Add configurable weights to CodeSize metric

libyul/optimiser/Metrics.cpp

@@ -36,30 +36,71 @@ using namespace solidity;
 using namespace solidity::yul;
 using namespace solidity::util;
 
-size_t CodeSize::codeSize(Statement const& _statement)
+size_t CodeWeights::costOf(Statement const& _statement) const
 {
-	CodeSize cs;
+	if (holds_alternative<ExpressionStatement>(_statement))
+		return expressionStatementCost;
+	else if (holds_alternative<Assignment>(_statement))
+		return assignmentCost;
+	else if (holds_alternative<VariableDeclaration>(_statement))
+		return variableDeclarationCost;
+	else if (holds_alternative<FunctionDefinition>(_statement))
+		return functionDefinitionCost;
+	else if (holds_alternative<If>(_statement))
+		return ifCost;
+	else if (holds_alternative<Switch>(_statement))
+		return switchCost + caseCost * std::get<Switch>(_statement).cases.size();
+	else if (holds_alternative<ForLoop>(_statement))
+		return forLoopCost;
+	else if (holds_alternative<Break>(_statement))
+		return breakCost;
+	else if (holds_alternative<Continue>(_statement))
+		return continueCost;
+	else if (holds_alternative<Leave>(_statement))
+		return leaveCost;
+	else if (holds_alternative<Block>(_statement))
+		return blockCost;
+	else
+		yulAssert(false, "If you add a new statement type, you must update CodeWeights.");
+}
+
+size_t CodeWeights::costOf(Expression const& _expression) const
+{
+	if (holds_alternative<FunctionCall>(_expression))
+		return functionCallCost;
+	else if (holds_alternative<Identifier>(_expression))
+		return identifierCost;
+	else if (holds_alternative<Literal>(_expression))
+		return literalCost;
+	else
+		yulAssert(false, "If you add a new expression type, you must update CodeWeights.");
+}
+
+
+size_t CodeSize::codeSize(Statement const& _statement, CodeWeights const& _weights)
+{
+	CodeSize cs(true, _weights);
 	cs.visit(_statement);
 	return cs.m_size;
 }
 
-size_t CodeSize::codeSize(Expression const& _expression)
+size_t CodeSize::codeSize(Expression const& _expression, CodeWeights const& _weights)
 {
-	CodeSize cs;
+	CodeSize cs(true, _weights);
 	cs.visit(_expression);
 	return cs.m_size;
 }
 
-size_t CodeSize::codeSize(Block const& _block)
+size_t CodeSize::codeSize(Block const& _block, CodeWeights const& _weights)
 {
-	CodeSize cs;
+	CodeSize cs(true, _weights);
 	cs(_block);
 	return cs.m_size;
 }
 
-size_t CodeSize::codeSizeIncludingFunctions(Block const& _block)
+size_t CodeSize::codeSizeIncludingFunctions(Block const& _block, CodeWeights const& _weights)
 {
-	CodeSize cs(false);
+	CodeSize cs(false, _weights);
 	cs(_block);
 	return cs.m_size;
 }
@@ -68,32 +109,14 @@ void CodeSize::visit(Statement const& _statement)
 {
 	if (holds_alternative<FunctionDefinition>(_statement) && m_ignoreFunctions)
 		return;
-	else if (
-		holds_alternative<If>(_statement) ||
-		holds_alternative<Break>(_statement) ||
-		holds_alternative<Continue>(_statement) ||
-		holds_alternative<Leave>(_statement)
-	)
-		m_size += 2;
-	else if (holds_alternative<ForLoop>(_statement))
-		m_size += 3;
-	else if (holds_alternative<Switch>(_statement))
-		m_size += 1 + 2 * std::get<Switch>(_statement).cases.size();
-	else if (!(
-		holds_alternative<Block>(_statement) ||
-		holds_alternative<ExpressionStatement>(_statement) ||
-		holds_alternative<Assignment>(_statement) ||
-		holds_alternative<VariableDeclaration>(_statement)
-	))
-		++m_size;
 
