Merge pull request #3693 from ethereum/optimizeMLOAD

Optimize across MLOAD if MSIZE is not used.

3 files changed, 45 insertions, 25 deletions

diff --git a/libsolidity/ast/Types.h b/libsolidity/ast/Types.h
index b7e64891..2c392705 100644
--- a/libsolidity/ast/Types.h
+++ b/libsolidity/ast/Types.h
@@ -229,6 +229,9 @@ public:
 	/// i.e. it behaves differently in lvalue context and in value context.
 	virtual bool isValueType() const { return false; }
 	virtual unsigned sizeOnStack() const { return 1; }
+	/// If it is possible to initialize such a value in memory by just writing zeros
+	/// of the size memoryHeadSize().
+	virtual bool hasSimpleZeroValueInMemory() const { return true; }
 	/// @returns the mobile (in contrast to static) type corresponding to the given type.
 	/// This returns the corresponding IntegerType or FixedPointType for RationalNumberType
 	/// and the pointer type for storage reference types.
@@ -568,6 +571,7 @@ public:
 
 	virtual TypePointer mobileType() const override { return copyForLocation(m_location, true); }
 	virtual bool dataStoredIn(DataLocation _location) const override { return m_location == _location; }
+	virtual bool hasSimpleZeroValueInMemory() const override { return false; }
 
 	/// Storage references can be pointers or bound references. In general, local variables are of
 	/// pointer type, state variables are bound references. Assignments to pointers or deleting
@@ -855,6 +859,7 @@ public:
 	virtual u256 storageSize() const override;
 	virtual bool canLiveOutsideStorage() const override { return false; }
 	virtual unsigned sizeOnStack() const override;
+	virtual bool hasSimpleZeroValueInMemory() const override { return false; }
 	virtual TypePointer mobileType() const override;
 	/// Converts components to their temporary types and performs some wildcard matching.
 	virtual TypePointer closestTemporaryType(TypePointer const& _targetType) const override;
@@ -999,6 +1004,7 @@ public:
 	virtual bool isValueType() const override { return true; }
 	virtual bool canLiveOutsideStorage() const override { return m_kind == Kind::Internal || m_kind == Kind::External; }
 	virtual unsigned sizeOnStack() const override;
+	virtual bool hasSimpleZeroValueInMemory() const override { return false; }
 	virtual MemberList::MemberMap nativeMembers(ContractDefinition const* _currentScope) const override;
 	virtual TypePointer encodingType() const override;
 	virtual TypePointer interfaceType(bool _inLibrary) const override;
@@ -1104,6 +1110,8 @@ public:
 		return _inLibrary ? shared_from_this() : TypePointer();
 	}
 	virtual bool dataStoredIn(DataLocation _location) const override { return _location == DataLocation::Storage; }
+	/// Cannot be stored in memory, but just in case.
+	virtual bool hasSimpleZeroValueInMemory() const override { solAssert(false, ""); }
 
 	TypePointer const& keyType() const { return m_keyType; }
 	TypePointer const& valueType() const { return m_valueType; }
@@ -1132,6 +1140,7 @@ public:
 	virtual u256 storageSize() const override;
 	virtual bool canLiveOutsideStorage() const override { return false; }
 	virtual unsigned sizeOnStack() const override;
+	virtual bool hasSimpleZeroValueInMemory() const override { solAssert(false, ""); }
 	virtual std::string toString(bool _short) const override { return "type(" + m_actualType->toString(_short) + ")"; }
 	virtual MemberList::MemberMap nativeMembers(ContractDefinition const* _currentScope) const override;
 
@@ -1154,6 +1163,7 @@ public:
 	virtual u256 storageSize() const override;
 	virtual bool canLiveOutsideStorage() const override { return false; }
 	virtual unsigned sizeOnStack() const override { return 0; }
+	virtual bool hasSimpleZeroValueInMemory() const override { solAssert(false, ""); }
 	virtual std::string richIdentifier() const override;
 	virtual bool operator==(Type const& _other) const override;
 	virtual std::string toString(bool _short) const override;
@@ -1179,6 +1189,7 @@ public:
 	virtual bool operator==(Type const& _other) const override;
 	virtual bool canBeStored() const override { return false; }
 	virtual bool canLiveOutsideStorage() const override { return true; }
+	virtual bool hasSimpleZeroValueInMemory() const override { solAssert(false, ""); }
 	virtual unsigned sizeOnStack() const override { return 0; }
 	virtual MemberList::MemberMap nativeMembers(ContractDefinition const*) const override;
 
@@ -1209,6 +1220,7 @@ public:
 	virtual bool operator==(Type const& _other) const override;
 	virtual bool canBeStored() const override { return false; }
 	virtual bool canLiveOutsideStorage() const override { return true; }
+	virtual bool hasSimpleZeroValueInMemory() const override { solAssert(false, ""); }
 	virtual unsigned sizeOnStack() const override { return 0; }
 	virtual MemberList::MemberMap nativeMembers(ContractDefinition const*) const override;
 
