[yul-phaser] Add ProgramSize metric

tools/yulPhaser/FitnessMetrics.cpp

@@ -16,3 +16,13 @@
 */
 
 #include <tools/yulPhaser/FitnessMetrics.h>
+
+using namespace std;
+using namespace solidity::phaser;
+
+size_t ProgramSize::evaluate(Chromosome const& _chromosome) const
+{
+	Program programCopy = m_program;
+	programCopy.optimise(_chromosome.optimisationSteps());
+	return programCopy.codeSize();
+}

tools/yulPhaser/FitnessMetrics.h

@@ -21,6 +21,7 @@
 #pragma once
 
 #include <tools/yulPhaser/Chromosome.h>
+#include <tools/yulPhaser/Program.h>
 
 #include <cstddef>
 
@@ -45,4 +46,19 @@ public:
 	virtual size_t evaluate(Chromosome const& _chromosome) const = 0;
 };
 
+/**
+ * Fitness metric based on the size of a specific program after applying the optimisations from the
+ * chromosome to it.
+ */
+class ProgramSize: public FitnessMetric
+{
+public:
+	ProgramSize(Program _program): m_program(std::move(_program)) {}
+
+	size_t evaluate(Chromosome const& _chromosome) const override;
+
+private:
+	Program m_program;
+};
+
 }