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290 lines
9.1 KiB
290 lines
9.1 KiB
/* Block Copyright (C) 2000-2002 Jochen Hoenicke.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as published by
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* the Free Software Foundation; either version 2, or (at your option)
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* any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this program; see the file COPYING.LESSER. If not, write to
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* the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
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*
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* $Id$
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*/
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package net.sf.jode.bytecode;
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import java.io.PrintWriter;
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/**
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* <p>Represents a single basic block. It contains a list of
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* instructions and the successor blocks.</p>
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*
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* <p>All jump instructions must be at the end of the block. These
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* jump instructions are <code>opc_lookupswitch</code>,
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* <code>opc_if</code>xxx, <code>opc_jsr</code>, <code>opc_ret</code>,
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* <code>opc_</code>x<code>return</code> and <code>opc_return</code>.
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* An <code>opc_goto</code> is implicit if the basic block doesn't end
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* with a jump instructions, or if it ends with an conditional jump or
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* jsr.</p>
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*
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* <p>The jump instructions don't remember their destinations, instead
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* the Block does it. This are the successor block. There are
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* several cases:</p>
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*
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* <ul>
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* <li>Block ends with <code>opc_lookupswitch</code> with
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* <code>n</code> values. Then there must be <code>n+1</code>
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* successors where the first <code>n</code> successors correspond to
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* the values and the last successor is the default successor.</li>
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* <li>Block ends with <code>opc_if</code>xxx, then there must be two
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* successors: The first one is the successor if the condition evaluates
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* to true, the second one is for the false branch. </li>
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* <li>Block ends with <code>opc_jsr</code>, then there must be two
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* successors: The first one is the subroutine, the second is the next
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* block after the subroutine. </li>
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* <li>Block ends with <code>opc_</code>x</code>return</code> or
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* <code>opc_ret</code>, then there must no successor at all. </li>
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* <li>In any other case there must be exactly one successor.</li>
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* </ul>
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*
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* <p>If any successor is <code>null</code> it represents end of
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* method, i.e. a return instruction. You can also use
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* <code>null</code> successors for conditional jumps and switch
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* instruction. You normally shouldn't use <code>opc_return</code>
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* instructions. They are only necessary, if you want to return with
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* a non-empty stack. </p>
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*
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* @author Jochen Hoenicke
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* @see net.sf.jode.bytecode.BasicBlocks
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* @see net.sf.jode.bytecode.Instruction
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*/
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public final class Block {
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/**
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* The opcodes of the instructions in this block.
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*/
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private Instruction[] instrs;
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/**
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* The blockNr of successor blocks
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*/
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private Block[] succs;
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/**
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* The catching blocks. Set by BasicBlocks.
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*/
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Handler[] catchers;
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/**
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* The blockNr of this block. Set by BasicBlocks.
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*/
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int blockNr;
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/**
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* The number of items this block takes from the stack with
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* respect to the stack items at the beginning of the block.
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*/
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int maxpop;
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/**
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* The maximum number of items the stack may grow.
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*/
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int maxpush;
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/**
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* The difference stack items after the block minus stack items
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* before block.
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*/
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int delta;
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/**
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* The stack height at the beginning of this block.
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* Only valid after the block was inserted in a BasicBlocks and
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* the updateMaxStackLocals() of BasicBlocks was called.
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*/
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int stackHeight;
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/**
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* Creates a new block uninitialized block. You mustn't really
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* use it (except as successor for other blocks) until you have
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* set the code.
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*/
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public Block() {
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}
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/**
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* Gets the list of instructions. The returned list should not be
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* modified, except that the instructions (but not their opcodes)
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* may be modified.
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*/
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public Instruction[] getInstructions() {
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return instrs;
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}
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/**
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* Gets the successor array. The last successor is the next basic
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* block that is jumped to via goto or the default part of a
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* switch. For conditional jumps and jsrs the second successor gives
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* the destination.
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*/
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public Block[] getSuccs() {
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return succs;
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}
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/**
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* Gets the exception handlers whose try region contains this
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* block. You can't set them since they are calculated
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* automatically.
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* @return the exception handlers.
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* @see BasicBlocks#setBlocks
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*/
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public Handler[] getHandlers() {
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return catchers;
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}
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/**
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* Gets the block number. The block numbers are consecutive number
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* from 0 to the number of blocks in a method. The equation
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* <pre> BasicBlocks.getBlock()[i].getBlockNr() == i </pre>
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* always holds (as long as you don't do something dirty, like adding
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* the same block to different BasicBlocks, or to the same but more
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* than once).
