From 93ebaa4822571cd0a83906b4665f34c34d2343f7 Mon Sep 17 00:00:00 2001
From: chriseth <c@ethdev.com>
Date: Fri, 29 Jul 2016 11:47:26 +0200
Subject: [PATCH] Reset knowledge in optimizer for path joins.

---
 libevmasm/Assembly.cpp         | 3 ++-
 libevmasm/ControlFlowGraph.cpp | 5 ++++-
 libevmasm/ControlFlowGraph.h   | 7 ++++++-
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/libevmasm/Assembly.cpp b/libevmasm/Assembly.cpp
index 7f7e1b9c3..2024b1e91 100644
--- a/libevmasm/Assembly.cpp
+++ b/libevmasm/Assembly.cpp
@@ -322,7 +322,8 @@ Assembly& Assembly::optimise(bool _enable, bool _isCreation, size_t _runs)
 			count++;
 
 		{
-			ControlFlowGraph cfg(m_items);
+			// Control flow graph that resets knowledge at path joins.
+			ControlFlowGraph cfg(m_items, false);
 			AssemblyItems optimisedItems;
 			for (BasicBlock const& block: cfg.optimisedBlocks())
 			{
diff --git a/libevmasm/ControlFlowGraph.cpp b/libevmasm/ControlFlowGraph.cpp
index fc2144c74..61b24e4b6 100644
--- a/libevmasm/ControlFlowGraph.cpp
+++ b/libevmasm/ControlFlowGraph.cpp
@@ -250,7 +250,10 @@ void ControlFlowGraph::gatherKnowledge()
 		KnownStatePointer state = item.state;
 		if (block.startState)
 		{
-			state->reduceToCommonKnowledge(*block.startState, !item.blocksSeen.count(item.blockId));
+			if (m_joinKnowledge)
+				state->reduceToCommonKnowledge(*block.startState, !item.blocksSeen.count(item.blockId));
+			else
+				state->reset();
 			if (*state == *block.startState)
 				continue;
 		}
diff --git a/libevmasm/ControlFlowGraph.h b/libevmasm/ControlFlowGraph.h
index 4480ba491..a6a9df8e0 100644
--- a/libevmasm/ControlFlowGraph.h
+++ b/libevmasm/ControlFlowGraph.h
@@ -94,7 +94,11 @@ class ControlFlowGraph
 public:
 	/// Initializes the control flow graph.
 	/// @a _items has to persist across the usage of this class.
-	ControlFlowGraph(AssemblyItems const& _items): m_items(_items) {}
+	/// @a _joinKnowledge if true, reduces state knowledge to common base at the join of two paths
+	explicit ControlFlowGraph(AssemblyItems const& _items, bool _joinKnowledge = true):
+		m_items(_items),
+		m_joinKnowledge(_joinKnowledge)
+	{}
 	/// @returns vector of basic blocks in the order they should be used in the final code.
 	/// Should be called only once.
 	BasicBlocks optimisedBlocks();
@@ -112,6 +116,7 @@ private:
 
 	unsigned m_lastUsedId = 0;
 	AssemblyItems const& m_items;
+	bool m_joinKnowledge;
 	std::map<BlockId, BasicBlock> m_blocks;
 };