Fix for deleting byte array elements.

Fixes #1759.

libsolidity/LValue.cpp

@@ -311,8 +311,6 @@ void StorageByteArrayElement::retrieveValue(SourceLocation const&, bool _remove)
 
 void StorageByteArrayElement::storeValue(Type const&, SourceLocation const&, bool _move) const
 {
-	//@todo optimize this
-
 	// stack: value ref byte_number
 	m_context << u256(31) << eth::Instruction::SUB << u256(0x100) << eth::Instruction::EXP;
 	// stack: value ref (1<<(8*(31-byte_number)))
@@ -335,19 +333,16 @@ void StorageByteArrayElement::setToZero(SourceLocation const&, bool _removeRefer
 {
 	// stack: ref byte_number
 	if (!_removeReference)
-		m_context << eth::Instruction::SWAP1 << eth::Instruction::DUP2;
+		m_context << eth::Instruction::DUP2 << eth::Instruction::DUP2;
 	m_context << u256(31) << eth::Instruction::SUB << u256(0x100) << eth::Instruction::EXP;
 	// stack: ref (1<<(8*(31-byte_number)))
 	m_context << eth::Instruction::DUP2 << eth::Instruction::SLOAD;
 	// stack: ref (1<<(8*(31-byte_number))) old_full_value
 	// clear byte in old value
-	m_context << eth::Instruction::SWAP1 << u256(0xff) << eth::Instruction::MUL << eth::Instruction::AND;
+	m_context << eth::Instruction::SWAP1 << u256(0xff) << eth::Instruction::MUL;
+	m_context << eth::Instruction::NOT << eth::Instruction::AND;
 	// stack: ref old_full_value_with_cleared_byte
 	m_context << eth::Instruction::SWAP1 << eth::Instruction::SSTORE;
-	if (!_removeReference)
-		m_context << eth::Instruction::SWAP1;
-	else
-		m_context << eth::Instruction::POP;
 }
 
 StorageArrayLength::StorageArrayLength(CompilerContext& _compilerContext, const ArrayType& _arrayType):

test/libsolidity/SolidityEndToEndTest.cpp

@@ -3381,6 +3381,26 @@ BOOST_AUTO_TEST_CASE(bytes_index_access)
 	BOOST_CHECK(callContractFunction("storageWrite()") == encodeArgs(0x193));
 }
 
+BOOST_AUTO_TEST_CASE(bytes_delete_element)
+{
+	char const* sourceCode = R"(
+		contract c {
+			bytes data;
+			function test1() external returns (bool) {
+				data.length = 100;
+				for (uint i = 0; i < data.length; i++)
+					data[i] = byte(i);
+				delete data[94];
+				delete data[96];
+				delete data[98];
+				return data[94] == 0 && data[95] == 95 && data[96] == 0 && data[97] == 97;
+			}
+		}
+	)";
+	compileAndRun(sourceCode);
+	BOOST_CHECK(callContractFunction("test1()") == encodeArgs(true));
+}
+
 BOOST_AUTO_TEST_CASE(array_copy_calldata_storage)
 {
 	char const* sourceCode = R"(