soot.grimp.PrecedenceTest Maven / Gradle / Ivy

package soot.grimp;

/*-
 * #%L
 * Soot - a J*va Optimization Framework
 * %%
 * Copyright (C) 2003 Ondrej Lhotak
 * %%
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 2.1 of the
 * License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Lesser Public License for more details.
 * 
 * You should have received a copy of the GNU General Lesser Public
 * License along with this program.  If not, see
 * .
 * #L%
 */

import soot.Value;
import soot.ValueBox;

/**
 * Provides static helper methods to indicate if parenthesization is required.
 *
 * If your sub-expression has strictly higher precedence than you, then no brackets are required: 2 + (4 * 5) = 2 + 4 * 5 is
 * unambiguous, because * has precedence 800 and + has precedence 700.
 *
 * If your subexpression has lower precedence than you, then brackets are required; otherwise you will bind to your
 * grandchild instead of the subexpression. 2 * (4 + 5) without brackets would mean (2 * 4) + 5.
 *
 * For a binary operation, if your left sub-expression has the same precedence as you, no brackets are needed, since binary
 * operations are all left-associative. If your right sub-expression has the same precedence than you, then brackets are
 * needed to reproduce the parse tree (otherwise, parsing will give e.g. (2 + 4) + 5 instead of the 2 + (4 + 5) that you had
 * to start with.) This is OK for integer addition and subtraction, but not OK for floating point multiplication. To be safe,
 * let's put the brackets on.
 *
 * For the high-precedence operations, I've assigned precedences of 950 to field reads and invoke expressions (.), as well as
 * array reads ([]). I've assigned 850 to cast, newarray and newinvoke.
 *
 * The Dava DCmp?Expr precedences look fishy to me; I've assigned DLengthExpr a precedence of 950, because it looks like it
 * should parse like a field read to me.
 *
 * Basically, the only time I can see that brackets should be required seems to occur when a cast or a newarray occurs as a
 * subexpression of an invoke or field read; hence 850 and 950. -PL
 */
public class PrecedenceTest {
  public static boolean needsBrackets(ValueBox subExprBox, Value expr) {
    Value sub = subExprBox.getValue();
    if (!(sub instanceof Precedence)) {
      return false;
    }
    Precedence subP = (Precedence) sub;
    Precedence exprP = (Precedence) expr;
    return subP.getPrecedence() < exprP.getPrecedence();
  }

  public static boolean needsBracketsRight(ValueBox subExprBox, Value expr) {
    Value sub = subExprBox.getValue();
    if (!(sub instanceof Precedence)) {
      return false;
    }
    Precedence subP = (Precedence) sub;
    Precedence exprP = (Precedence) expr;
    return subP.getPrecedence() <= exprP.getPrecedence();
  }
}