build_may_read_from(ModelAction *c
 	if (curr->is_seqcst())
 		last_sc_write = get_last_seq_cst_write(curr);
 
-	ModelVector<ModelAction *> * rf_set = new ModelVector<ModelAction *>();
+	SnapVector<ModelAction *> * rf_set = new SnapVector<ModelAction *>();
+	SnapVector<ModelAction *> * priorset = new SnapVector<ModelAction *>();
 
 	/* Iterate over all threads */
 	for (i = 0;i < thrd_lists->size();i++) {
diff --git a/execution.h b/execution.h
index 950d6335..40cd3ac0 100644
--- a/execution.h
+++ b/execution.h
@@ -120,7 +120,6 @@ private:
 
 	bool mo_may_allow(const ModelAction *writer, const ModelAction *reader);
 	void set_bad_synchronization();
-	void set_bad_sc_read();
 	bool should_wake_up(const ModelAction *curr, const Thread *thread) const;
 	void wake_up_sleeping_actions(ModelAction *curr);
 	modelclock_t get_next_seq_num();
@@ -128,7 +127,7 @@ private:
 	bool next_execution();
 	ModelAction * check_current_action(ModelAction *curr);
 	bool initialize_curr_action(ModelAction **curr);
-	bool process_read(ModelAction *curr, ModelVector<ModelAction *> * rf_set);
+	bool process_read(ModelAction *curr, SnapVector<ModelAction *> * rf_set);
 	bool process_write(ModelAction *curr);
 	bool process_fence(ModelAction *curr);
 	bool process_mutex(ModelAction *curr);
@@ -142,13 +141,11 @@ private:
 	ModelAction * get_last_seq_cst_write(ModelAction *curr) const;
 	ModelAction * get_last_seq_cst_fence(thread_id_t tid, const ModelAction *before_fence) const;
 	ModelAction * get_last_unlock(ModelAction *curr) const;
-	ModelVector<ModelAction *> * build_may_read_from(ModelAction *curr);
+	SnapVector<ModelAction *> * build_may_read_from(ModelAction *curr);
 	ModelAction * process_rmw(ModelAction *curr);
 
-	template <typename rf_type>
-	bool r_modification_order(ModelAction *curr, const rf_type *rf);
-
-	bool w_modification_order(ModelAction *curr);
+  bool r_modification_order(ModelAction *curr, const ModelAction *rf, SnapVector<ModelAction *> *priorset);
+	void w_modification_order(ModelAction *curr);
 	void get_release_seq_heads(ModelAction *acquire, ModelAction *read, rel_heads_list_t *release_heads);
 	bool release_seq_heads(const ModelAction *rf, rel_heads_list_t *release_heads) const;
 	ModelAction * get_uninitialized_action(const ModelAction *curr) const;
diff --git a/fuzzer.cc b/fuzzer.cc
index d3d9d2c5..9ad61c3c 100644
--- a/fuzzer.cc
+++ b/fuzzer.cc
@@ -3,7 +3,7 @@
 #include "threads-model.h"
 #include "model.h"
 
-int Fuzzer::selectWrite(ModelAction *read, ModelVector<ModelAction *> * rf_set) {
+int Fuzzer::selectWrite(ModelAction *read, SnapVector<ModelAction *> * rf_set) {
 	int random_index = random() % rf_set->size();
 	return random_index;
 }
diff --git a/fuzzer.h b/fuzzer.h
index 3a843510..6cf1efba 100644
--- a/fuzzer.h
+++ b/fuzzer.h
@@ -7,7 +7,7 @@
 class Fuzzer {
 public:
 	Fuzzer() {}
-	int selectWrite(ModelAction *read, ModelVector<ModelAction *>* rf_set);
+	int selectWrite(ModelAction *read, SnapVector<ModelAction *>* rf_set);
 	Thread * selectThread(Node *n, int * threadlist, int numthreads);
 	Thread * selectNotify(action_list_t * waiters);
 	MEMALLOC