From ebfe7391ffdee815390185df28275a3e3c6ae9e3 Mon Sep 17 00:00:00 2001
From: chriseth <chris@ethereum.org>
Date: Mon, 14 Oct 2019 06:25:42 +0200
Subject: [PATCH] Use selfbalance for ``address(this).balance``.

---
 Changelog.md                                  |  1 +
 libsolidity/codegen/ExpressionCompiler.cpp    | 22 +++++++++++++++++++
 .../SolidityExpressionCompiler.cpp            | 19 ++++++++++++++++
 3 files changed, 42 insertions(+)

diff --git a/Changelog.md b/Changelog.md
index 22f845070..e4baf02db 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -4,6 +4,7 @@ Language Features:
 
 
 Compiler Features:
+ * Code Generator: Use SELFBALANCE for ``address(this).balance`` if using Istanbul EVM
 
 
 Bugfixes:
diff --git a/libsolidity/codegen/ExpressionCompiler.cpp b/libsolidity/codegen/ExpressionCompiler.cpp
index 2f8bf9455..ae740a6de 100644
--- a/libsolidity/codegen/ExpressionCompiler.cpp
+++ b/libsolidity/codegen/ExpressionCompiler.cpp
@@ -1229,6 +1229,28 @@ bool ExpressionCompiler::visit(MemberAccess const& _memberAccess)
 						utils().leftShiftNumberOnStack(224);
 						return false;
 					}
+	// Another special case for `address(this).balance`. Post-Istanbul, we can use the selfbalance
+	// opcode.
+	if (
+		m_context.evmVersion().hasSelfBalance() &&
+		member == "balance" &&
+		_memberAccess.expression().annotation().type->category() == Type::Category::Address
+	)
+		if (FunctionCall const* funCall = dynamic_cast<FunctionCall const*>(&_memberAccess.expression()))
+			if (auto const* addr = dynamic_cast<ElementaryTypeNameExpression const*>(&funCall->expression()))
+				if (
+					addr->typeName().token() == Token::Address &&
+					funCall->arguments().size() == 1
+				)
+					if (auto arg = dynamic_cast<Identifier const*>( funCall->arguments().front().get()))
+						if (
+							arg->name() == "this" &&
+							dynamic_cast<MagicVariableDeclaration const*>(arg->annotation().referencedDeclaration)
+						)
+						{
+							m_context << Instruction::SELFBALANCE;
+							return false;
+						}
 
 	_memberAccess.expression().accept(*this);
 	switch (_memberAccess.expression().annotation().type->category())
diff --git a/test/libsolidity/SolidityExpressionCompiler.cpp b/test/libsolidity/SolidityExpressionCompiler.cpp
index 607706162..551596456 100644
--- a/test/libsolidity/SolidityExpressionCompiler.cpp
+++ b/test/libsolidity/SolidityExpressionCompiler.cpp
@@ -617,6 +617,25 @@ BOOST_AUTO_TEST_CASE(gas_left)
 	BOOST_CHECK_EQUAL_COLLECTIONS(code.begin(), code.end(), expectation.begin(), expectation.end());
 }
 
+BOOST_AUTO_TEST_CASE(selfbalance)
+{
+	char const* sourceCode = R"(
+		contract test {
+			function f() returns (uint) {
+				return address(this).balance;
+			}
+		}
+	)";
+
+	bytes code = compileFirstExpression(sourceCode, {}, {});
+
+	if (dev::test::Options::get().evmVersion() == EVMVersion::istanbul())
+	{
+		bytes expectation({uint8_t(Instruction::SELFBALANCE)});
+		BOOST_CHECK_EQUAL_COLLECTIONS(code.begin(), code.end(), expectation.begin(), expectation.end());
+	}
+}
+
 BOOST_AUTO_TEST_SUITE_END()
 
 }