From 7c94e5462abb327016520b896178de41bea473c2 Mon Sep 17 00:00:00 2001
From: chriseth <chris@ethereum.org>
Date: Fri, 13 Oct 2017 18:59:04 +0200
Subject: [PATCH 1/2] Assume peephole optimizer was successful if number of
 pops increased.

---
 Changelog.md                    |  1 +
 libevmasm/Assembly.cpp          |  2 +-
 libevmasm/PeepholeOptimiser.cpp | 11 +++++++++--
 test/libevmasm/Optimiser.cpp    | 14 ++++++++++++++
 4 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/Changelog.md b/Changelog.md
index d78dbbba8..22b5c0027 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -13,6 +13,7 @@ Features:
  * Type Checker: Require ``storage`` or ``memory`` keyword for local variables as experimental 0.5.0 feature.
 
 Bugfixes:
+ * Optimizer: Remove unused stack computation results.
  * Parser: Fix source location of VariableDeclarationStatement.
  * Type Checker: Properly check array length and don't rely on an assertion in code generation.
  * Type Checker: Properly support overwriting members inherited from ``address`` in a contract
diff --git a/libevmasm/Assembly.cpp b/libevmasm/Assembly.cpp
index df691e7dd..37c4fb22d 100644
--- a/libevmasm/Assembly.cpp
+++ b/libevmasm/Assembly.cpp
@@ -407,7 +407,7 @@ map<u256, u256> Assembly::optimiseInternal(
 		if (_settings.runPeephole)
 		{
 			PeepholeOptimiser peepOpt(m_items);
-			while (peepOpt.optimise())
+			while (peepOpt.optimise() && count < 0xffffff)
 				count++;
 		}
 
diff --git a/libevmasm/PeepholeOptimiser.cpp b/libevmasm/PeepholeOptimiser.cpp
index 31fdd3176..168d11090 100644
--- a/libevmasm/PeepholeOptimiser.cpp
+++ b/libevmasm/PeepholeOptimiser.cpp
@@ -249,6 +249,11 @@ void applyMethods(OptimiserState& _state, Method, OtherMethods... _other)
 		applyMethods(_state, _other...);
 }
 
+size_t numberOfPops(AssemblyItems const& _items)
+{
+	return std::count(_items.begin(), _items.end(), Instruction::POP);
+}
+
 }
 
 bool PeepholeOptimiser::optimise()
@@ -257,8 +262,10 @@ bool PeepholeOptimiser::optimise()
 	while (state.i < 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_optimisedItems.size() == m_items.size() && (
+			eth::bytesRequired(m_optimisedItems, 3) < eth::bytesRequired(m_items, 3) ||
+			numberOfPops(m_optimisedItems) > numberOfPops(m_items)
+		)
 	))
 	{
 		m_items = std::move(m_optimisedItems);
diff --git a/test/libevmasm/Optimiser.cpp b/test/libevmasm/Optimiser.cpp
index 9dc495810..0ab95b080 100644
--- a/test/libevmasm/Optimiser.cpp
+++ b/test/libevmasm/Optimiser.cpp
@@ -841,6 +841,20 @@ BOOST_AUTO_TEST_CASE(peephole_double_push)
 	);
 }
 
+BOOST_AUTO_TEST_CASE(peephole_pop_calldatasize)
+{
+	AssemblyItems items{
+		u256(4),
+		Instruction::CALLDATASIZE,
+		Instruction::LT,
+		Instruction::POP
+	};
+	PeepholeOptimiser peepOpt(items);
+	for (size_t i = 0; i < 3; i++)
+		BOOST_CHECK(peepOpt.optimise());
+	BOOST_CHECK(items.empty());
+}
+
 BOOST_AUTO_TEST_CASE(jumpdest_removal)
 {
 	AssemblyItems items{

From f5e91e4a94b01daf2bbde637abef1796f063c348 Mon Sep 17 00:00:00 2001
From: chriseth <chris@ethereum.org>
Date: Mon, 16 Oct 2017 18:45:21 +0200
Subject: [PATCH 2/2] Throw on too many peephole optimizer iterations.

---
 libevmasm/Assembly.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/libevmasm/Assembly.cpp b/libevmasm/Assembly.cpp
index 37c4fb22d..5fab24e19 100644
--- a/libevmasm/Assembly.cpp
+++ b/libevmasm/Assembly.cpp
@@ -407,8 +407,11 @@ map<u256, u256> Assembly::optimiseInternal(
 		if (_settings.runPeephole)
 		{
 			PeepholeOptimiser peepOpt(m_items);
-			while (peepOpt.optimise() && count < 0xffffff)
+			while (peepOpt.optimise())
+			{
 				count++;
+				assertThrow(count < 64000, OptimizerException, "Peephole optimizer seems to be stuck.");
+			}
 		}
 
 		// This only modifies PushTags, we have to run again to actually remove code.