framework/src/main/java/org/checkerframework/common/value/JavaExpressionOptimizer.java

package org.checkerframework.common.value;

import java.util.List;
import javax.lang.model.element.Element;
import javax.lang.model.type.TypeKind;
import org.checkerframework.dataflow.expression.FieldAccess;
import org.checkerframework.dataflow.expression.JavaExpression;
import org.checkerframework.dataflow.expression.JavaExpressionConverter;
import org.checkerframework.dataflow.expression.LocalVariable;
import org.checkerframework.dataflow.expression.MethodCall;
import org.checkerframework.dataflow.expression.ValueLiteral;
import org.checkerframework.framework.type.AnnotatedTypeFactory;

/**
 * Optimize the given JavaExpression. If the supplied factory is a {@code
 * ValueAnnotatedTypeFactory}, this implementation replaces any expression that the factory has an
 * exact value for, and does a small (not exhaustive) amount of constant-folding as well. If the
 * factory is some other factory, less optimization occurs.
 */
public class JavaExpressionOptimizer extends JavaExpressionConverter {

  /**
   * Annotated type factory. If it is a {@code ValueAnnotatedTypeFactory}, then more optimizations
   * are possible.
   */
  private final AnnotatedTypeFactory factory;

  /**
   * Creates a JavaExpressionOptimizer.
   *
   * @param factory an annotated type factory
   */
  public JavaExpressionOptimizer(AnnotatedTypeFactory factory) {
    this.factory = factory;
  }

  @Override
  protected JavaExpression visitFieldAccess(FieldAccess fieldAccessExpr, Void unused) {
    // Replace references to compile-time constant fields by the constant itself.
    if (fieldAccessExpr.isFinal()) {
      Object constant = fieldAccessExpr.getField().getConstantValue();
      if (constant != null && !(constant instanceof String)) {
        return new ValueLiteral(fieldAccessExpr.getType(), constant);
      }
    }
    return super.visitFieldAccess(fieldAccessExpr, unused);
  }

  @Override
  protected JavaExpression visitLocalVariable(LocalVariable localVarExpr, Void unused) {
    if (factory instanceof ValueAnnotatedTypeFactory) {
      Element element = localVarExpr.getElement();
      Long exactValue =
          ValueCheckerUtils.getExactValue(element, (ValueAnnotatedTypeFactory) factory);
      if (exactValue != null) {
        return new ValueLiteral(localVarExpr.getType(), exactValue.intValue());
      }
    }
    return super.visitLocalVariable(localVarExpr, unused);
  }

  @Override
  protected JavaExpression visitMethodCall(MethodCall methodCallExpr, Void unused) {
    JavaExpression optReceiver = convert(methodCallExpr.getReceiver());
    List<JavaExpression> optArguments = convert(methodCallExpr.getArguments());
    // Length of string literal: convert it to an integer literal.
    if (methodCallExpr.getElement().getSimpleName().contentEquals("length")
        && optReceiver instanceof ValueLiteral) {
      Object value = ((ValueLiteral) optReceiver).getValue();
      if (value instanceof String) {
        return new ValueLiteral(
            factory.types.getPrimitiveType(TypeKind.INT), ((String) value).length());
      }
    }
    return new MethodCall(
        methodCallExpr.getType(), methodCallExpr.getElement(), optReceiver, optArguments);
  }
}