Merge pull request #2397 from ethereum/doublepush

Peephole optimizer for double push.

libevmasm/AssemblyItem.h

@@ -148,6 +148,14 @@ private:
 
 using AssemblyItems = std::vector<AssemblyItem>;
 
+inline size_t bytesRequired(AssemblyItems const& _items, size_t _addressLength)
+{
+	size_t size = 0;
+	for (AssemblyItem const& item: _items)
+		size += item.bytesRequired(_addressLength);
+	return size;
+}
+
 std::ostream& operator<<(std::ostream& _out, AssemblyItem const& _item);
 inline std::ostream& operator<<(std::ostream& _out, AssemblyItems const& _items)
 {

libevmasm/ConstantOptimiser.cpp

@@ -99,10 +99,7 @@ bigint ConstantOptimisationMethod::dataGas(bytes const& _data) const
 
 size_t ConstantOptimisationMethod::bytesRequired(AssemblyItems const& _items)
 {
-	size_t size = 0;
-	for (AssemblyItem const& item: _items)
-		size += item.bytesRequired(3); // assume 3 byte addresses
-	return size;
+	return eth::bytesRequired(_items, 3); // assume 3 byte addresses
 }
 
 void ConstantOptimisationMethod::replaceConstants(

libevmasm/PeepholeOptimiser.cpp

@@ -136,6 +136,21 @@ struct DoubleSwap: SimplePeepholeOptimizerMethod<DoubleSwap, 2>
 	}
 };
 
+struct DoublePush: SimplePeepholeOptimizerMethod<DoublePush, 2>
+{
+	static bool applySimple(AssemblyItem const& _push1, AssemblyItem const& _push2, std::back_insert_iterator<AssemblyItems> _out)
+	{
+		if (_push1.type() == Push && _push2.type() == Push && _push1.data() == _push2.data())
+		{
+			*_out = _push1;
+			*_out = {Instruction::DUP1, _push2.location()};
+			return true;
+		}
+		else
+			return false;
+	}
+};
+
 struct JumpToNext: SimplePeepholeOptimizerMethod<JumpToNext, 3>
 {
 	static size_t applySimple(
@@ -235,13 +250,15 @@ bool PeepholeOptimiser::optimise()
 {
 	OptimiserState state {m_items, 0, std::back_inserter(m_optimisedItems)};
 	while (state.i < m_items.size())
-		applyMethods(state, PushPop(), OpPop(), DoubleSwap(), JumpToNext(), UnreachableCode(), TagConjunctions(), Identity());
-	if (m_optimisedItems.size() < m_items.size())
+		applyMethods(state, PushPop(), OpPop(), DoublePush(), DoubleSwap(), JumpToNext(), UnreachableCode(), TagConjunctions(), Identity());
+	if (m_optimisedItems.size() < m_items.size() || (
+		m_optimisedItems.size() == m_items.size() &&
+		eth::bytesRequired(m_optimisedItems, 3) < eth::bytesRequired(m_items, 3)
+	))
 	{
 		m_items = std::move(m_optimisedItems);
 		return true;
 	}
 	else
 		return false;
-
 }