@@ -1238,6 +1250,7 @@ public:
 	virtual bool canLiveOutsideStorage() const override { return false; }
 	virtual bool isValueType() const override { return true; }
 	virtual unsigned sizeOnStack() const override { return 1; }
+	virtual bool hasSimpleZeroValueInMemory() const override { solAssert(false, ""); }
 	virtual std::string toString(bool) const override { return "inaccessible dynamic type"; }
 	virtual TypePointer decodingType() const override { return std::make_shared<IntegerType>(256); }
 };
diff --git a/libsolidity/codegen/CompilerUtils.cpp b/libsolidity/codegen/CompilerUtils.cpp
index 676d5d4e..deaef017 100644
--- a/libsolidity/codegen/CompilerUtils.cpp
+++ b/libsolidity/codegen/CompilerUtils.cpp
@@ -495,14 +495,34 @@ void CompilerUtils::abiDecodeV2(TypePointers const& _parameterTypes, bool _fromM
 
 void CompilerUtils::zeroInitialiseMemoryArray(ArrayType const& _type)
 {
-	auto repeat = m_context.newTag();
-	m_context << repeat;
-	pushZeroValue(*_type.baseType());
-	storeInMemoryDynamic(*_type.baseType());
-	m_context << Instruction::SWAP1 << u256(1) << Instruction::SWAP1;
-	m_context << Instruction::SUB << Instruction::SWAP1;
-	m_context << Instruction::DUP2;
-	m_context.appendConditionalJumpTo(repeat);
+	if (_type.baseType()->hasSimpleZeroValueInMemory())
+	{
+		solAssert(_type.baseType()->isValueType(), "");
+		Whiskers templ(R"({
+			let size := mul(length, <element_size>)
+			// cheap way of zero-initializing a memory range
+			codecopy(memptr, codesize(), size)
+			memptr := add(memptr, size)
+		})");
+		templ("element_size", to_string(_type.baseType()->memoryHeadSize()));
+		m_context.appendInlineAssembly(templ.render(), {"length", "memptr"});
+	}
+	else
+	{
+		// TODO: Potential optimization:
+		// When we create a new multi-dimensional dynamic array, each element
+		// is initialized to an empty array. It actually does not hurt
+		// to re-use exactly the same empty array for all elements. Currently,
+		// a new one is created each time.
+		auto repeat = m_context.newTag();
+		m_context << repeat;
+		pushZeroValue(*_type.baseType());
+		storeInMemoryDynamic(*_type.baseType());
+		m_context << Instruction::SWAP1 << u256(1) << Instruction::SWAP1;
+		m_context << Instruction::SUB << Instruction::SWAP1;
+		m_context << Instruction::DUP2;
+		m_context.appendConditionalJumpTo(repeat);
+	}
 	m_context << Instruction::SWAP1 << Instruction::POP;
 }
 
diff --git a/libsolidity/codegen/ExpressionCompiler.cpp b/libsolidity/codegen/ExpressionCompiler.cpp
index 9e2d30d5..76aa6843 100644
--- a/libsolidity/codegen/ExpressionCompiler.cpp
+++ b/libsolidity/codegen/ExpressionCompiler.cpp
@@ -850,8 +850,6 @@ bool ExpressionCompiler::visit(FunctionCall const& _functionCall)
 		}
 		case FunctionType::Kind::ObjectCreation:
 		{
-			// Will allocate at the end of memory (MSIZE) and not write at all unless the base
-			// type is dynamically sized.
 			ArrayType const& arrayType = dynamic_cast<ArrayType const&>(*_functionCall.annotation().type);
 			_functionCall.expression().accept(*this);
 			solAssert(arguments.size() == 1, "");
@@ -861,15 +859,7 @@ bool ExpressionCompiler::visit(FunctionCall const& _functionCall)
 			utils().convertType(*arguments[0]->annotation().type, IntegerType(256));
 
 			// Stack: requested_length
-			// Allocate at max(MSIZE, freeMemoryPointer)
 			utils().fetchFreeMemoryPointer();
-			m_context << Instruction::DUP1 << Instruction::MSIZE;
-			m_context << Instruction::LT;
-			auto initialise = m_context.appendConditionalJump();
-			// Free memory pointer does not point to empty memory, use MSIZE.
-			m_context << Instruction::POP;
-			m_context << Instruction::MSIZE;
-			m_context << initialise;
 
 			// Stack: requested_length memptr
 			m_context << Instruction::SWAP1;
@@ -894,13 +884,10 @@ bool ExpressionCompiler::visit(FunctionCall const& _functionCall)
 			// Check if length is zero
 			m_context << Instruction::DUP1 << Instruction::ISZERO;
 			auto skipInit = m_context.appendConditionalJump();
-
-			// We only have to initialise if the base type is a not a value type.
-			if (dynamic_cast<ReferenceType const*>(arrayType.baseType().get()))
-			{
-				m_context << Instruction::DUP2 << u256(32) << Instruction::ADD;
-				utils().zeroInitialiseMemoryArray(arrayType);
-			}
+			// Always initialize because the free memory pointer might point at
+			// a dirty memory area.
+			m_context << Instruction::DUP2 << u256(32) << Instruction::ADD;
+			utils().zeroInitialiseMemoryArray(arrayType);
 			m_context << skipInit;
 			m_context << Instruction::POP;
 			break;