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* @return the block number.
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*/
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public int getBlockNr() {
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return blockNr;
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}
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private void initCode() {
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int size = instrs.length;
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maxpop = maxpush = 0;
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int depth = 0;
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int poppush[] = new int[2];
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boolean needGoto = true;
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for (int i = 0; i < size; i++) {
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instrs[i].getStackPopPush(poppush);
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depth -= poppush[0];
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if (maxpop < -depth)
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maxpop = -depth;
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depth += poppush[1];
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if (maxpush < depth)
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maxpush = depth;
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int opcode = instrs[i].getOpcode();
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switch (opcode) {
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case Opcodes.opc_goto:
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throw new IllegalArgumentException("goto in block");
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case Opcodes.opc_lookupswitch:
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if (succs.length != instrs[i].getValues().length + 1)
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throw new IllegalArgumentException
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("number of successors for switch doesn't match");
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if (i != size - 1)
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throw new IllegalArgumentException
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("switch in the middle!");
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needGoto = false;
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break;
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case Opcodes.opc_ret: case Opcodes.opc_athrow:
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case Opcodes.opc_ireturn: case Opcodes.opc_lreturn:
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case Opcodes.opc_freturn: case Opcodes.opc_dreturn:
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case Opcodes.opc_areturn: case Opcodes.opc_return:
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if (succs.length != 0)
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throw new IllegalArgumentException
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("throw or return with successor.");
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if (i != size - 1)
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throw new IllegalArgumentException
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("return in the middle!");
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needGoto = false;
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break;
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case Opcodes.opc_ifeq: case Opcodes.opc_ifne:
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case Opcodes.opc_iflt: case Opcodes.opc_ifge:
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case Opcodes.opc_ifgt: case Opcodes.opc_ifle:
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case Opcodes.opc_if_icmpeq: case Opcodes.opc_if_icmpne:
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case Opcodes.opc_if_icmplt: case Opcodes.opc_if_icmpge:
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case Opcodes.opc_if_icmpgt: case Opcodes.opc_if_icmple:
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case Opcodes.opc_if_acmpeq: case Opcodes.opc_if_acmpne:
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case Opcodes.opc_ifnull: case Opcodes.opc_ifnonnull:
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case Opcodes.opc_jsr:
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if (succs.length != 2)
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throw new IllegalArgumentException
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("successors inappropriate for if/jsr");
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if (succs[0] == null && opcode == Opcodes.opc_jsr)
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throw new IllegalArgumentException
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("null successors inappropriate for jsr");
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if (i != size - 1)
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throw new IllegalArgumentException
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("if/jsr in the middle!");
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needGoto = false;
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}
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}
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delta = depth;
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if (needGoto && succs.length != 1)
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throw new IllegalArgumentException("no single successor block");
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}
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/**
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* Returns the stack height at the beginning of the block. This
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* is automatically calculated, when the block is inserted in a
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* basic block.
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*/
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public int getStackHeight () {
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return stackHeight;
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}
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public void getStackPopPush (int[] poppush) {
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poppush[0] = maxpop;
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poppush[1] = delta + maxpop;
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return;
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}
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/**
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* Set the code, i.e. instructions and successor blocks.
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* The instructions must be valid and match the successors.
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*/
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public void setCode(Instruction[] instrs, Block[] succs) {
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this.instrs = instrs;
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this.succs = succs;
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initCode();
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}
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public void dumpCode(PrintWriter output) {
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output.println(" "+this+":");
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for (int i = 0; i < instrs.length; i++) {
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Instruction instr = instrs[i];
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if (i == instrs.length - 1 && succs != null) {
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int opcode = instr.getOpcode();
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if (opcode == Opcodes.opc_lookupswitch) {
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// Special case for switch:
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output.println("\tswitch");
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int[] values = instr.getValues();
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for (int j = 0; j < values.length; j++)
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output.println("\t case"+values[j]
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+": goto "+succs[j]);
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output.println("\t default: goto"+
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succs[values.length]);
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return;
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} else if (succs.length > 1) {
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output.println("\t"+instr.getDescription()
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+" "+succs[0]);
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break;
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}
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}
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output.println("\t"+instr.getDescription());
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}
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if (succs != null && succs.length > 0) {
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if (succs[succs.length-1] == null)
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output.println("\treturn");
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else
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output.println("\tgoto "+succs[succs.length-1]);
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}
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}
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public String toString() {
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return "Block_"+blockNr;
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}
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}
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