From 8047171a131779a6f1816339a0a380a51da7b548 Mon Sep 17 00:00:00 2001
From: Reuben Rodrigues <reubenrodrigues24@gmail.com>
Date: Thu, 8 Sep 2022 15:28:57 +0200
Subject: [PATCH] PeepholeOptimizer: StaticIfComparisons

---
 libevmasm/PeepholeOptimiser.cpp | 88 ++++++++++++++++++++++++++++++++-
 test/libevmasm/Optimiser.cpp    | 64 ++++++++++++++++++++++++
 2 files changed, 151 insertions(+), 1 deletion(-)

diff --git a/libevmasm/PeepholeOptimiser.cpp b/libevmasm/PeepholeOptimiser.cpp
index 334903c92..6efc849a9 100644
--- a/libevmasm/PeepholeOptimiser.cpp
+++ b/libevmasm/PeepholeOptimiser.cpp
@@ -428,6 +428,92 @@ struct TruthyAnd: SimplePeepholeOptimizerMethod<TruthyAnd>
 	}
 };
 
+// if(a == true) -> if (a)
+struct TruthyEqualComparison: SimplePeepholeOptimizerMethod<TruthyEqualComparison>{
+	static bool applySimple(
+		AssemblyItem const& _iszero,
+		AssemblyItem const& _iszero1,
+		AssemblyItem const& _push1,
+		AssemblyItem const& _eq,
+		std::back_insert_iterator<AssemblyItems>
+	)
+	{
+		if (
+			_iszero == Instruction::ISZERO &&
+			_iszero1 == Instruction::ISZERO &&
+			_push1.type() == Push && _push1.data() == 1 &&
+			_eq == Instruction::EQ
+		)
+		{
+			return true;
+		} else
+			return false;
+	}
+};
+
+// if(a != true) -> if(!a)
+struct TruthyInequalComparison: SimplePeepholeOptimizerMethod<TruthyInequalComparison>{
+	static bool applySimple(
+		AssemblyItem const& _iszero,
+		AssemblyItem const& _iszero1,
+		AssemblyItem const& _push1,
+		AssemblyItem const& _sub,
+		AssemblyItem const& _pushTag,
+		AssemblyItem const& _jumpi,
+		std::back_insert_iterator<AssemblyItems> _out
+	)
+	{
+		if (
+			_iszero == Instruction::ISZERO &&
+			_iszero1 == Instruction::ISZERO &&
+			_push1.type() == Push && _push1.data() == 1 &&
+			_sub == Instruction::SUB &&
+			_pushTag.type() == PushTag &&
+			_jumpi == Instruction::JUMPI
+		)
+		{
+			*_out = _iszero;
+			*_out = _pushTag;
+			*_out = _jumpi;
+			return true;
+		} else
+			return false;
+	}
+};
+
+// if(true != a) -> if(!a)
+struct ReverseTruthyInequalComparison: SimplePeepholeOptimizerMethod<ReverseTruthyInequalComparison>{
+	static bool applySimple(
+		AssemblyItem const& _push1,
+		AssemblyItem const& _swap1,
+		AssemblyItem const& _iszero,
+		AssemblyItem const& _iszero1,
+		AssemblyItem const& _sub,
+		AssemblyItem const& _pushTag,
+		AssemblyItem const& _jumpi,
+		std::back_insert_iterator<AssemblyItems> _out
+	)
+	{
+		if (
+			_push1.type() == Push && _push1.data() == 1 &&
+			SemanticInformation::isSwapInstruction(_swap1) &&
+			getSwapNumber(_swap1.instruction()) == 1 &&
+			_iszero == Instruction::ISZERO &&
+			_iszero1 == Instruction::ISZERO &&
+			_sub == Instruction::SUB &&
+			_pushTag.type() == PushTag &&
+			_jumpi == Instruction::JUMPI
+		)
+		{
+			*_out = _iszero;
+			*_out = _pushTag;
+			*_out = _jumpi;
+			return true;
+		} else
+			return false;
+	}
+};
+
 /// Removes everything after a JUMP (or similar) until the next JUMPDEST.
 struct UnreachableCode
 {
@@ -488,7 +574,7 @@ bool PeepholeOptimiser::optimise()
 	while (state.i < m_items.size())
 		applyMethods(
 			state,
-			PushPop(), OpPop(), OpStop(), OpReturnRevert(), DoublePush(), DoubleSwap(), CommutativeSwap(), SwapComparison(),
+			TruthyEqualComparison(), TruthyInequalComparison(), ReverseTruthyInequalComparison(), PushPop(), OpPop(), OpStop(), OpReturnRevert(), DoublePush(), DoubleSwap(), CommutativeSwap(), SwapComparison(),
 			DupSwap(), IsZeroIsZeroJumpI(), EqIsZeroJumpI(), DoubleJump(), JumpToNext(), UnreachableCode(),
 			TagConjunctions(), TruthyAnd(), Identity()
 		);
diff --git a/test/libevmasm/Optimiser.cpp b/test/libevmasm/Optimiser.cpp
index 6fc3c5a74..e98ab6acf 100644
--- a/test/libevmasm/Optimiser.cpp
+++ b/test/libevmasm/Optimiser.cpp
@@ -975,6 +975,70 @@ BOOST_AUTO_TEST_CASE(block_deduplicator_loops)
 	BOOST_CHECK_EQUAL(pushTags.size(), 1);
 }
 
