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260 lines
8.4 KiB
260 lines
8.4 KiB
/*
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* StructuredBlock (c) 1998 Jochen Hoenicke
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*
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* You may distribute under the terms of the GNU General Public License.
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*
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* IN NO EVENT SHALL JOCHEN HOENICKE BE LIABLE TO ANY PARTY FOR DIRECT,
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* INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF
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* THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF JOCHEN HOENICKE
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* HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* JOCHEN HOENICKE SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
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* PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS ON AN "AS IS"
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* BASIS, AND JOCHEN HOENICKE HAS NO OBLIGATION TO PROVIDE MAINTENANCE,
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* SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
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*
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* $Id$
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*/
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package jode.flow;
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/**
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* A structured block is the building block of the source programm.
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* For every program construct like if, while, try, or blocks there is
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* a corresponding structured block.
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*
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* Some of these Block are only intermediate representation, that get
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* converted to another block later.
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*
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* Every block has to handle the local variables that it contains.
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* This is done by the in/out vectors and the local variable structure
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* themself. Every local variable used in this structured block is
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* either in or out.
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*
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* There are following types of structured blocks:
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* <ul>
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* <li>if-then-(else)-block (IfThenElseBlock)
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* <li>(do)-while/for-block (LoopBlock)
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* <li>switch-block (SwitchBlock)
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* <li>try-catch-block (CatchBlock)
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* <li>try-finally-block (FinallyBlock)
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* <li>synchronized-block (SynchronizedBlock)
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* <li>one-instruction (InstructionBlock)
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* <li>empty-block (EmptyBlock)
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* <li>multi-blocks-block (SequentialBlock)
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* </ul>
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*/
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public abstract class StructuredBlock {
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/* Invariants:
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* in.intersection(out) = empty
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* outer != null => flowblock = outer.flowblock
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* outer == null => flowblock.block = this
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* jump == null => outer != null
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* either getNextBlock() != null
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* or getNextFlowBlock() != null or outer == null
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* either outer.getNextBlock(this) != null
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* or outer.getNextFlowBlock(this) != null
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*/
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/**
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* The in locals. This are the locals, which are used in this
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* block and whose values may be the result of a assignment
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* outside of the whole flow block. That means, that there is a
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* path from the start of the current flow block, on which the
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* local variable is never assigned
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*/
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VariableSet in;
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/**
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* The out locals. This are the locals, which must be overwritten
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* until the end of this block. That means, that all paths form
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* the start of the current flow block to the end of this
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* structured block contain a (unconditional) assignment to this
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* local
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*/
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VariableSet out;
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/**
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* The variable set containing all variables that must be defined
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* in this block (or maybe an outer block, this changes as the
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* blocks are put together).
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*/
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VariableSet defineHere;
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/**
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* The surrounding structured block. If this is the outermost
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* block in a flow block, outer is null. */
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StructuredBlock outer;
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/**
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* The flow block in which this structured block lies.
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*/
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FlowBlock flowblock;
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/**
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* The jump that follows on this block, or null if there is no
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* jump, but the control flows normal (only allowed if
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* getNextBlock != null).
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*/
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Jump jump;
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/**
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* Returns the block where the control will normally flow to, when
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* this block is finished (not ignoring the jump after this block).
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*/
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StructuredBlock getNextBlock() {
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if (jump != null)
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return null;
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if (outer != null)
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outer.getNextBlock(this);
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else
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return null;
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}
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/**
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* Returns the flow block where the control will normally flow to,
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* when this block is finished (not ignoring the jump after this
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* block).
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* @return null, if the control flows into a non empty structured
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* block or if this is the outermost block.
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*/
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FlowBlock getNextFlowBlock() {
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if (jump != null)
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return jump.destination;
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if (outer != null)
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outer.getNextFlowBlock(this);
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else
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return null;
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}
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/**
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* Checks if the jump to the outside has correct monitorexit and
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* jsr instructions attached.
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* @return null, if everything is okay, and a diagnostic message that
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* should be put in a comment otherwise.
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*/
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String checkJump(Jump jump) {
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if (outer != null)
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return outer.checkJump(jump);
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else if (jump.hasAttachments())
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return "Unknown attachments: "+jump.describeAttachments()
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else
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return null;
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}
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/**
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* Returns the block where the control will normally flow to, when
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* the given sub block is finished (<em>not</em> ignoring the jump
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* after this block). (This is overwritten by SequentialBlock and
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* SwitchBlock). If this isn't called with a direct sub block,
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* the behaviour is undefined, so take care.
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* @return null, if the control flows to another FlowBlock. */
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StructuredBlock getNextBlock(StructuredBlock subBlock) {
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return getNextBlock();
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}
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FlowBlock getNextFlowBlock(StructuredBlock subBlock) {
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return getNextFlowBlock();
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}
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/**
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* Replaces the given sub block with a new block.
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* @param oldBlock the old sub block.
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* @param newBlock the new sub block.
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* @return false, if oldBlock wasn't a direct sub block.
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*/
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boolean replaceSubBlock(StructuredBlock oldBlock,
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StructuredBlock newBlock) {
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return false;
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}
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/**
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* Returns all sub block of this structured block.
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*/
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StructuredBlock[] getSubBlocks() {
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return new StructuredBlock[0];
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}
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/**
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* Returns if this block contains the given block.
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* @param child the block which should be contained by this block.
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* @return false, if child is null, or is not contained in this block.
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*/
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boolean contains(StructuredBlock child) {
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while (child != this && child != null)
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child = child.outer;
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return (child == this);
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}
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/**
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* Removes the jump after this structured block. This does also update
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* the successors vector of the flow block.
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*/
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public void removeJump() {
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if (jump != null) {
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flowBlock.removeSuccessor(jump);
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jump = null;
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}
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}
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/**
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* This function replaces sb with this block. It copies outer and
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* the following jump from sb, and updates them, so they know that
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* sb was replaced.
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* The jump field of sb is removed afterwards. You have to replace
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* sb.outer or mustn't use sb anymore.
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* @param sb The structured block that should be replaced.
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*/
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public void replace(StructuredBlock sb) {
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in = sb.in;
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out = sb.out;
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defineHere = sb.defineHere;
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outer = sb.outer;
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flowBlock = sb.flowBlock;
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jump = sb.jump;
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if (jump != null) {
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jump.parent = this;
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sb.jump = null;
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}
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if (outer != null) {
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outer.replaceSubBlock(sb, this);
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} else {
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flowBlock.block = this;
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}
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}
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/**
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* Determines if there is a sub block, that flows through to the end
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* of this block. If this returns true, you know that jump is null.
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* @return true, if the jump may be safely changed.
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*/
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public boolean jumpMayBeChanged() {
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return false;
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}
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/**
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* Get the unique predecessor which mustn't be a conditional jump
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* @return the predecessor or null if there isn't a such a thing
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*/
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public StructuredBlock getSimpleUniquePredecessor() {
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SequentialBlock sequ;
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if (outer instanceof SequentialBlock) {
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if (outer.getSubBlocks()[1] == this)
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return outer.getSubBlocks()[0];
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else if (outer.outer instanceof SequentialBlock)
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return outer.outer.getSubBlocks[0];
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}
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return null;
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}
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/**
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* Print the source code for this structured block. This may be
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* called only once, because it remembers which local variables
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* were declared. */
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public abstract void dumpSource(TabbedPrintWriter writer)
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throws java.io.IOException;
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}
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