From 037b97ef4a53c30f2800777a88d754a898bccc2b Mon Sep 17 00:00:00 2001
From: Alex Beregszaszi <alex@rtfs.hu>
Date: Thu, 4 Jan 2018 12:05:01 +0000
Subject: [PATCH 1/2] Replace MOD with AND if constant is power of 2

---
 libevmasm/RuleList.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/libevmasm/RuleList.h b/libevmasm/RuleList.h
index 2312d673c..da522cec8 100644
--- a/libevmasm/RuleList.h
+++ b/libevmasm/RuleList.h
@@ -153,6 +153,17 @@ std::vector<SimplificationRule<Pattern>> simplificationRuleList(
 		{{Instruction::OR, {{Instruction::NOT, {X}}, X}}, [=]{ return ~u256(0); }, true},
 	};
 
+	// Replace MOD X, <power-of-two> with AND X, <power-of-two> - 1
+	for (size_t i = 0; i < 256; ++i)
+	{
+		u256 value = u256(1) << i;
+		rules.push_back({
+			{Instruction::MOD, {X, value}},
+			[=]() -> Pattern { return {Instruction::AND, {X, value - 1}}; },
+			false
+		});
+	}
+
 	// Double negation of opcodes with boolean result
 	for (auto const& op: std::vector<Instruction>{
 		Instruction::EQ,

From 1e09d6ba7b7117d5139472cc2c4af6d7f3ae91e9 Mon Sep 17 00:00:00 2001
From: chriseth <chris@ethereum.org>
Date: Fri, 9 Feb 2018 19:00:16 +0100
Subject: [PATCH 2/2] Test for Mod-And rule.

---
 test/libjulia/Simplifier.cpp | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/test/libjulia/Simplifier.cpp b/test/libjulia/Simplifier.cpp
index b48d45c84..4d4e8d53a 100644
--- a/test/libjulia/Simplifier.cpp
+++ b/test/libjulia/Simplifier.cpp
@@ -127,4 +127,16 @@ BOOST_AUTO_TEST_CASE(inside_for)
 	);
 }
 
+BOOST_AUTO_TEST_CASE(mod_and)
+{
+	CHECK(
+		"{ mstore(0, mod(calldataload(0), exp(2, 8))) }",
+		"{ mstore(0, and(calldataload(0), 255)) }"
+	);
+	CHECK(
+		"{ mstore(0, mod(calldataload(0), exp(2, 255))) }",
+		"{ mstore(0, and(calldataload(0), 0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff)) }"
+	);
+}
+
 BOOST_AUTO_TEST_SUITE_END()