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507 lines
19 KiB
507 lines
19 KiB
/*
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* FlowBlock (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 flow block is the structure of which the flow graph consists. A
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* flow block contains structured code together with some conditional
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* or unconditional jumps to the head of other flow blocks.
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*
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* We do a T1/T2 analysis to combine all flow blocks to a single. If
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* the graph isn't reducible that doesn't work, but java can only
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* produce reducible flow graphs.
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*/
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public class FlowBlock {
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/**
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* The starting address of this flow block. This is mainly used
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* to produce the source code in code order.
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*/
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int addr;
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/**
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* The outermost structructed block in this flow block.
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*/
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StructuredBlock block;
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/**
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* The last modified structured block.
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*/
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StructuredBlock lastModified;
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/**
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* All Jumps that this flow block contains. The objects may be
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* null, if they were marked as deleted. */
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Vector successors;
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/**
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* This is a vector of flow blocks, which reference this block.
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* Only if this vector contains exactly one element, it can be
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* moved into the preceding flow block.
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*/
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Vector predecessors;
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/**
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* This method optimizes the jumps to successor.
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* Returns the new appendBlock, it may have changed.
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*/
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public StructuredBlock optimizeJumps(FlowBlock successor,
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StructuredBlock appendBlock) {
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Enumeration enum = successors.elements();
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while (enum.hasMoreElements()) {
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Jump jump = (Jump) enum.nextElement();
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if (jump == null || jump.destination != successor)
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continue;
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/* if the jump is the jump of the appendBlock, skip it.
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*/
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if (jump == appendBlock.jump)
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continue;
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/* Note: jump.parent.outer != null, since appendBlock is
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* an outer block of jump.parent
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*/
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/* remove all jumps to the successor which have the successor
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* as getNextFlowBlock(). */
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if (jump.parent.outer.getNextFlowBlock(jump.parent) == successor)
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jump.parent.removeJump();
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/* replace all conditional jumps to the successor, which
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* are followed by a block which has the end of the block
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* as normal successor, with "if (not condition) block".
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*/
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if (jump.parent instanceof ConditionalBlock &&
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jump.parent.outer instanceof SequentialBlock &&
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jump.parent.outer.getSubBlocks()[0] = jump.parent &&
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jump.parent.outer.getNextFlowBlock() == successor) {
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ConditionalBlock cb = (ConditionalBlock) jump.parent;
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cb.removeJump();
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SequentialBlock sequBlock =
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(SequentialBlock) cb.outer;
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IfThenElseBlock newIfBlock =
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new IfThenElseBlock(cb.getCondition().negate(),
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sequBlock.getSubBlocks()[1], null);
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newIfBlock.replace(sequBlock);
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if (appendBlock == sequBlock)
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appendBlock = newIfBlock;
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continue;
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}
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/* if the successor is the dummy return instruction, replace all
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* jumps with a return.
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*/
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if (successor.block.instanceof ReturnBlock) {
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SequentialBlock sequBlock = new SequentialBlock();
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StructuredBlock prevBlock = jump.parent;
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prevBlock.removeJump();
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sequBlock.replace(prevBlock);
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sequBlock.setFirst(prevBlock);
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sequBlock.setSecond(new ReturnBlock());
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continue;
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}
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/* If this is a conditional jump, the first instruction of
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* a while and the condition of the while is true, use
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* the condition as while condition.
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*/
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/* This is the first instruction in a while block */
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if (jump.parent instanceof ConditionalBlock &&
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jump.parent.outer instanceof SequentialBlock &&
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jump.parent.outer.getSubBlocks()[0] == this &&
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jump.parent.outer.outer instanceof LoopBlock) {
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ConditionalBlock cb = (ConditionalBlock) jump.parent;
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LoopBlock loopBlock = (LoopBlock) cb.outer.outer;
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if (loopBlock.getCondition() == LoopBlock.TRUE &&
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loopBlock.getType() != LoopBlock.DOWHILE &&
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loopBlock.getNextFlowBlock() == successor) {
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cb.removeJump();
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loopBlock.setCondition(cb);
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cb.outer.getSubBlocks()[1].replace(cb.outer);
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/* cb and cb.outer are not used any more */
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/* Note that cb.outer != appendBlock because
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* appendBlock contains loopBlock
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*/
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}
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}
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/* Now the same for the empty loop. In this case there is
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* no sequential block.
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*/
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if (jump.parent instanceof ConditionalBlock &&
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jump.parent.outer instanceof LoopBlock) {
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ConditionalBlock cb = (ConditionalBlock) jump.parent;
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LoopBlock loopBlock = (LoopBlock) cb.outer;
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if (loopBlock.getCondition() == LoopBlock.TRUE &&
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loopBlock.getType() != LoopBlock.DOWHILE &&
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loopBlock.getNextFlowBlock() == successor) {
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cb.removeJump();
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loopBlock.setCondition(cb);
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EmptyBlock empty = new EmptyBlock();
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empty.replace(cb);
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/* cb is not used any more */
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}
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}
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/* if there are jumps in a while block or switch block and the
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* while/switch block is followed by a jump to successor or has
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* successor as getNextFlowBlock(), replace jump with break to
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* the innermost such while/switch block.
