Merge pull request #10803 from ethereum/shortcut-code-length

Implemented a shortcut  for ``address.code.length`` that generates ``…

Changelog.md

@@ -5,6 +5,7 @@ Language Features:
 
 Compiler Features:
  * Build system: Update the soljson.js build to emscripten 2.0.12 and boost 1.75.0.
+ * Code Generator: Reduce the cost of ``<address>.code.length`` by using ``extcodesize`` directly.
  * Command Line Interface: Allow "=" as separator between library name and address in ``--libraries`` commandline option.
  * Command Line Interface: New option ``--model-checker-targets`` allows specifying which targets should be checked. The valid options are ``all``, ``constantCondition``, ``underflow``, ``overflow``, ``divByZero``, ``balance``, ``assert``, ``popEmptyArray``, where the default is ``all``. Multiple targets can be chosen at the same time, separated by a comma without spaces: ``underflow,overflow,assert``.
  * Command Line Interface: Only accept the library address that is prefixed with "0x" in ``--libraries`` commandline option.

libsolidity/codegen/ExpressionCompiler.cpp

@@ -1473,6 +1473,29 @@ bool ExpressionCompiler::visit(MemberAccess const& _memberAccess)
 							return false;
 						}
 
+	// Another special case for `address.code.length`, which should simply call extcodesize
+	if (
+		auto innerExpression = dynamic_cast<MemberAccess const*>(&_memberAccess.expression());
+		member == "length" &&
+		innerExpression &&
+		innerExpression->memberName() == "code" &&
+		innerExpression->expression().annotation().type->category() == Type::Category::Address
+	)
+	{
+		solAssert(innerExpression->annotation().type->category() == Type::Category::Array, "");
+
+		innerExpression->expression().accept(*this);
+
+		utils().convertType(
+			*innerExpression->expression().annotation().type,
+			*TypeProvider::address(),
+			true
+		);
+		m_context << Instruction::EXTCODESIZE;
+
+		return false;
+	}
+
 	_memberAccess.expression().accept(*this);
 	switch (_memberAccess.expression().annotation().type->category())
 	{

libsolidity/codegen/ir/IRGeneratorForStatements.cpp

@@ -1554,6 +1554,28 @@ void IRGeneratorForStatements::endVisit(FunctionCallOptions const& _options)
 	}
 }
 
+bool IRGeneratorForStatements::visit(MemberAccess const& _memberAccess)
+{
+	// A shortcut for <address>.code.length. We skip visiting <address>.code and directly visit
+	// <address>. The actual code is generated in endVisit.
+	if (
+		auto innerExpression = dynamic_cast<MemberAccess const*>(&_memberAccess.expression());
+		_memberAccess.memberName() == "length" &&
+		innerExpression &&
+		innerExpression->memberName() == "code" &&
+		innerExpression->expression().annotation().type->category() == Type::Category::Address
+	)
+	{
+		solAssert(innerExpression->annotation().type->category() == Type::Category::Array, "");
+		// Skip visiting <address>.code
+		innerExpression->expression().accept(*this);
+
+		return false;
+	}
+
+	return true;
+}
+
 void IRGeneratorForStatements::endVisit(MemberAccess const& _memberAccess)
 {
 	setLocation(_memberAccess);
@@ -1846,13 +1868,26 @@ void IRGeneratorForStatements::endVisit(MemberAccess const& _memberAccess)
 	case Type::Category::Array:
 	{
 		auto const& type = dynamic_cast<ArrayType const&>(*_memberAccess.expression().annotation().type);
-
 		if (member == "length")
-			define(_memberAccess) <<
-				m_utils.arrayLengthFunction(type) <<
-				"(" <<
-				IRVariable(_memberAccess.expression()).commaSeparatedList() <<
-				")\n";
+		{
+			// shortcut for <address>.code.length
+			if (
+				auto innerExpression = dynamic_cast<MemberAccess const*>(&_memberAccess.expression());
+				innerExpression &&
+				innerExpression->memberName() == "code" &&
+				innerExpression->expression().annotation().type->category() == Type::Category::Address
+			)
+				define(_memberAccess) <<
+					"extcodesize(" <<
+					expressionAsType(innerExpression->expression(), *TypeProvider::address()) <<
+					")\n";
+			else
+				define(_memberAccess) <<
+					m_utils.arrayLengthFunction(type) <<
+					"(" <<
+					IRVariable(_memberAccess.expression()).commaSeparatedList() <<
+					")\n";
+		}
 		else if (member == "pop" || member == "push")
 		{
 			solAssert(type.location() == DataLocation::Storage, "");

libsolidity/codegen/ir/IRGeneratorForStatements.h

@@ -87,6 +87,7 @@ public:
 	bool visit(BinaryOperation const& _binOp) override;
 	void endVisit(FunctionCall const& _funCall) override;
 	void endVisit(FunctionCallOptions const& _funCallOptions) override;
+	bool visit(MemberAccess const& _memberAccess) override;
 	void endVisit(MemberAccess const& _memberAccess) override;
 	bool visit(InlineAssembly const& _inlineAsm) override;
 	void endVisit(IndexAccess const& _indexAccess) override;

test/libsolidity/semanticTests/various/code_length.sol

@@ -0,0 +1,64 @@
+// SPDX-License-Identifier: GPL-3.0
+contract C {
+    uint len1;
+    uint len2;
+    constructor() {
+        uint mem_ptr_before;
+        uint mem_ptr_after;
+
+        assembly {
+            mem_ptr_before := mload(64)
+        }
+
+        len1 = address(0).code.length;
+
+        assembly {
+            mem_ptr_after := mload(64)
+        }
+
+        // To check that no memory was allocated and written.
+        assert(mem_ptr_before == mem_ptr_after);
+
+        len2 = address(this).code.length;
+
+        // To check that no memory was allocated and written.
+        assembly {
+            mem_ptr_after := mload(64)
+        }
+
+        assert(mem_ptr_before == mem_ptr_after);
+
+    }
+
+    function f() public view returns (bool r1, bool r2) {
+        uint mem_ptr_before;
+        uint mem_ptr_after;
+
+        assembly {
+            mem_ptr_before := mload(64)
+        }
+
+        r1 = address(this).code.length > 50;
+
+        assembly {
+            mem_ptr_after := mload(64)
+        }
+
+        // To check that no memory was allocated and written.
+        assert(mem_ptr_before == mem_ptr_after);
+
+        address a = address(0);
+        r2 = a.code.length == 0;
+
+        // To check that no memory was allocated and written.
+        assembly {
+            mem_ptr_after := mload(64)
+        }
+
+    }
+}
+// ====
+// compileViaYul: also
+// ----
+// constructor()
+// f(): true, true -> true, true

test/libsolidity/semanticTests/various/code_length_contract_member.sol

@@ -0,0 +1,17 @@
+// Test to see if type.code.length does extcodesize(type) only when type is an address.
+struct S {
+    bytes32 code;
+    bytes32 another;
+}
+
+contract C {
+    S s;
+
+    function f() public returns (uint, uint, bool) {
+        return (s.code.length, s.another.length, address(this).code.length > 50);
+    }
+}
+// ====
+// compileViaYul: also
+// ----
+// f() -> 0x20, 0x20, true