// ASM: a very small and fast Java bytecode manipulation framework
// Copyright (c) 2000-2011 INRIA, France Telecom
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package scala.tools.asm.tree.analysis;

import java.util.List;
import scala.tools.asm.Opcodes;
import scala.tools.asm.Type;
import scala.tools.asm.tree.AbstractInsnNode;
import scala.tools.asm.tree.TryCatchBlockNode;

/**
 * A semantic bytecode interpreter. More precisely, this interpreter only manages the computation of
 * values from other values: it does not manage the transfer of values to or from the stack, and to
 * or from the local variables. This separation allows a generic bytecode {@link Analyzer} to work
 * with various semantic interpreters, without needing to duplicate the code to simulate the
 * transfer of values.
 *
 * @param <V> type of the Value used for the analysis.
 * @author Eric Bruneton
 */
public abstract class Interpreter<V extends Value> {

  /**
   * The ASM API version supported by this interpreter. The value of this field must be one of the
   * {@code ASM}<i>x</i> values in {@link Opcodes}.
   */
  protected final int api;

  /**
   * Constructs a new {@link Interpreter}.
   *
   * @param api the ASM API version supported by this interpreter. Must be one of the {@code
   *     ASM}<i>x</i> values in {@link Opcodes}.
   */
  protected Interpreter(final int api) {
    this.api = api;
  }

  /**
   * Creates a new value that represents the given type.
   *
   * <p>Called for method parameters (including <code>this</code>), exception handler variable and
   * with <code>null</code> type for variables reserved by long and double types.
   *
   * <p>An interpreter may choose to implement one or more of {@link
   * Interpreter#newReturnTypeValue(Type)}, {@link Interpreter#newParameterValue(boolean, int,
   * Type)}, {@link Interpreter#newEmptyValue(int)}, {@link
   * Interpreter#newExceptionValue(TryCatchBlockNode, Frame, Type)} to distinguish different types
   * of new value.
   *
   * @param type a primitive or reference type, or {@literal null} to represent an uninitialized
   *     value.
   * @return a value that represents the given type. The size of the returned value must be equal to
   *     the size of the given type.
   */
  public abstract V newValue(Type type);

  /**
   * Creates a new value that represents the given parameter type. This method is called to
   * initialize the value of a local corresponding to a method parameter in a frame.
   *
   * <p>By default, calls <code>newValue(type)</code>.
   *
   * @param isInstanceMethod {@literal true} if the method is non-static.
   * @param local the local variable index.
   * @param type a primitive or reference type.
   * @return a value that represents the given type. The size of the returned value must be equal to
   *     the size of the given type.
   */
  public V newParameterValue(final boolean isInstanceMethod, final int local, final Type type) {
    return newValue(type);
  }

  /**
   * Creates a new value that represents the given return type. This method is called to initialize
   * the return type value of a frame.
   *
   * <p>By default, calls <code>newValue(type)</code>.
   *
   * @param type a primitive or reference type.
   * @return a value that represents the given type. The size of the returned value must be equal to
   *     the size of the given type.
   */
  public V newReturnTypeValue(final Type type) {
    return newValue(type);
  }

  /**
   * Creates a new uninitialized value for a local variable. This method is called to initialize the
   * value of a local that does not correspond to a method parameter, and to reset one half of a
   * size-2 value when the other half is assigned a size-1 value.
   *
   * <p>By default, calls <code>newValue(null)</code>.
   *
   * @param local the local variable index.
   * @return a value representing an uninitialized value. The size of the returned value must be
   *     equal to 1.
   */
  public V newEmptyValue(final int local) {
    return newValue(null);
  }

  /**
   * Creates a new value that represents the given exception type. This method is called to
   * initialize the exception value on the call stack at the entry of an exception handler.
   *
   * <p>By default, calls <code>newValue(exceptionType)</code>.
   *
   * @param tryCatchBlockNode the exception handler.
   * @param handlerFrame the exception handler frame.
   * @param exceptionType the exception type handled by this handler.
   * @return a value that represents the given {@code exceptionType}. The size of the returned value
   *     must be equal to 1.
   */
  public V newExceptionValue(
      final TryCatchBlockNode tryCatchBlockNode,
      final Frame<V> handlerFrame,
      final Type exceptionType) {
    return newValue(exceptionType);
  }

  /**
   * Interprets a bytecode instruction without arguments. This method is called for the following
   * opcodes:
   *
   * <p>ACONST_NULL, ICONST_M1, ICONST_0, ICONST_1, ICONST_2, ICONST_3, ICONST_4, ICONST_5,
   * LCONST_0, LCONST_1, FCONST_0, FCONST_1, FCONST_2, DCONST_0, DCONST_1, BIPUSH, SIPUSH, LDC, JSR,
   * GETSTATIC, NEW
   *
   * @param insn the bytecode instruction to be interpreted.
   * @return the result of the interpretation of the given instruction.
   * @throws AnalyzerException if an error occurred during the interpretation.
   */
  public abstract V newOperation(AbstractInsnNode insn) throws AnalyzerException;