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*
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* If the switch block hasn't been breaked before we could
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* take some heuristics and add a jump after the switch to
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* succesor, so that the above succeeds.
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*/
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int breaklevel = 0;
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for (StructuredBlock surrounder = jump.parent.outer;
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surrounder != null; surrounder = surrounder.outer) {
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if (surrounder instanceof BreakableBlock) {
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breaklevel++;
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if (surrounder.getNextFlowBlock() == successor ||
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surrounder.jumpMayBeChanged()) {
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SequentialBlock sequBlock = new SequentialBlock();
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StructuredBlock prevBlock = jump.parent;
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if (surrounder.getNextFlowBlock() != successor) {
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surrounder.jump = jump;
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prevBlock.jump = null;
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jump.parent = surrounder;
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} else {
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prevBlock.removeJump();
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}
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sequBlock.replace(prevBlock);
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sequBlock.setFirst(prevBlock);
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sequBlock.setSecond(new BreakBlock(surrounder,
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breaklevel > 1));
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continue;
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}
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}
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}
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/* if there are jumps in an if-then block, which
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* have as normal successor the end of the if-then block, and
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* the if-then block is followed by a single block, then replace
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* the if-then block with a if-then-else block and remove the
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* unconditional jump.
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*/
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StructuredBlock elseBlock =
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jump.parent.outer.getNextBlock(jump.parent);
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if (elseBlock != null &&
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elseBlock.outer != null &&
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elseBlock.outer instanceof SequentialBlock &&
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elseBlock.outer.getSubBlocks()[0] instanceof IfThenElseBlock &&
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(elseBlock.outer.getNextFlowBlock() == successor ||
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elseBlock.outer.jumpMayBeChanged()) {
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IfThenElseBlock ifBlock =
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(IfThenElseBlock)elseBlock.outer.getSubBlocks()[0];
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if (ifBlock.getElseBlock() == null) {
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if (elseBlock.getNextFlowBlock() != successor) {
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elseBlock.outer.jump = jump;
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jump.parent.jump = null;
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jump.parent = elseBlock.outer;
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} else {
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jump.parent.removeJump();
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}
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ifBlock.replace(elseBlock.outer)
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ifBlock.setElseBlock(elseBlock);
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if (appendBlock = elseBlock.outer)
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appendBlock = ifBlock;
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}
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}
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}
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return appendBlock;
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}
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/**
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* Updates the in/out-Vectors of the structured block of the
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* successing flow block simultanous to a T1 transformation.
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* @param successor The flow block which is unified with this flow
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* block.
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*/
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void updateInOut (FlowBlock successor, boolean t1Transformation) {
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/* First get the out vectors of all jumps to successor and
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* calculate the intersection.
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*/
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VariableSet allOuts = new VariableSet();
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VariableSet intersectOut = null;
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Enumeration enum = successors;
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while (enum.hasMoreElement()) {
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Jump jump = (Jump) enum.nextElement();
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if (jump == null || jump.destination != successor)
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continue;
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allOuts.union(jump.parent.out);
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if (intersectOut == null)
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intersectOut = jump.parent.out;
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else
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intersectOut = intersectOut.intersect(jump.parent.out);
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}
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/* Now work on each block of the successor */
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Stack todo = new Stack();
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todo.push(successor.block);
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while (!todo.empty()) {
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StructuredBlock block = (StructuredBlock) todo.pop();
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StructuredBlock[] subBlocks = block.getSubBlocks();
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for (int i=0; i<subBlocks.length; i++)
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todo.push(subBlocks[i]);
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/* Merge the locals used in successing block with those written
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* by this blocks
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*/
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block.in.merge(allOuts);
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if (t1Transformation) {
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/* Now update in and out set of successing block */
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block.in.subtract(intersectOut);
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block.out.add(intersectOut);
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}
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}
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}
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/* Special cases:
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*
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* try-header
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* |- first instruction
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* | ...
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* | last instruction
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* |- optional jump (last+1)
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* | ...
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* `- catch block
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*
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* A try block may have many try-headers with different catch blocks
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* and there may be a finally block:
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*
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* try-header any
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* | try-header
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* |--|- first instruction
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* | | ...
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* | | every jump to outside is preceded by jsr finally
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* | | ...
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* | | last instruction
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* | |- optional jump after catch block (last+1)
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* | | ... |
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* | `- catch block |
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* | ... |
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* | ,-----------------'
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* | |-jump after all catch blocks
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* | v
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* | jsr finally -----------------,
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* |- jump after finally |
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* `- catch any (local_n) v
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* jsr finally ---------------->|
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* throw local_n; |
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* finally: <-----------------------'
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* astore_n
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* ...
