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/*
* Javassist, a Java-bytecode translator toolkit.
* Copyright (C) 1999- Shigeru Chiba. All Rights Reserved.
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. Alternatively, the contents of this file may be used under
* the terms of the GNU Lesser General Public License Version 2.1 or later,
* or the Apache License Version 2.0.
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*/
package javassist.bytecode.analysis;
/**
* Represents the stack frame and local variable table at a particular point in time.
*
* @author Jason T. Greene
*/
public class Frame {
private Type[] locals;
private Type[] stack;
private int top;
private boolean jsrMerged;
private boolean retMerged;
/**
* Create a new frame with the specified local variable table size, and max stack size
*
* @param locals the number of local variable table entries
* @param stack the maximum stack size
*/
public Frame(int locals, int stack) {
this.locals = new Type[locals];
this.stack = new Type[stack];
}
/**
* Returns the local varaible table entry at index.
*
* @param index the position in the table
* @return the type if one exists, or null if the position is empty
*/
public Type getLocal(int index) {
return locals[index];
}
/**
* Sets the local variable table entry at index to a type.
*
* @param index the position in the table
* @param type the type to set at the position
*/
public void setLocal(int index, Type type) {
locals[index] = type;
}
/**
* Returns the type on the stack at the specified index.
*
* @param index the position on the stack
* @return the type of the stack position
*/
public Type getStack(int index) {
return stack[index];
}
/**
* Sets the type of the stack position
*
* @param index the position on the stack
* @param type the type to set
*/
public void setStack(int index, Type type) {
stack[index] = type;
}
/**
* Empties the stack
*/
public void clearStack() {
top = 0;
}
/**
* Gets the index of the type sitting at the top of the stack.
* This is not to be confused with a length operation which
* would return the number of elements, not the position of
* the last element.
*
* @return the position of the element at the top of the stack
*/
public int getTopIndex() {
return top - 1;
}
/**
* Returns the number of local variable table entries, specified
* at construction.
*
* @return the number of local variable table entries
*/
public int localsLength() {
return locals.length;
}
/**
* Gets the top of the stack without altering it
*
* @return the top of the stack
*/
public Type peek() {
if (top < 1)
throw new IndexOutOfBoundsException("Stack is empty");
return stack[top - 1];
}
/**
* Alters the stack to contain one less element and return it.
*
* @return the element popped from the stack
*/
public Type pop() {
if (top < 1)
throw new IndexOutOfBoundsException("Stack is empty");
return stack[--top];
}
/**
* Alters the stack by placing the passed type on the top
*
* @param type the type to add to the top
*/
public void push(Type type) {
stack[top++] = type;
}
/**
* Makes a shallow copy of this frame, i.e. the type instances will
* remain the same.
*
* @return the shallow copy
*/
public Frame copy() {
Frame frame = new Frame(locals.length, stack.length);
System.arraycopy(locals, 0, frame.locals, 0, locals.length);
System.arraycopy(stack, 0, frame.stack, 0, stack.length);
frame.top = top;
return frame;
}
/**
* Makes a shallow copy of the stack portion of this frame. The local
* variable table size will be copied, but its contents will be empty.
*
* @return the shallow copy of the stack
*/
public Frame copyStack() {
Frame frame = new Frame(locals.length, stack.length);
System.arraycopy(stack, 0, frame.stack, 0, stack.length);
frame.top = top;
return frame;
}
/**
* Merges all types on the stack of this frame instance with that of the specified frame.
* The local variable table is left untouched.
*
* @param frame the frame to merge the stack from
* @return true if any changes where made
*/
public boolean mergeStack(Frame frame) {
boolean changed = false;
if (top != frame.top)
throw new RuntimeException("Operand stacks could not be merged, they are different sizes!");
for (int i = 0; i < top; i++) {
if (stack[i] != null) {
Type prev = stack[i];
Type merged = prev.merge(frame.stack[i]);
if (merged == Type.BOGUS)
throw new RuntimeException("Operand stacks could not be merged due to differing primitive types: pos = " + i);
stack[i] = merged;
// always replace the instance in case a multi-interface type changes to a normal Type
if ((! merged.equals(prev)) || merged.popChanged()) {
changed = true;
}
}
}
return changed;
}
/**
* Merges all types on the stack and local variable table of this frame with that of the specified
* type.
*
* @param frame the frame to merge with
* @return true if any changes to this frame where made by this merge
*/
public boolean merge(Frame frame) {
boolean changed = false;
// Local variable table
for (int i = 0; i < locals.length; i++) {
if (locals[i] != null) {
Type prev = locals[i];
Type merged = prev.merge(frame.locals[i]);
// always replace the instance in case a multi-interface type changes to a normal Type
locals[i] = merged;
if (! merged.equals(prev) || merged.popChanged()) {
changed = true;
}
} else if (frame.locals[i] != null) {
locals[i] = frame.locals[i];
changed = true;
}
}
changed |= mergeStack(frame);
return changed;
}
public String toString() {
StringBuffer buffer = new StringBuffer();
buffer.append("locals = [");
for (int i = 0; i < locals.length; i++) {
buffer.append(locals[i] == null ? "empty" : locals[i].toString());
if (i < locals.length - 1)
buffer.append(", ");
}
buffer.append("] stack = [");
for (int i = 0; i < top; i++) {
buffer.append(stack[i]);
if (i < top - 1)
buffer.append(", ");
}
buffer.append("]");
return buffer.toString();
}
/**
* Whether or not state from the source JSR instruction has been merged
*
* @return true if JSR state has been merged
*/
boolean isJsrMerged() {
return jsrMerged;
}
/**
* Sets whether of not the state from the source JSR instruction has been merged
*
* @param jsrMerged true if merged, otherwise false
*/
void setJsrMerged(boolean jsrMerged) {
this.jsrMerged = jsrMerged;
}
/**
* Whether or not state from the RET instruction, of the subroutine that was jumped
* to has been merged.
*
* @return true if RET state has been merged
*/
boolean isRetMerged() {
return retMerged;
}
/**
* Sets whether or not state from the RET instruction, of the subroutine that was jumped
* to has been merged.
*
* @param retMerged true if RET state has been merged
*/
void setRetMerged(boolean retMerged) {
this.retMerged = retMerged;
}
}