+BOOST_AUTO_TEST_CASE(peephole_truthy_equal_comparison)
+{
+	AssemblyItems items{
+		Instruction::ISZERO,
+		Instruction::ISZERO,
+		AssemblyItem(Push, 1),
+		Instruction::EQ,
+	};
+	AssemblyItems expectation{};
+	PeepholeOptimiser peepOpt(items);
+	BOOST_REQUIRE(peepOpt.optimise());
+	BOOST_CHECK_EQUAL_COLLECTIONS(
+		items.begin(), items.end(),
+		expectation.begin(), expectation.end()
+	);
+}
+
+BOOST_AUTO_TEST_CASE(peephole_truthy_inequal_comparison)
+{
+	AssemblyItems items{
+		Instruction::ISZERO,
+		Instruction::ISZERO,
+		AssemblyItem(Push, 1),
+		Instruction::SUB,
+		AssemblyItem(PushTag, 1),
+		Instruction::JUMPI
+	};
+	AssemblyItems expectation{
+		Instruction::ISZERO,
+		AssemblyItem(PushTag, 1),
+		Instruction::JUMPI
+	};
+	PeepholeOptimiser peepOpt(items);
+	BOOST_REQUIRE(peepOpt.optimise());
+	BOOST_CHECK_EQUAL_COLLECTIONS(
+		items.begin(), items.end(),
+		expectation.begin(), expectation.end()
+	);
+}
+
+BOOST_AUTO_TEST_CASE(peephole_reverse_truthy_inequal_comparison)
+{
+	AssemblyItems items{
+		AssemblyItem(Push, 1),
+		Instruction::SWAP1,
+		Instruction::ISZERO,
+		Instruction::ISZERO,
+		Instruction::SUB,
+		AssemblyItem(PushTag, 1),
+		Instruction::JUMPI
+	};
+	AssemblyItems expectation{
+		Instruction::ISZERO,
+		AssemblyItem(PushTag, 1),
+		Instruction::JUMPI
+	};
+	PeepholeOptimiser peepOpt(items);
+	BOOST_REQUIRE(peepOpt.optimise());
+	BOOST_CHECK_EQUAL_COLLECTIONS(
+		items.begin(), items.end(),
+		expectation.begin(), expectation.end()
+	);
+}
+
 BOOST_AUTO_TEST_CASE(clear_unreachable_code)
 {
 	AssemblyItems items{