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* return_n
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*
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*
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* flow-block
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* finally-block
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* ---> try-header
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* finally {
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* ---> first-finally-instruction
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*
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* A synchronized block uses a similar technique:
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*
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* local_x = monitor object;
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* monitorenter local_x
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* try-header any
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* |- syncronized block
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* | ...
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* | every jump to outside is preceded by jsr monexit ---,
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* | ... |
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* |- monitorexit local_x |
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* | jump after this block (without jsr monexit) |
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* `- catch any (local_n) |
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* monitorexit local_x |
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* throw local_n |
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* monexit: <-----------------------------------------------'
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* astore_n
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* monitorexit local_x
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* return_n
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*/
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public boolean doT1 {
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/* search successor with smallest addr. */
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Enumeration enum = successors.elements();
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FlowBlock succ = null;
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while (enum.hasMoreElements()) {
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Jump jump = (Jump) enum.nextElement();
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if (jump == null)
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continue;
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FlowBlock fb = jump.destination;
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if (succ == null || fb.addr < succ.addr) {
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succ = fb;
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}
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}
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if (succ == null) {
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/* There are no successors at all */
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return false;
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}
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/* check if this successor has only this block as predecessor. */
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/* if not, return false. */
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if (succ.predecessors.size() != 1)
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return false;
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/* First find the innermost block that contains all jumps to this
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* successor and the last modified block.
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*/
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Enumeration enum = successors.elements();
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StructuredBlock appendBlock = lastModified;
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while(enum.hasMoreElements()) {
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Jump jump = (Jump) enum.nextElement();
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if (jump == null || jump.destination != successors)
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continue;
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while (!appendBlock.contains(jump.parent))
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appendBlock = appendBlock.outer;
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/* appendBlock can't be null now, because the
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* outermost block contains every structured block.
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*/
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}
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/* Update the in/out-Vectors now */
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updateInOut(successor, true);
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/* The switch "fall through" case: if the appendBlock is a
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* switch, and the successor is the address of a case, and all
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* other successors are inside the block preceding that case.
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*/
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if (case != null) {
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SwitchBlock switchBlock = (StructuredBlock) appendBlock;
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/* Now put the succ.block into the next case.
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*/
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switchBlock.replaceSubBlock(nextcase,succ.block);
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succ.block.outer = switchBlock;
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/* nextcase is not referenced any more */
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/* Do the following modifications on the struct block. */
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appendBlock = precedingcase;
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} else {
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/* Prepare the unification of the blocks: Make sure that
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* appendBlock has a successor outside of this block. This is
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* always possible, because it contains lastModified.
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*/
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if (appendBlock.jump == null) {
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/* assert(appendBlock.jump.getNextFlowBlock() != null) */
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appendBlock.setJump(appendBlock.getNextFlowBlock());
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}
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/* Now unify the blocks: Create a new SequentialBlock
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* containing appendBlock and successor.block. Then replace
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* appendBlock with the new sequential block.
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*/
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StructuredBlock outer = appendBlock.outer;
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StructuredBlock sequBlock =
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new SequentialBlock(appendBlock, switchBlock);
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outer.replaceSubBlock(appendBlock, sequBlock);
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sequBlock.outer = outer;
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}
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/* Try to eliminate as many jumps as possible.
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*/
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optimizeJumps(succ, appendBlock);
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/* Now remove the jump of the appendBlock if it points to successor.
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*/
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if (appendBlock.jump == succ)
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appendBlock.removeJump();
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/* If there are further jumps, put a do/while(0) block around
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* appendBlock and replace every remaining jump with a break
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* to the do/while block.
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*/
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/* Believe it or not: Now the rule, that the first part of a
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* SequentialBlock shouldn't be another SequentialBlock is
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* fulfilled. <p>
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*
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* This isn't easy to prove, it has a lot to do with the
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* transformation in optimizeJump and the fact that
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* appendBlock was the innermost Block containing all jumps
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* and lastModified.
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*/
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/* Set last modified to correct value. */
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lastModified = succ.lastModified;
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}
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public boolean doT2() {
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/* If there are no jumps to the beginning of this flow block
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* or if this block has other predecessors which weren't
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* considered yet, return false. The second condition make
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* sure that the while isn't created up to the first continue.
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*/
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/* Update the in/out-Vectors now */
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updateInOut(successor, false);
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/* If there is only one jump to the beginning and it is the
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* last jump and (there is a do/while(0) block surrounding
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* everything but the last instruction, or the last
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* instruction is a increase/decrease statement), replace the
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* do/while(0) with a for(;;last_instr) resp. create a new one
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* and replace breaks to do/while with continue to for.
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*/
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{
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/* Otherwise: */
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/* create a new while(true) block.
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*/
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/* Try to eliminate as many jumps as possible.
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*/
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optimizeJumps(this, block);
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/* Now remove the jump of block if it points to this.
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*/
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/* if there are further jumps to this, replace every jump with a
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* continue to while block and return true.
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*/
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}
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}
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public void removeSuccessor(Jump jump) {
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successors.setElementAt(null, successors.indexOf(jump));
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}
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}
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