+	m_size += m_weights.costOf(_statement);
 	ASTWalker::visit(_statement);
 }
 
 void CodeSize::visit(Expression const& _expression)
 {
-	if (!holds_alternative<Identifier>(_expression))
-		++m_size;
+	m_size += m_weights.costOf(_expression);
 	ASTWalker::visit(_expression);
 }
 

libyul/optimiser/Metrics.h

@@ -30,33 +30,67 @@ struct Dialect;
 struct EVMDialect;
 
 /**
- * Metric for the size of code.
- * More specifically, the number of AST nodes.
- * Ignores function definitions while traversing the AST by default.
- * If you want to know the size of a function, you have to invoke this on its body.
+ * Weights to be assigned to specific yul statements and expressions by a metric.
  *
- * As an exception, the following AST elements have a cost of zero:
+ * The default values are meant to reflect specifically the number of AST nodes.
+ *
+ * The following AST elements have a default cost of zero (because the cleanup phase would
+ * remove them anyway or they are just wrappers around something else will be counted instead):
  *  - expression statement (only the expression inside has a cost)
  *  - block (only the statements inside have a cost)
  *  - variable references
  *  - variable declarations (only the right hand side has a cost)
  *  - assignments (only the value has a cost)
  *
- * As another exception, each statement incurs and additional cost of one
+ * Each statement incurs and additional cost of one
  * per jump/branch. This means if, break and continue statements have a cost of 2,
  * switch statements have a cost of 1 plus the number of cases times two,
  * and for loops cost 3.
+*/
+struct CodeWeights
+{
+	// Statements
+	size_t expressionStatementCost = 0;
+	size_t assignmentCost = 0;
+	size_t variableDeclarationCost = 0;
+	size_t functionDefinitionCost = 1;
+	size_t ifCost = 2;
+	size_t switchCost = 1;
+	size_t caseCost = 2;
+	size_t forLoopCost = 3;
+	size_t breakCost = 2;
+	size_t continueCost = 2;
+	size_t leaveCost = 2;
+	size_t blockCost = 0;
+
+	// Expressions
+	size_t functionCallCost = 1;
+	size_t identifierCost = 0;
+	size_t literalCost = 1;
+
+	size_t costOf(Statement const& _statement) const;
+	size_t costOf(Expression const& _expression) const;
+};
+
+/**
+ * Metric for the size of code.
+ * Ignores function definitions while traversing the AST by default.
+ * If you want to know the size of a function, you have to invoke this on its body.
+ *
+ * The cost of each statement and expression type is configurable via CodeWeights.
  */
 class CodeSize: public ASTWalker
 {
 public:
-	static size_t codeSize(Statement const& _statement);
-	static size_t codeSize(Expression const& _expression);
-	static size_t codeSize(Block const& _block);
-	static size_t codeSizeIncludingFunctions(Block const& _block);
+	static size_t codeSize(Statement const& _statement, CodeWeights const& _weights = {});
+	static size_t codeSize(Expression const& _expression, CodeWeights const& _weights = {});
+	static size_t codeSize(Block const& _block, CodeWeights const& _weights = {});
+	static size_t codeSizeIncludingFunctions(Block const& _block, CodeWeights const& _weights = {});
 
 private:
-	CodeSize(bool _ignoreFunctions = true): m_ignoreFunctions(_ignoreFunctions) {}
+	CodeSize(bool _ignoreFunctions = true, CodeWeights const& _weights = {}):
+		m_ignoreFunctions(_ignoreFunctions),
+		m_weights(_weights) {}
 
 	void visit(Statement const& _statement) override;
 	void visit(Expression const& _expression) override;
@@ -64,6 +98,7 @@ private:
 private:
 	bool m_ignoreFunctions;
 	size_t m_size = 0;
+	CodeWeights m_weights;
 };
 
 /**