  /**
   * Interprets a bytecode instruction that moves a value on the stack or to or from local
   * variables. This method is called for the following opcodes:
   *
   * <p>ILOAD, LLOAD, FLOAD, DLOAD, ALOAD, ISTORE, LSTORE, FSTORE, DSTORE, ASTORE, DUP, DUP_X1,
   * DUP_X2, DUP2, DUP2_X1, DUP2_X2, SWAP
   *
   * @param insn the bytecode instruction to be interpreted.
   * @param value the value that must be moved by the instruction.
   * @return the result of the interpretation of the given instruction. The returned value must be
   *     {@code equal} to the given value.
   * @throws AnalyzerException if an error occurred during the interpretation.
   */
  public abstract V copyOperation(AbstractInsnNode insn, V value) throws AnalyzerException;

  /**
   * Interprets a bytecode instruction with a single argument. This method is called for the
   * following opcodes:
   *
   * <p>INEG, LNEG, FNEG, DNEG, IINC, I2L, I2F, I2D, L2I, L2F, L2D, F2I, F2L, F2D, D2I, D2L, D2F,
   * I2B, I2C, I2S, IFEQ, IFNE, IFLT, IFGE, IFGT, IFLE, TABLESWITCH, LOOKUPSWITCH, IRETURN, LRETURN,
   * FRETURN, DRETURN, ARETURN, PUTSTATIC, GETFIELD, NEWARRAY, ANEWARRAY, ARRAYLENGTH, ATHROW,
   * CHECKCAST, INSTANCEOF, MONITORENTER, MONITOREXIT, IFNULL, IFNONNULL
   *
   * @param insn the bytecode instruction to be interpreted.
   * @param value the argument of the instruction to be interpreted.
   * @return the result of the interpretation of the given instruction.
   * @throws AnalyzerException if an error occurred during the interpretation.
   */
  public abstract V unaryOperation(AbstractInsnNode insn, V value) throws AnalyzerException;

  /**
   * Interprets a bytecode instruction with two arguments. This method is called for the following
   * opcodes:
   *
   * <p>IALOAD, LALOAD, FALOAD, DALOAD, AALOAD, BALOAD, CALOAD, SALOAD, IADD, LADD, FADD, DADD,
   * ISUB, LSUB, FSUB, DSUB, IMUL, LMUL, FMUL, DMUL, IDIV, LDIV, FDIV, DDIV, IREM, LREM, FREM, DREM,
   * ISHL, LSHL, ISHR, LSHR, IUSHR, LUSHR, IAND, LAND, IOR, LOR, IXOR, LXOR, LCMP, FCMPL, FCMPG,
   * DCMPL, DCMPG, IF_ICMPEQ, IF_ICMPNE, IF_ICMPLT, IF_ICMPGE, IF_ICMPGT, IF_ICMPLE, IF_ACMPEQ,
   * IF_ACMPNE, PUTFIELD
   *
   * @param insn the bytecode instruction to be interpreted.
   * @param value1 the first argument of the instruction to be interpreted.
   * @param value2 the second argument of the instruction to be interpreted.
   * @return the result of the interpretation of the given instruction.
   * @throws AnalyzerException if an error occurred during the interpretation.
   */
  public abstract V binaryOperation(AbstractInsnNode insn, V value1, V value2)
      throws AnalyzerException;

  /**
   * Interprets a bytecode instruction with three arguments. This method is called for the following
   * opcodes:
   *
   * <p>IASTORE, LASTORE, FASTORE, DASTORE, AASTORE, BASTORE, CASTORE, SASTORE
   *
   * @param insn the bytecode instruction to be interpreted.
   * @param value1 the first argument of the instruction to be interpreted.
   * @param value2 the second argument of the instruction to be interpreted.
   * @param value3 the third argument of the instruction to be interpreted.
   * @return the result of the interpretation of the given instruction.
   * @throws AnalyzerException if an error occurred during the interpretation.
   */
  public abstract V ternaryOperation(AbstractInsnNode insn, V value1, V value2, V value3)
      throws AnalyzerException;

  /**
   * Interprets a bytecode instruction with a variable number of arguments. This method is called
   * for the following opcodes:
   *
   * <p>INVOKEVIRTUAL, INVOKESPECIAL, INVOKESTATIC, INVOKEINTERFACE, MULTIANEWARRAY and
   * INVOKEDYNAMIC
   *
   * @param insn the bytecode instruction to be interpreted.
   * @param values the arguments of the instruction to be interpreted.
   * @return the result of the interpretation of the given instruction.
   * @throws AnalyzerException if an error occurred during the interpretation.
   */
  public abstract V naryOperation(AbstractInsnNode insn, List<? extends V> values)
      throws AnalyzerException;

  /**
   * Interprets a bytecode return instruction. This method is called for the following opcodes:
   *
   * <p>IRETURN, LRETURN, FRETURN, DRETURN, ARETURN
   *
   * @param insn the bytecode instruction to be interpreted.
   * @param value the argument of the instruction to be interpreted.
   * @param expected the expected return type of the analyzed method.
   * @throws AnalyzerException if an error occurred during the interpretation.
   */
  public abstract void returnOperation(AbstractInsnNode insn, V value, V expected)
      throws AnalyzerException;

  /**
   * Merges two values. The merge operation must return a value that represents both values (for
   * instance, if the two values are two types, the merged value must be a common super type of the
   * two types. If the two values are integer intervals, the merged value must be an interval that
   * contains the previous ones. Likewise for other types of values).
   *
   * @param value1 a value.
   * @param value2 another value.
   * @return the merged value. If the merged value is equal to {@code value1}, this method
   *     <i>must</i> return {@code value1}.
   */
  public abstract V merge(V value1, V value2);
}
